1A. Subjective effects

Although psychedelics vary in regards to their chemical families, they exhibit a distinctive and to a great extent homogenous set of typically co-occurring subjective effects (i.e. alterations in the user's conscious experience) (Milliere, 2017: 5). At equivalent moderate dosages, the subjective differences between various psychedelic compounds are largely a matter of intensity and ‘flavour’ of the experience (with one notable exception: some psychedelics do not significantly alter visual perception, which will be addressed in Part 2) (Wallach, 2009: 93). The phenomenologically distinctive feature of psychedelics is, in essence, their tendency to produce altered states of consciousness significantly influenced by the user's ‘set and setting’ (i.e. state of mind and immediate physical and interpersonal environment) and characterised by wide-ranging, non-negligible changes in sensory, affective, self-perceptive, temporal, and spatial phenomenal modalities (Letheby, 2015: 173).

A complete description of the entire spectrum of psychedelic phenomenology lies outside the spatial constraints of this paper — for the present purposes, it will suffice to simply group psychedelic experiences into three broad levels of cumulative subjective intensity, roughly correlative with dosage and specific compound ingested. Level 1 is occasioned by virtually all psychedelics at low to moderate dosages and is characterised by geometric visual hallucinations (i.e. a perceived overlay of geometrically patterned imagery on top of visible surfaces at lower dosages and geometric metamorphosis of objects at higher dosages), synesthesia (i.e. experience of one sensory stimulus through two or more sensory modalities simultaneously), and emotional intensification — thus exhibiting significant effects only in regards to sensory perception and affective experience (Dell’erba, Brown, & Proulx, 2018: 127; Frecska, 2018: 163; Letheby, 2015: 174). At Level 2, self-consciousness and temporal perception become significantly affected. Level 2 is occasioned by virtually all psychedelics at moderate to high dosages and, in addition to Level 1 effects, characterised by ego dissolution (i.e. where the subjective boundary between the self and the external world is deactivated and replaced with a sense of metaphysical continuity with the immediate environment as well as the world at large, thus ‘dissolving’ one's ego, or sense of self, and by implication, the sense of corporeal embodiment) and time dilation (i.e. perceived deceleration in, or even complete stoppage of the passage of time) (Letheby & Gerrans, 2017: 6).

Level 3 is occasioned most reliably (and perhaps exclusively) by high dosages of N,N-DMT and denotes the anecdotally termed ‘breakthrough’ experience: in essence, a psychedelic experience which, in addition to a hyperintensified set of Level 2 effects, exhibits extreme alterations in spatiotemporal (i.e. both temporal and spatial) perception, subjectively perceived as a transportation through a spatiotemporally boundless multiverse to seemingly autonomous, altogether “alien” realities (Emilsson, 2016b; Gallimore, 2013: 456–458; Psychedelic Community, 2020). For reasons of empirical consistency, I will take ‘breakthrough psychedelic experiences’ to be equivalent to ‘higher-dosage subjective effects of N,N-DMT (hereafter simply ‘DMT’)’, although it remains to be empirically verified whether ‘breakthrough’ subjective effects are occasioned exclusively by high dosages of DMT or whether they simply constitute the highest level of progressive complexity of all psychedelic phenomenology.

Although the potent psychoactive effects of DMT, a naturally occurring compound found in numerous plant and animal species, are not a new discovery for humanity at large — in fact, DMT is the main component in ayahuasca, an orally-administered traditional brew that has been used by indigenous Amazonian populations as a multi-purpose medicinal agent at least for centuries, if not for millennia — DMT was first lab-synthesized only in 1931 and identified as psychoactive in 1956 (Blakemore, 2019; Barker, 2018: 2; Frecska et al. 2016: 1; Gallimore, 2013: 455–456; Letheby, 2017: 174; Manske, 1931: 592; Szara, 1989: 237). As opposed to the oral route of administration in the form of ayahuasca — whose onset is slow and gradual and whose total duration of action spans across multiple hours — the ingestion of the pure (i.e. chemically isolated) form of DMT through vaporisation or injection results in a significantly shorter experience: the onset takes place within a matter of mere seconds, peak subjective intensity is reached within two minutes, and the average total duration of action including residual after-effects is only fifteen to sixty minutes (Barker, 2018: 5, 10; Gallimore, 2013: 456; Psychedelic Community, 2020). Accordingly, because of the exceptionally brief timescale between onset and peak effects unique to vaporised and injected DMT, the monumental subjective intensity of ‘breakthrough’ effects is most frequently and reliably achieved through vaporisation and injection, as opposed to the oral route of DMT administration (Gallimore, 2013: 456, 486–487).

In turn, it follows to elaborate on the phenomenology exclusive to psychedelic experiences at the ‘breakthrough’ level. The perceptual content of ‘breakthrough’ experiences is multi-sensory and primarily visual, characterised by fully immersive hallucinations of ‘crystal’ worlds constituted entirely out of energy or information through which the user moves at the outset, often followed by interactive, telepathic encounters with entities that are alien-like, elf-like, insect-like, or human-archetypal (such as spirits or deities) in the form of eidetic hallucinations (i.e. where the hallucinated content emerges from a pre-existing interference pattern) that are typically surrounded by visions of hyperadvanced technology, environments, semantic networks, and linguistic systems (Emilsson, 2016b; Gallimore, 2013: 475–476; Kent, 2010: 90–91; Kins, 2019; Strassman, 2001: 179). In terms of structure, ‘breakthrough’ experiences typically exhibit geometry that is hyperbolic (i.e. a surface with constant negative curvature) and fractal (i.e. scale-free, geometrically constant arrangement) — in regards to both objects and the surrounding space itself, and the surrounding space in turn exhibits extra-dimensional spatiotemporal complexity (i.e. comprised of more than three physical dimensions of space and one dimension of time, beyond those of ordinary physical reality) (Emilsson, 2016b; Psychedelic Community, 2020; Strassman, 2001: 181).

Furthermore, the semantic content of ‘breakthrough’ experiences typically comprises representations of knowledge that seemingly extends beyond the scope of human comprehensibility, as well as of mind-independence about the experience's metaphysical aspects (i.e. the nature and structure of objects, entities, and worlds encountered during the experience) — accompanied by overarching epistemic feelings of lucidity (i.e. lack of impairment of mental functioning) and veridicality (i.e. objective truthfulness) (Frecska, 2018: 172; Gallimore, 2013: 475–476; Kins, 2019; Psychedelic Community, 2020). Lastly, the aforementioned phenomenal characteristics of ‘breakthrough’ experiences are indeed typical — they are “strikingly” common across users (Gallimore, 2013: 482–483). In turn, this gives rise to the ‘hard problem’ of psychedelic phenomenology (‘HPPP’) — specifically, in regards to its ‘breakthrough’ level.

1B. The ‘hard problem’ of psychedelic phenomenology

In essence, the HPPP can be stated as follows: why exactly do ‘breakthrough’ psychedelic experiences have the common phenomenology that they have?

In order to conclusively resolve the HPPP, however, a conclusive resolution to the Hard Problem of Consciousness (i.e. explaining the exact relationship between neurocognitive processes and conscious experience) is required, which is yet to be found — the shared element between these two problems being an inquiry into the nature of conscious experience (Chalmers, 1997; Maldonato & Dell’Orco, 2010: 213). Nevertheless, it is possible to at least narrow down the range of plausible explanations on which a conclusive resolution to the HPPP could be based: because of the phenomenological cross-commonality that ‘breakthrough’ experiences exhibit, they must be directly ontologically dependent on some objective fundamental factors, which gives rise to the metaphysical internalism-externalism debate central to this paper — whether these factors are internal (i.e. exist within individual human brains) or external (i.e. exist outside of individual human brains). In turn, the answer to this question will depend on explanations about the phenomenal characteristics and the apparent phenomenal objectivity exhibited by ‘breakthrough’ experiences. Accordingly, the HPPP can be broken down into three interdependent questions:

1. A)The Ontological Dependence Question (‘ODQ’): are the factors which ‘breakthrough’ phenomenology is directly ontologically dependent on internal or external?
2. B)The Phenomenal Characteristics Question (‘PCQ’): how can the ‘alien’ perceptual content, the extraordinarily complex structure, and the ‘transhuman’ semantic content of ‘breakthrough’ experiences be explained?
3. C)The Phenomenal Objectivity Question (‘POQ’): how can the phenomenological cross-commonality and perceived veridicality of ‘breakthrough’ experiences be explained?

Thus, in order to even begin approaching the HPPP, its subcomponents (the ODQ, the PCQ, and the POQ) must first be addressed, the implications of which may also help us progress further towards a resolution to the Hard Problem of Consciousness, not least because ‘breakthrough’ experiences seem to stretch consciousness to its very limits.

2A. Neural representation

From a strictly neurological perspective, for any world to be perceptible, at least some part of the informational structure of that world must be neurally represented — thus, the external world is never directly perceptible, but only so indirectly, through its neural representation (Gallimore, 2013: 458–459, 470). Accordingly, on the general internalist view, ‘breakthrough’ worlds must have a neural representation that is accessed during ‘breakthrough’ experiences and the construction of this representation is explainable via the neural processes that construct, develop, and stabilise the representation of our consensus world: the external world that individual conscious agents can commonly agree to be the world which they inhabit in the state of ordinary waking consciousness (Gallimore, 2013: 459, 470). Neural world-representation processes will be outlined first, which will provide a basis for the subsequent development and analysis of the strong internalist (Section 2B) and weak internalist (Section 2C) positions on psychedelic phenomenology (Gallimore, 2013: 459, 470).

The neuroscientific consensus is that neural representations are constructed from external-world information which is encoded by patterns of neuronal connectivity in the cerebral cortex (Gallimore, 2013: 459). Comprised of columns of six neuronal layers, the cerebral cortex is partitioned into functionally segregated regions that correspond to, inter alia, the various sensory modalities (i.e. the visual, auditory, gustatory, olfactory, somatosensory, somatomotor, and metacognitive cortices), which are further partitioned into billions of functionally segregated subregions in the form of neuronal columns that correspond to their modal subcomponents (e.g. motion, colour, shape, texture, orientation, etc. in the visual cortex), which allows for a huge range of nonconceptual (i.e. perceptually irreducible) content to be representable (Gallimore, 2013: 459–462). In turn, functional segregation and multi-layered neuronal structure allow cortical subregions to be simultaneously activated in an almost limitless number of highly specific, three-dimensional neuronal ‘activation patterns’ — resulting in functional integration, which enables their respective nonconceptual content representations to be integrable into an almost limitless number of conceptual content representations (i.e. additive constructs of nonconceptual content, e.g. ‘forward movement of an orange sphere’), as a result of which the external world appears highly cohesive, complex, and phenomenally varied (Gallimore, 2013: 460–463).

Although the Binding Problem (i.e. causally explaining the transition from functional segregation to functional integration) remains an open empirical question, the neuroscientific consensus is that perceptual binding is a product of cortical interconnectivity (i.e. physical connections between functionally segregated neuronal columns across the entire cortex which allow for strong and rapid interactions) (Edelman, 2000; Gallimore, 2013: 462–464). Cortical interconnectivity is made possible by the thalamus, a neural structure through which all sensory information except the olfactory passes before it is received by the cortex (Sherman & Guillery, 2002: 1695). Each functionally segregated neuronal column in the cortex is reciprocally connected to a thalamic region, forming functionally specific thalamocortical loops — which, when activated, produce oscillatory electrical signals (Gallimore, 2013: 464–465). In addition to functionally specific thalamocortical loop connections, thalamic regions also project neurons to other, non-functionally corresponding cortical subregions — constituting non-functionally specific thalamocortical connections, which thus enable connectivity between sets of thalamocortical loops, resulting in their functional integration (Gallimore, 2013: 464–465). It has been observed that thalamocortical loop oscillations in the gamma range (20–60 Hz) correlate with the synchronous activation of functionally segregated neuronal columns (Engel & Singer, 2001: 16; Wang, 2010: 1195). Moreover, when a particular set of thalamocortical loops is synchronously activated, their gamma oscillations synchronise in mere milliseconds, forming a transiently unified, unique neuronal structure — a thalamocortical state (Gallimore, 2013: 464). In turn, as a product of functional segregation and integration modulated by the thalamocortical system, each unique thalamocortical state yields a representation of a unique, cohesive conscious state — a moment of conscious experience — and this is in principle applicable to all conscious states, ordinary or altered (Gallimore, 2013: 465).

In order to explain how the thalamocortical system constructs, develops, and stabilises the representation of the consensus world, cortical interconnectivity must be examined in more detail, of which there are two types: structural and functional — the former denotes semi-permanent, physical connections that are static and stable within the seconds-minutes timeframe, gradually strengthened or weakened in the hours-days timeframe depending on the frequency of their activation, and the latter denotes highly dynamic, transient correlations of synchronous activation, which change in the timeframe of milliseconds depending on external information (i.e. sensory information input from the external world) and current internal thalamocortical activity (i.e. thalamocortical state information continuously generated within the brain through functional segregation and integration) (Gallimore, 2013: 465–467). A reciprocal causal relation thus exists between them: structural connectivity patterns determine the range of functional connectivity patterns more likely to be activated, and conversely, functional connectivity patterns gradually strengthen or weaken structural connectivity patterns such that current internal thalamocortical activity continues to match the patterns of external information continuously received through evolution, ontogenic development, and conscious experience as closely as possible (Gallimore, 2013: 467–468). Eventually, very little external input is needed in order to construct world representations, evidenced by the brain's ability to construct dream worlds without receiving any external information in real-time — entirely through internal thalamocortical activity analogous to that which takes place during waking, using the same, previously developed repertoire of thalamocortical states and also exhibiting gamma oscillation synchronisation (Edelman, 2000; Gallimore, 2013: 468; Massimini et al. 2010: 176).

Accordingly, the considerations above contextualise the subsequently divergent debate on psychedelic phenomenology, which can be outlined as follows: whether the neural representation of ‘breakthrough’ worlds is modulated entirely by internal brain activity (strong internalism, Section 2B), analogously to dream worlds, or whether it is also modulated by external information, analogously to the consensus world — and if the latter, whether this information is accessed entirely via an alternative evolutionary world-representation already contained in the brain (weak internalism, Section 2C) or at least partially received in real-time from an otherwise unperceived, fully autonomous alternate dimension or reality (externalism, Part 3) (Gallimore, 2013: 470, 492). The interpretative implication here is that strong internalism regards ‘breakthrough’ phenomenology as an elaborate hallucination, whilst weak internalism and externalism both subscribe to the ‘channel-tuning’ thesis — the idea that during breakthrough experiences, consciousness ‘tunes’ to a different ‘world channel’ — and diverge on whether the locus of the ‘psychedelic channel’ is internal or external, respectively (Letheby, 2017: 631–632; Strassman, 2001: 311).

2B. Strong internalism

The strong internalist position on psychedelic phenomenology subscribes to the ‘elaborate hallucination’ thesis, which can be stated as follows: psychedelics produce their phenomenology entirely through the destabilisation of internal brain activity and are therefore agents of perceptual misrepresentation, which means that the epistemic feelings of lucidity and veridicality occasioned by ‘breakthrough’ experiences are in fact illusory (Kent, 2010: 71; Letheby, 2017: 631–632).

The ‘elaborate hallucination’ thesis is fundamentally premised on psychedelic neuropharmacology and its relation to neural representation. In respect to the neuropharmacological mechanisms of action of psychedelics, the principally affected neurotransmitter (i.e. a compound which regulates brain activity) is serotonin (5-HT): a neuromodulator (i.e. a category of neurotransmitter which alters the excitatory and inhibitory action of neurons on a global scale, which means that such a compound influences the activity of the entire cerebral cortex) whose neurobiological functions not only comprise the regulation of mood, sleep, memory, appetite, and involuntary action of muscles that control blood pressure and digestion — but also the modulation of internal thalamocortical activity (Gallimore, 2013: 468, 470; Kent, 2010: 59). Out of the seven recognised types of serotonin receptors (5-HT1 to 5-HT7), the 5-HT2A receptor subtype is central in producing the subjective effects of psychedelics: it has been observed that the subjective intensity of any particular psychedelic strongly correlates with the intensity of its 5-HT2A receptor affinity and, furthermore, 5-HT2A has been traditionally linked to the visual subjective effects of psychedelics (Kent, 2010: 62; Kraehenmann et al. 2017: 2031; Nichols, 2004: 131).

The activation of 5-HT2A receptors, which are abundant in cortical pyramidal neurons (i.e. the excitatory neurons that form the cortical component of a thalamocortical loop), increases the probability that their respective pyramidal neurons will be activated — in contrast, the activation of 5-HT1A receptors, located alongside 5-HT2A receptors, decreases this probability, as a result of which these two receptor subtypes have an opposing relation in respect to neuronal excitability (Araneda & Andrade, 1991: 399). Accordingly, the balance between 5-HT2A and 5-HT1A receptor activation in cortical pyramidal neurons determines the level of neuronal excitability across the entire cerebral cortex (Gallimore, 2013: 471). Exhibiting the same opposing relation, 5-HT2A and 5-HT2A receptors are also present in inhibitory interneurons, which are regarded as central in generating thalamocortical gamma oscillations (that correlate with neuronal column synchronisation, resulting in specific thalamocortical states, as mentioned previously) and, in addition, a subpopulation of interneurons in the fourth layer of the cortex is responsible for the global synchronisation of gamma oscillations (Cardin et al. 2009: 663; Llinas, Ribary, Contreras, & Pedroarena, 1998: 1841). In effect, the balance between 5-HT2A and 5-HT1A receptor activation in cortical pyramidal neurons and inhibitory interneurons — which modulates neuronal excitability and the generation and synchronisation of gamma oscillations, respectively — is central in the modulation of internal thalamocortical activity, and thus, the manner in which the brain represents the external world (Gallimore, 2013: 471).

In states of ordinary waking consciousness, 5-HT2A and 5-HT1A receptor subtypes are activated and occupied by serotonin, which regulates the balance between their activation (Nichols, 2004: 148). However, since psychedelics are partial agonists (i.e. activators) of the 5-HT2A subtype (to which they bind in competition with serotonin) and do not significantly affect the 5-HT1A subtype, the 5-HT2A-5-HT1A activation balance is destabilised in psychedelic states — in favour of significantly elevated neuronal excitability and thus hypersensitivity to incoming external information, as well as significantly elevated generation and global synchronisation of gamma oscillations and thus the expression of novel, hyperintegrated thalamocortical states (Gallimore, 2013: 472–473). Subjectively, the combination of hypersensitivity to external information and novel, hyperintegrated thalamocortical states is likely to result in multimodal perception as well as novel conceptual interpretations of incoming external information, which thus provides a strong internalist explanation of Level 1 effects — synesthesia and geometric visual hallucinations, respectively, and emotional intensification being explainable as a natural response to unforeseen novelty (Gallimore, 2013: 473). Moreover, fully immersive hallucinations of ‘alien’ worlds, hyperadvanced environments, technology, semantic networks, linguistic systems, as well as entity-emergent eidetic hallucinations that characterise the perceptual content of ‘breakthrough’ experiences can also be explained this way — as the subjective products of a novel repertoire of hyperintegrated thalamocortical states — according to strong internalism: ‘alien’ corresponding to ‘novel’ and ‘hyperadvanced’ corresponding to ‘hyperintegrated’ (Gallimore, 2013: 473).

However, it has been objected that the Integrated Information Theory-based ‘hyperintegration’ model outlined above is inconsistent with early empirical observations of an overall decrease in internal thalamocortical activity in respect to both psilocybin and ayahuasca experiences (Carhart-Harris et al. 2012: 2138; Frecska et al. 2016: 7; Riba et al. 2002: 613). Nevertheless, this objection is refutable on both theoretical and empirical grounds. First, according to IIT (the theoretical basis of the ‘hyperintegration’ model), at any given time, inactive neurons contribute to the expression of a thalamocortical state equally to those that are activated — the relevant factor here is the overall conceptual structure specified by an activation pattern, not activation itself — and thus, the assumption that neurons contribute to integration only if they are activated is misguided (Tononi & Koch, 2015: 9–10). Moreover, a more recent neuroimaging study revealed that, following LSD ingestion, integration is indeed significantly elevated in the visual cortex — strongly correlating with visual subjective effects, which is consistent with the primarily visual nature of LSD experiences — and decreased in the numerous cortical regions of the Default Mode Network (DMN), strongly correlating with ego dissolution effects, which thus explains why an overall (but not complete) decrease in internal thalamocortical activity may be observed during psychedelic experiences, given their tendency to exhibit strong ego dissolution effects at moderate to high dosages (Carhart-Harris et al. 2016: 4853, 4856).

Functionally, the DMN does not significantly influence sensory perception, which means that its disintegration is not inconsistent with the prediction of hyperintegration of sensory perception-specific cortical regions during psychedelic experiences (Carhart-Harris et al., 2014: 6). Instead, the DMN modulates, inter alia, metacognition (e.g. self-reflection and introspection), temporal perception (i.e. simulation of past and future events), and minimises prediction errors about one's spatial location and bodily awareness, which — taken together with its observed disintegration correlative with ego dissolution effects — has promoted the consensus view in neuroscience that the DMN is the direct neural correlate of self-consciousness (Carhart-Harris et al., 2014: 6; Letheby, 2017: 634–635; Letheby & Gerrans, 2017: 7–8; Milliere, 2017: 15). Accordingly, the disintegration of the DMN during psychedelic experiences provides a strong internalist explanation for Level 2 effects — ego dissolution and time dilation — as well as the feelings of ‘alienness’ in respect to the user's perceived location that characterise psychedelic experiences at the ‘breakthrough’ level. Furthermore, DMN disintegration gives rise to the metaphysical implication that self-consciousness is not necessary for conscious experience, which is consistent with the Buddhist phenomenalist view that self-consciousness is an emergent, not a fundamental phenomenon (Coseru, 2018: 97–98; Letheby, 2015: 187). Interestingly, although incidentally, meditation — one of the practical aspects of Buddhist phenomenalism — also results in DMN disintegration when practiced long-term, albeit to a lesser extent than acute psychedelic experiences (Fingelkurts, Fingelkurts, & Kallio-Tamminen, 2016: 27).

The aspects of ‘breakthrough’ experiences that remain to be explained from the strong internalist position are their structure and semantic content, which can be done from the premise that the transition of the thalamocortical system from a stabilised, integrated state to a destabilised, hyperintegrated state that occurs with the onset of a psychedelic experience can be described in mathematical terms — as a transition from dynamical linearity to nonlinearity (Kent, 2010: 71). Nonlinear dynamical systems generate exponential complexity of (in this case, perceptual) output in proportion to (in this case, informational) input, where the output feeds back on itself until its complexity reaches infinity and where small changes in input result in unpredictable, highly divergent sets of output values — in contrast, linear dynamical systems generate sequential output complexity, where small changes in input result in stable, predictable output values (Kent, 2010: 75–77). In states of ordinary waking consciousness, 5-HT2A receptors in the pyramidal neurons of the fifth cortical layer project oscillatory electrical signals (which are produced by thalamocortical loops, as discussed previously) upward into the first cortical layer in the form of linear feedback loops, binding perceptual information across the entire cortex in order to produce a predictable representation the external world — accordingly, in psychedelic states, where the 5-HT2A-5-HT1A activation balance is destabilised, these feedback loops become nonlinear, according to strong internalism (Kent, 2010: 68–71, 76).

Thus, subjectively, the nonlinearity of cortical feedback loops presumably occasioned by psychedelics would result in perceptual output progressively feeding back on itself, generating infinitely increasing exponential complexity to the point of total perceptual overload, which thus provides a general explanation for the ‘monumental’ subjective intensity that characterises ‘breakthrough’ experiences (Kent, 2010: 78–79). Furthermore, since nonlinearity describes the destabilisation of the 5-HT2A-5-HT1A activation balance that affects the entire thalamocortical system, nonlinearity applies to any informational input and thus can be used to explain any specific aspect of ‘breakthrough’ experiences that follows its general principle of infinitely increasing complexity. Accordingly, nonlinearity can be used to explain the ‘extraordinarily complex’ structure of ‘breakthrough’ experiences: in respect to spatial informational input, nonlinear feedback loops would subjectively result in infinitely increasing geometric complexity — first, in respect to objects and as time progresses, the surrounding space itself — extending beyond the three dimensions of space perceived in states of ordinary, linear consciousness; in respect to temporal informational input, infinitely increasing temporal complexity would obtain such that, in combination with the nonlinear amplification of spatial informational input, it would be possible to perceive the same spatiotemporal input as an extra-dimensional, spatiotemporally infinite multiverse (Kent, 2010: 78–79). Moreover, according to the ‘nonlinearity’ model, the fractal and hyperbolic properties that characterise the geometry of ‘breakthrough’ experiences are nothing more than a subjective rendering of nonlinear feedback loops, since these properties are consistent with the basic principle of nonlinearity and are indeed traditionally regarded as mathematically nonlinear (Emilsson, 2016b). In effect, according to the ‘nonlinearity’ model, the ‘extraordinarily complex’ structure of ‘breakthrough’ experiences is simply another aspect of the ‘extraordinarily elaborate’ hallucination typically occasioned by high dosages of DMT.

Furthermore, the ‘nonlinearity’ model can be empirically substantiated: it has indeed been demonstrated that nonlinear dynamical activity occurs in the human brain — entailed by the observation that electrical signal activity in the human cortex measured by an electroencephalograph can be graphically represented in abstract space in the form of higher-dimensional (i.e. above three abstract dimensions) fractal attractors using the technique of delay coordinate embedding (i.e. plotting data against itself across a constant time interval in higher mathematical dimensions), up to the value of 4.8 dimensions (Walling & Hicks, 2003: 164–165). The term ‘fractal’ denotes mathematically irregular shapes that lie between discrete dimensions, whose structure is nonlinear and scale-free — it remains self-similar irrespective of the scale of magnification — as a result of which the lines of a fractal shape are infinitely long yet remain confined to finite space, whilst ‘attractor’ denotes the pattern created through the graphic representation of sets of output values determined by continuously changing input values (Walling & Hicks, 2003: 161–162). Higher-dimensional fractal attractors have also been observed in the electrical signal activity of the brains of other species, where the highest graphically representable dimension that generates a fractal (as opposed to random scattering) in relation to a particular species correlates with the presumed stage of evolutionary development of that species (Walling & Hicks, 2003: 165). Based on these observations and the principle that the higher the dimension of a fractal attractor, the more variables are required to represent it, it is plausible that the higher the mathematical complexity with which electrical signal activity in the cortex of a particular species can be graphically represented such that a geometrically meaningful result obtains (in this case, a fractal) — revealing an underlying mathematical order — the more overall integration the cortex of that species would exhibit in its representation of the external world (Walling & Hicks, 2003: 165–166).

Moreover, the suggestion above is consistent with the view in evolutionary psychology that the capacity for abstract thinking, as well as the integration of, inter alia, conceptual and emotive information evident in human consciousness are evolutionary developments and thus are not unchanging, objective aspects of perception (Adamski & Borowik, 2014: 88; Zaborowski, 1998: 48). Accordingly, it has been argued that in order for a conscious perceptual system to have a psychedelic experience that contains seemingly objective semantic content, that system must possess the capacity for abstract thinking, as well as exhibit the integration of conceptual and emotive content (Kent, 2010: 15–16). As a result, on the strong internalist view, the semantic content as well as the accompanying epistemic feelings of lucidity and veridicality that characterise ‘breakthrough’ experiences are illusions made possible through the evolutionary development of human metacognition — a product of an evolutionary increase in the functional integration of the human cortex — and thus, the cross-commonality of ‘breakthrough’ psychedelic phenomenology is simply a result of these universally shared properties of the human brain. Therefore, according to strong internalism, psychedelic phenomenology is — at all of its levels — an elaborate hallucination produced entirely through internal brain activity and thus, essentially, an illusion.

However, as compelling as the strong internalist position appears at this stage, more recent neuropharmacological research and philosophical arguments have given rise to the weak internalist position on psychedelic phenomenology, which attempts to further increase the explanatory power of the general internalist view that psychedelic phenomenology is fundamentally explainable through neurological facts, but rejects the strong internalist ‘elaborate hallucination’ thesis.

2C. Weak internalism

In this section, it will be shown that the weak internalist position renders the ‘elaborate hallucination’ thesis somewhat theoretically primitive and empirically outdated — though it must be noted that weak internalism, in comparison with strong internalism, nevertheless involves a greater degree of speculation, whose plausibility will become more accurately ascertainable only with the future progression of empirical research on psychedelics.

Although there is strong neuropharmacological evidence that psychedelics are agonists of the 5-HT2A serotonin receptor subtype (as has been discussed in the previous section), the full extent of the mechanism of action of psychedelics remains an open empirical question — indeed, more recent proposals have suggested that the primary neuroanatomical site of psychedelic action could be another class of receptors altogether: the trace amine-associated receptors (‘TAARs’), of which there are six subtypes in the human brain and which are present throughout the central nervous system including areas linked to sensory perception (Gainetdinov, Hoener, & Berry, 2018: 549; Gallimore, 2013: 474; Wallach, 2009: 91–92). Whilst the neurobiological function of TAARs in humans has not been empirically settled with conclusive effect, it has been shown that TAARs indeed modulate sensory perception in insects and that a specific mutation in the TAAR6 receptor strongly correlates with the hallucinatory symptoms of schizophrenia, which suggests that the TAAR6 is likely to at least partially modulate sensory perception in humans (Scheiner, Oney, Blenau, & Erber, 2002: 545; Vladimirov et al. 2007; Wallach, 2009: 91). Moreover, it has been observed that several TAAR subtypes allow the binding of neurochemicals other than the classical trace amines (p-tyramine, beta-phenethylamine, tryptamine, and octopamine), which suggests the existence of additional endogenous (i.e. naturally occurring within the body) TAAR ligands (i.e. endogenous neurochemicals which bind to a particular receptor) (Zucchi, Chiellini, Scanlan, & Grandy, 2006: 967). ‘Trace’ denotes the exceptionally low concentrations at which these neurochemicals occur in the brain, whilst ‘amine’ denotes a class of neurochemicals that contain a nitrogen atom hanging off a carbon ring, which includes, inter alia, serotonin, dopamine, and noradrenaline — neuromodulators — whose function is to control the global timing of neuronal activation in the entire cortex (Gallimore, 2013: 470, 474; Kent, 2010: 57). Furthermore, naturally occurring psychedelics DMT, 5-MeO-DMT, and psilocybin are highly similar in chemical structure to the neuromodulator serotonin and the trace amine tryptamine, and are also classified as amines (Kent, 2010: 57–58). Moreover, it has been shown that DMT and 5-MeO-DMT naturally occur at trace concentrations in the human brain, blood, cerebral spinal fluid, and urine, which has given rise to the neuroscientific consensus that these psychedelics are endogenous metabolites and thus have a natural neurobiological function in humans — as opposed to being solely exogenous chemicals without any natural neurobiological function whose strong psychoactive effects are explainable via their chemical structure and particular receptor affinity alone (e.g. LSD or methamphetamine) (Dean et al. 2019; Wallach, 2009: 91). Yet, although it has been over 55 years since the discovery of the endogenous psychedelics, their exact natural neurobiological function still remains a matter of debate (Corbett, Christian, Morin, Benington, & Symthies, 1978: 139; Franzen & Gross, 1965: 1052; Frecska et al. 2016: 2; Gallimore, 2013: 483). Thus, in accordance with the considerations above and the fact that the endogenous ligand of the TAAR6 receptor remains unknown, it has been argued that the endogenous ligand of the TAAR6 receptor may be one or more of the endogenous psychedelics and — because of the similarities in chemical structure and phenomenology at low to moderate dosages that psychedelics exhibit as a class — that TAAR6 may constitute another significant site of action in respect to all psychedelics, alongside the 5-HT2A receptor (Wallach, 2009: 91).

The view that the 5-HT2A receptor is not the only significant site of psychedelic action has been substantiated on the basis that 5-HT2A agonism alone is unable to account simultaneously for both the lack of visual subjective effects in, inter alia, 5-MeO-DMT experiences, and the presence of visual subjective effective in, inter alia, DMT, LSD, and psilocybin experiences — even though it has been shown that the non-visual 5-MeO-DMT exhibits higher 5-HT2A receptor affinity than the highly visual DMT — thus, if the 5-HT2A receptor were the only significant site of psychedelic action, this difference would not exist (McKenna, Repke, Lo, & Peroutka, 1990: 196; Wallach, 2009: 91, 93). However, it has been objected that the lack of visual effects pertinent to 5-MeO-DMT is due to the fact that 5-MeO-DMT also has a higher affinity for the 5-HT1A receptor than DMT, based on the observation that the co-administration of DMT and a 5-HT1A antagonist increases the subjective intensity of the highly visual DMT experience, which suggests that 5-HT1A agonism may inhibit visual effects — and thus, the 5-HT2A receptor remains the sole significant site of psychedelic action (Strassman, 1996: 121; Wallach, 2009: 93). Nevertheless, this is successfully refutable via a counterexample — AMT: a psychedelic which exhibits high 5-HT2A affinity and significantly lower 5-HT1A affinity, yet produces only minimal visual effects — accordingly, because 5-MeO-DMT and AMT exhibit different levels of 5-HT1A affinity yet both lack significant visual effects, it is implausible that 5-HT1A agonism indeed inhibits visual effects, which means that the subjective effects of psychedelics cannot be explained via 5-HT2A agonism alone (Wallach, 2009: 93; McKenna et al. 1990: 196). Moreover, the empirical study that led to the conclusion that the 5-HT2A receptor is the sole significant site of psychedelic action — where it has been observed that the entire spectrum of the subjective effects of psilocybin can be neutralised by 5-HT2A antagonists ketanserin and risperidone — took place in 1998, before the discovery of the TAAR class in 2001, and because it remains unknown whether ketanserin and risperidone also have an antagonistic effect on TAARs, it is certainly plausible that not only the 5-HT2A receptor, but also one or more of the TAARs (TAAR6 being the most likely candidate, as discussed above), constitutes a significant site of psychedelic action, which would explain why all classical psychedelics are 5-HT2A agonists yet not all of them produce visual effects (Vollenweider, Vollenweider-Scherpenhuyzen, Babler, Vogel, & Hell, 1998: 3897; Wallach, 2009: 92–93).

It has been further argued that if the TAAR class is indeed involved in the neuropharmacological mechanism of action of psychedelics, especially DMT, ‘breakthrough’ effects must be primarily — not only significantly — mediated by the TAAR class, not the 5-HT receptor class (Wallach, 2009: 92). It has been shown that the activation of the 5-HT1 and 5-HT3 receptor groups produces anxiolytic effects in mice and that DMT is an agonist of the 5-HT1 receptor group, which means that the anxiolytic effects occasioned by DMT only at threshold-level dosages (i.e. the lowest dosage range at which any subjective effects are noticeable) are more likely to be mediated by the 5-HT receptor class than the TAAR class (Delgado et al. 2005: 9; McKenna et al., 1990: 196; Strassman, 1996: 121). However, given that one or more of the endogenous psychedelics is likely to be an endogenous ligand the TAAR6 receptor (which is likely to at least partially modulate sensory perception in humans, as discussed above) and not any of the 5-HT receptors (whose endogenous ligand is widely accepted to be solely serotonin), the extreme alterations in sensory perception that characterise ‘breakthrough’ experiences occasioned by exogenously administered DMT at sufficiently high dosages are likely to be primarily mediated by the TAAR class, and only secondarily by the 5-HT class (Nichols, 2004: 148; Wallach, 2009: 92). In effect, it is certainly plausible that the TAAR class is only activated at dosages sufficient to produce ‘breakthrough’ effects and that effects at threshold-level to sub-‘breakthrough’ dosages are significantly mediated solely by the 5-HT class, in the manner proposed by the strong internalist ‘elaborate hallucination’ thesis based on the ‘hyperintegration’ and ‘nonlinearity’ models discussed in Section 2B (Wallach, 2009: 92). Thus, on the weak internalist view, the strong internalist position must apply only to sub-‘breakthrough’ phenomenology (where the TAAR class is presumably not activated) and that ‘breakthrough’ phenomenology (where the TAAR class is presumably activated) instead replicates the natural neurobiological function of endogenous DMT associated with the TAAR class — a function likely to be directly or indirectly related to the modulation of sensory perception, given the plausibility that DMT is an endogenous ligand of the TAAR6 receptor and that the TAAR6 receptor is at least partially involved in the modulation of sensory perception (Wallach, 2009: 92).

Moreover, the traditional view that the natural neurobiologicalfunction of DMT is anxiolytic – associated withits threshold-level dosage effects, presumably reflecting itslow endogenous concentrations in humans – can be ruledout, since, given the plausibility that DMT is an endogenousligand of the TAAR6 receptor and that its anxiolytic effectsare likely to be mediated by the 5-HT1 receptor groupinstead, the natural neurobiological function of DMT ismore likely to be linked to its presumably TAAR-mediated‘breakthrough’ sensory effects than to its 5-HT-mediatedanxiolytic effects (Jacob & Presti, 2005: 930; Wallach, 2009: 92).

Moreover, the traditional view that the natural neurobiological function of DMT is not associated with its high-dosage sensory effects (which on this view are merely incidental to its anxiolytic effects) is also implausible: in order to sustain the this view, the high-dosage sensory effects of DMT must be interpreted as unnatural, unnecessary, or unsafe within the typical dosage range that produce ‘breakthrough’ effects – and yet, the opposite is true: high-dosage ‘bbreakthrough’ sensory effects of DMT pose no risk of physical harm in a supervised setting, are typically accompanied by strong feelings of lucidity and veridicality (as opposed to cognitive impairment or intoxication) and have been used intentionally and extensively for medicinal, therapeutic, and spiritual purposes by indigenous Amazonian populations throughout history, as well as have recently regained popularity among Western researchers and psychotherapists, reflecting the shift towards a psychedelic renaissance (Gallimore, 2013: 484–485; Frecska et al. 2016: 1). Accordingly, if the natural neurobiological function of DMT could be associated with its high-dosage sensory effects and if these effects are mediated by the TAAR class (as discussed above), then it is likely that the natural neurobiological function of DMT is related, directly or indirectly, to the modulation of sensory perception (primary to any such function related to low-dosage anxiolytic effects).

This view has been further substantiated through the well-received and evidentially compelling — yet at this stage, still inconclusive — recent hypothesis that DMT is an endogenous neurotransmitter, whose physiological function may also extend to neuromodulation (Barker, 2018: 11–12). First, DMT is highly similar in chemical structure to the neuromodulator serotonin (as mentioned previously), and both compounds can be chemically derived from the trace amine tryptamine, which in turn can be derived from the essential amino acid tryptophan — in fact, DMT appears to be of lesser molecular complexity than even tryptamine itself, as well as all other psychedelics, suggesting that its evolutionary presence in the human body may predate that of serotonin (Gallimore, 2013: 485–486, 488, 495). Moreover, pure DMT appears to be neuropharmacologically unique in the sense that, out of all psychedelics, its duration of action is the most brief, its subjective intensity relative to dosage is the most extreme, and its metabolism and subsequent clearance from the brain is the most rapid — which would be expected if DMT were a neurotransmitter (Gallimore, 2013: 486–487). In addition, it has been shown that DMT is actively accumulated and selectively compartmentalised in the brains of rats and dogs, which enables the possibility of its release into specific brain regions at specific times — as is the case with neurotransmitters — and it is plausible that a similar mechanism exists in humans, due to neuroanatomical similarities (Gallimore, 2013: 487; Wallach, 2009: 94; Yanai et al., 1986: 141). Furthermore, DMT is unlikely to be a neurohormone (the only other type of neural signal carrier): essentially, neurohormones are nonselective (i.e bind indiscriminately to all receptors that they are chemically capable of binding to), whilst neurotransmitters are selective (i.e. bind to specific receptors), and DMT is certainly selective (Wallach, 2009: 92). Accordingly, and taking into account the plausibility that DMT is an endogenous ligand of the TAAR6 receptor, it is highly plausible that DMT is an endogenous neurotransmitter — and given its unique neuropharmacological and neurotransmitter-like properties, it is highly plausible that DMT does indeed have a natural neurobiological function directly or indirectly related to sensory perception.

However, endogenous DMT has never been empirically observed in the human body above trace concentrations, let alone those sufficient to produce alterations in sensory perception (Gallimore, 2013: 491–492). For this reason and the fact that endogenous DMT still naturally occurs at high concentrations in numerous plant and animal species, a somewhat speculative, yet at the same time evidentially compelling hypothesis has been proposed by Gallimore (2013: 491–494): that DMT is an ancestral neuromodulator, whose functional significance and endogenous concentration levels in humans have gradually decreased with the progression of evolution. The fundamental premise of this hypothesis is that whilst the thalamocortical system has developed the stable consensus world-representation through the course of evolution under the regulation of serotonin and modulation by external information, the thalamocortical system has also developed an altogether separate, equally stable ‘breakthrough’ world-representation, except that the latter took place under the regulation of endogenous DMT (Gallimore, 2013: 488–491). Accordingly, on the ‘ancestral neuromodulator’ hypothesis, the repertoire of thalamocortical states that is expressed at any given time depends on whether the 5-HT2A-5-HT1A activation balance in the cortex is currently controlled by serotonin or DMT, which also explains why the consensus world is now perceived as a default state: endogenous DMT is no longer present in humans above trace concentrations, unlike serotonin (Gallimore, 2013: 481, 488–491). However, in order for this to even be a logical possibility, it must first be shown that the worlds neurally represented in DMT states, at any phenomenological level, could be modulated by external information — otherwise, there is no reason to accept that a separate, ‘breakthrough world’ repertoire of thalamocortical states had ever been developed in addition to the ‘consensus world’ repertoire.

The capacity of the human brain to generate world representations without any external informational input, entirely through internal thalamocortical activity — using the same repertoire of thalamocortical states that represent the consensus world — is most clearly exemplified by dream states (Gallimore, 2013: 465–466, 482). This has been empirically substantiated through the observation that dream states and ordinary waking consciousness are phenomenologically continuous — in particular, that both dream states and ordinary conscious states can and often do exhibit the same types of events and activities that comprise their perceptual content, that the duration of those activities tends to be proportionately similar, and that the functionality of the sensory modalities in dream states is not significantly dissimilar to that of ordinary conscious states (Kahan & LaBerge, 2011: 494; Schredl & Hofmann, 2003: 298). `Therefore, if the DMT world-representation is not modulated by any external information, it must to some degree be phenomenologically comparable to the repertoire of thalamocortical states that represents dream worlds and the consensus world. However, DMT worlds at the ‘breakthrough’ level are “utterly incomparable” in phenomenal character to either dream worlds or the consensus world — instead, ‘breakthrough’ worlds seem to be represented by an altogether different, highly stable repertoire of thalamocortical states, evidenced both by their phenomenological ‘alienness’ and cross-commonality (Gallimore, 2013: 481–483). Accordingly, if ‘breakthrough’ worlds are phenomenologically incomparable to dream worlds or the consensus world, as well as exhibit phenomenological ‘alienness’ and cross-commonality, this entails that ‘breakthrough’ worlds are expressed through a repertoire of thalamocortical states that is stable and altogether different to the ordinary repertoire, which means that the ‘breakthrough’ repertoire cannot be modulated entirely through internal thalamocortical activity, leaving only one possible option as to how the ‘breakthrough’ repertoire could have been developed: by being modulated by external information (Gallimore, 2013: 483–484). Therefore, at least at the ‘breakthrough’ level, the worlds neurally represented in DMT states must be modulated by external information and thus the ‘ancestral neuromodulator’ hypothesis remains plausible.

Furthermore, on the ‘ancestral neuromodulator’ hypothesis, these two different repertoires were developed in a diurnal cyclic pattern — the ‘consensus world’ repertoire during the day and the ‘breakthrough world’ repertoire during REM sleep — resulting in their “parallel neural evolution”, which is consistent with the observation that serotonin concentrations in the human brain decrease during REM sleep, during which an increase in endogenous DMT concentrations presumably took place instead — until this presumably no longer conferred an adaptive advantage, resulting in an evolutionary decrease of endogenous DMT concentrations in humans (Gallimore, 2013: 493–494; McCarley, 2007: 302). Although the nature of this presumed adaptive advantage remains an open question, it has been proposed that the ancestral practice of the exogenous ingestion of DMT-containing plants may have served as a catalyst for the evolutionary development of the capacity of imagination in the human brain, which may indeed reflect the presumed evolutionary function performed by the ‘breakthrough world’ repertoire — a function which could thus have been related to the envisioning (via imagining) of possibilities such that the foresight necessary for better environmental adaptation or survival could be developed, for example (McKenna, 1992: 19).

In addition, since information processing is more complex and more efficient during sleep than waking, this may explain why the ‘breakthrough’ world appears highly complex and hyperadvanced compared to the consensus world — their respective representations may have developed at vastly different rates, reflecting this difference (Giuddia, 2010: 226; Wagner, Gais, Haider, Verleger, & Born, 2004: 352). The plausibility of the ‘parallel neural evolution’ model is further increased by the fact that the biosynthesis (i.e. endogenous production) of melatonin (also a chemical derivative of tryptamine) in the human pineal gland takes place only during darkness and thus follows the same diurnal pattern — and since it has been observed that DMT is actively biosynthesised in the rodent pineal gland and that the human pineal gland indeed contains the enzymes necessary for DMT biosynthesis, it is plausible that DMT biosynthesis in higher-than-trace concentrations in humans took place in the pineal gland and had been gradually replaced by melatonin over the course of evolution (Barker, 2018: 13; Gallimore, 2013: 494).

In effect, is it plausible that the natural neurobiological function of DMT, if it is indeed an endogenous neuromodulator is to trigger and sustain the transition from the ‘consensus world’ repertoire to the ‘breakthrough world’ repertoire of thalamocortical states (and perhaps the activation of the TAAR6 receptor by DMT constitutes the initial triggering mechanism, if DMT is indeed its endogenous ligand) — an ancestral function whose neurobiological necessity gradually became obsolete with the evolutionary developments in conscious perception, theoretically resulting in a gradual decrease of endogenous concentrations of DMT in humans. This is consistent with the theoretical proposal by Carhart-Harris that psychedelics have an ‘entropic’ effect on conscious states, in the sense that psychedelic states resemble ancestral conscious states that are in theory ‘entropic’: characterised by higher sensitivity to external information and thus both lower minimisation of sensory prediction errors as well as a wider range of typically expressed thalamocortical states than modern conscious states that are ‘negentropic’ (i.e entropy-suppressing) (Carhart-Harris et al., 2014: 7, 13; Carhart-Harris et al., 2016: 4858; Gallimore, 2013: 492). Accordingly, the weak internalist position does not require the ‘breakthrough’ world-representation to be modulated by external information from an alternate reality, but only so from the same consensus reality through which the consensus world-representation was developed, nor does it require external information to be received in real-time during ‘breakthrough’ experiences, but only so that this had occurred at some point in evolution. Thus, on this view, the informational sources of these two world-representations are not necessarily metaphysically distinct (as externalism would claim), but could rather have been the same one source — our consensus reality at different evolutionary stages of conscious perception, which thus provides an internalist explanation for both the phenomenal characteristics and the phenomenal objectivity that characterise ‘breakthrough’ experiences and without their dismissal as simply ‘elaborate hallucinations’ (Gallimore, 2013: 494, 498). Thus, according to weak internalism, at dosages sufficient to occasion ‘breakthrough’ experiences, DMT is indeed capable of ‘channel-tuning’, in the sense that it facilitates a shift between two different world-representations, and because both of these representations were on this view developed by the brain through the course of evolution, this shift is fundamentally explainable through neurological facts, and therefore this is ultimately an internalist position.

Although somewhat speculative, the weak internalist position examined here greatly increases the explanatory power of the general internalist position — in particular, by providing plausible explanations for the endogenous presence of DMT in humans, its neurotransmitter-like properties, as well as its possible neurobiological function — without claiming that ‘breakthrough’ experiences are essentially illusory or misrepresentative and thus without contravening the majority opinion of psychedelic users, unlike strong internalism. Externalism (Part 3, below) follows the same trend, offering the greatest explanatory power at the expense of the least empirical substantiation out of the three positions examined in this paper.

3A. Epistemic access

The epistemic premise that underpins the externalist conception of the ‘channel-tuning’ thesis is that ‘breakthrough’ experiences facilitate epistemic access (i.e. the potential for the acquisition of knowledge) to information contained in an external dimension or reality which cannot be experienced in the state of ordinary waking consciousness, putatively evidenced by the traditional Amazonian shamanic function of communal integration of knowledge acquired through ayahuasca experiences (Frecska, 2018: 156).

In order to plausibly sustain the epistemic premise and qualify its externalist features, a distinction between two modes of epistemic access must first be made — the perceptual and the intuitive: the former denotes the traditional Western empiricist method of acquiring knowledge objectively, by observation of external reality through the sensory modalities, and the latter denotes the traditional Eastern spiritualist method of acquiring knowledge through pure conscious experience, without sensory processing — best exemplified by meditation (Frecska, 2018: 156, 163–165; Jung, 1972b: 383; Reddy, Pereira, de Souza Leite, & Roy, 2020: 1). Furthermore, knowledge acquired perceptually can most of the time be expressed linguistically and is therefore linguistically transferable (such as the mathematical relation between force, mass, and acceleration), whereas knowledge acquired intuitively is purely experiential and thus always nonlinguistic — and therefore not linguistically transferable (such as the concept of ‘redness’) (Frecska, 2018: 165). Accordingly, it has been theorised that these two modes of epistemic access resemble (metaphorically, at this stage), the two realms that fundamentally comprise physical reality — the local and the nonlocal, respectively: the former denotes physical reality that exists within the constraints of three dimensions of space and one dimension of time, and the latter denotes physical reality that exists beyond those spatiotemporal constraints — in the sense that, in order to acquire knowledge in the perceptual mode, knowledge-containing information must be localised in four-dimensional spacetime such that it can be processed through the sensory modalities, whereas in the intuitive mode, where knowledge-containing information bypasses the sensory modalities, directly manifesting in consciousness, this is presumably not required, on the psychedelic externalist view (Frecska, 2018: 155–156). Accordingly, the nature of the epistemic access that ‘breakthrough’ experiences facilitate on the externalist view is nonlocal, since the manner in which they confer perceived knowledge on users is subjective, the knowledge is purely experiential, and the ontological source of this knowledge appears to exist beyond the spatiotemporal constraints of ordinary physical reality, and this is the externalist nature of the epistemic premise (Frecska, 2018: 168).

As a result, it has been proposed that the exogenous administration of DMT may have performed a historical function to facilitate the acquisition of knowledge that enabled the creation of, inter alia, language, mathematics, and architecture — at the time when this knowledge would appear to greatly surpass the the progress of human civilisation — and this accords with the observation that the semantic content of ‘breakthrough’ experiences typically contains representations of knowledge whose complexity is seemingly incomprehensible in the state of ordinary waking consciousness or within the spatiotemporal constraints of ordinary waking reality, which on the externalist view thus suggests that such knowledge must originate from a nonlocal source (Kins, 2019; Psychedelic Community, 2020). Therefore, although highly speculative, it is certainly plausible that the putative historical examples of individuals acquiring knowledge nonlocally, supposedly through “divination” — which include, inter alia, Aristotle and Pythagoras — involved the ingestion of DMT-containing plants, similarly to the historical use of ayahuasca by indigenous Amazonian populations dating back at least as far as 1000 years ago, according to recent archeological evidence (Frecska, 2018: 166–167; Blakemore, 2019). Accordingly, this ‘exogenous’ proposal can be viewed as complementary to the weak internalist argument that endogenous DMT may have performed an evolutionary function, in the sense that the exogenous ingestion of DMT presumably performing a historical function of epistemic access could be viewed as an extension of the presumed evolutionary function performed by endogenous DMT (McKenna, 1992: 19). Therefore, on the externalist view, the semantic content and the epistemic feelings of lucidity and veridicality typically occasioned by ‘breakthrough’ experiences are not illusory (strong internalism) or even incidental (weak internalism), but epistemically valuable and functionally significant.

Although it is in principle impossible to provide specific examples of knowledge that has been or could be acquired through nonlocal epistemic access that ‘breakthrough’ experiences are presumably capable of facilitating due to the purely experiential, nonlinguistic nature of such knowledge, it is plausible that, in accordance with the putative examples and proposals above, ‘breakthrough’ experiences are capable of facilitating some level of epistemic access (the epistemic premise) from some other source, that the mode of this epistemic access is unlike the local mode which characterises empiricism, and that the local mode is not the only possible mode of epistemic access. Therefore, the epistemic premise cannot yet be rejected with certainty, which at this stage is arguably sufficient, because the extent of the plausibility of the epistemic premise ultimately depends on the extent of the plausibility of the metaphysical premise, which will examined in the section below.

3B. Quantum nonlocality

The metaphysical premise underpinning the externalist conception of the ‘channel tuning’ thesis is that the nonlocal realm of physical reality constitutes the ontological — not merely metaphorical — source of knowledge acquirable through nonlocal epistemic access and that this can grounded in naturalistic explanations (i.e. consistent with the natural sciences) (Frecska, 2018: 156; Papineau, 2020). On the psychedelic externalist view, this premise can be grounded in one of the interpretations of quantum mechanics, metajustified by the fact that the mathematical validity of its principles has been confirmed by numerous experiments — indeed, there is a consensus among physicists that one of the interpretations of quantum mechanics must be true, though which interpretation that is remains a matter of debate (Williams, 2016: 329).

To begin, the quantum-mechanical principle of entanglement denotes that an interaction between two or more subatomic particles creates a mutual correlative relation (a ‘quantum correlation’) between their quantum states (defined by spin and orbital angular momentum), which in turn gives rise to the phenomenon of quantum nonlocality, which has indeed been empirically observed: whenever a change occurs in the quantum state of one of the entangled particles, an opposite change occurs in the quantum state of the other(s) — instantaneously, or seemingly so — irrespective of the local physical distance between them and thus unconstrained by the four-dimensionality of local physical reality, suggesting that the nature of this connection between entangled particles is nonlocal (Commissariat, 2015; Frecska, 2018: 156–158; Shute, 2019: 8–9; Williams, 2016: 340). Thus, on the externalist conception of the ‘channel-tuning’ thesis, ‘breakthrough’ experiences somehow enable the brain to function as a ‘quantum antenna’ that facilitates real-time reception of semantically coherent and epistemically valuable information from the nonlocal realm (Frecska, 2018: 156). Accordingly, on the externalist view, by presumably facilitating the reception of information from the nonlocal realm, ‘breakthrough’ experiences enable conscious states to be modulated by nonlocal information — resulting in veridical, yet seemingly ‘alien’ perceptual content — and therefore, ‘breakthrough’ phenomenology is directly ontologically dependent on external factors (Frecska, 2018: 161). Therefore, the exact point of divergence between the externalist and the weak internalist conceptions of the ‘channel-tuning’ thesis is that the externalist considers the difference between the two ‘channels’ — ‘consensus reality’ and ‘breakthrough experience’ — to be metaphysical, not merely evolutionary, in the sense that these two channels represent metaphysically distinct realms of physical reality, not the same realm at different evolutionary stages.

The externalist conception of the ‘channel-tuning’ thesis is fundamentally premised on the proposal that, in addition to the informational structure of internal brain activity being characterisable by fractality (as explained in Section 2B), the physical structure of the brain may also be fractal — which is certainly plausible given the fact that fractality characterises both the physical structure of the universe as well as numerous physiological structures of biological organisms, including those of humans, best exemplified by the sequential branching of blood vessels and bile ducts, suggesting that all physical reality may be fundamentally fractal in structure, resembling a holographic projection (Hameroff, 2020; Hameroff & Penrose: 2014: 46; Walling & Hicks, 2003: 163). Accordingly, if the brain's physical structure is indeed fractal, in addition to its informational structure, their scale-free structural self-similarity would in principle enable the brain to ‘shift’ from the ‘default’ neuronal level to various other levels in the physical-informational fractal hierarchy, including the quantum level — such that it would then presumably be possible to receive nonlocal information, which would in turn enable the brain to represent the external world via novel, yet still veridical conscious states — and this is what happens during ‘breakthrough’ experiences, whose fractal spatial geometry thus constitutes a veridical representation of the fundamental geometry of physical reality, on the externalist view (Frecska, 2018: 161; Hameroff, 2020). The externalist reason why the external world is represented by neuronal-level processes and in four dimensions by default is that the resulting conscious states are modulated by external information that is exclusively local and are thus ‘negentropic’ in nature (in the same sense as conceived by weak internalism) — they effectively minimise environmental prediction errors (Frecska, 2018: 162). Furthermore, on the externalist view, ‘shifting’ to the quantum level such that conscious states become modulated by nonlocal information allows for the possibility of facilitating real-time nonlocal epistemic access — a function that is, or may have naturally performed by endogenous DMT, which could be seen as an extension of the world-representation switching function proposed by weak internalism (Frecska, 2018: 163).

It follows to examine whether quantum mechanics is at least in principle consistent with the metaphysical premise of psychedelic externalism — that the nonlocal realm of physical reality, by virtue of which quantum nonlocality is possible, constitutes the ontological source of the knowledge acquirable through nonlocal epistemic access. There are two types of interpretations of quantum mechanics that may allow, at least in principle, the possibility of conscious states being modulated by nonlocal information such that — in line with the metaphysical premise — this could facilitate epistemic access that is ontologically, not merely metaphorically, ‘nonlocal’: interpretations based on the principle of entanglement and interpretations based on the concept of potentiality (i.e. an ontocosmological substratum posited as the metaphysical ground for all existence) (Williams, 2016: 336). According to entanglement-based interpretations, nonlocal information is contained in quantum correlations formed between entangled subatomic particles (Frecska, 2018: 156). One such interpretation is provided by the Orchestrated Objective Reduction theory, according to which conscious states emerge from patterns of quantum correlations between oscillation-coherent collections of subatomic particles sustained by microtubules (i.e cylindrical structures constituted of protein) within neurons and coherent collections of subatomic particles in the external environment, which entails that the brain and the external environment have a symbiotic quantum relationship (Emilsson, 2016a; Frecska, 2018: 160–161; Hameroff & Penrose, 2014: 39; Williams, 2016: 340). Thus, on this view, during ‘breakthrough’ experiences, the internal quantum processes that determine the manner in which the brain receives external information are altered such that conscious states become modulated by novel patterns of quantum correlations between the brain and the external environment, resulting in the reception of novel — ‘nonlocal’ — information, and this is how nonlocal epistemic access presumably occurs (Emilsson, 2016a).

However, it has been objected that entanglement-based interpretations are inherently based on dubious assumptions. The first assumption is that it is possible for quantum correlations to be sustained between subatomic particles and macroscopic objects — in this case, neurophysiological structures called microtubules — which contravenes the consensus in quantum mechanics that the entanglement of subatomic particles with macroscopic objects triggers rapid decoherence, and because oscillation coherence is necessary to sustain quantum correlations, it is unlikely that quantum correlations between external subatomic particles and neurophysiological structures can be sustained, and therefore, neither can the transmission of nonlocal information into the brain (Williams, 2016: 340–341). It has been argued in response that coherence between external subatomic particles and neurophysiological structures is a mathematical possibility, which entails the possibility of transmission of nonlocal information into the brain (Hagan, Hameroff, & Tuszynski, 2000: 1). However, even if this is true, entanglement-based interpretations are based on another dubious assumption: that the brain is somehow able to receive semantically coherent nonlocal information from quantum correlations — which is, again, unlikely, since this requires coherent collections of subatomic particles large enough to generate semantically coherent nonlocal information to exist in inherently non-coherent natural local external environments, which has never been previously demonstrated (Williams, 2016: 342). Therefore, it seems unlikely that entanglement-based interpretations can plausibly accommodate the possibility of conscious states being modulated by nonlocal information such that nonlocal epistemic access would be possible — and thus unlikely that the metaphysical premise of psychedelic externalism could be plausibly sustained though entanglement-based interpretations of quantum mechanics.

In any case, potentiality-based interpretations of quantum mechanics appear more successful in accommodating the possibility of ontologically nonlocal epistemic access. One such explanation is provided by Bohm's Implicate Order theory, which posits an ontocosmological state space (the ‘implicate order’) comprised entirely out of neutral (i.e. neither physical nor mental), nonlocal information (‘active information’) that contains all possible manifestations of reality — ‘potentialities’ — and determines the outcome states of all aspects of manifested, observable reality (the ‘explicate order’) both at the subatomic and the macroscopic scale, which thus constitutes the ontological source of both consciousness and physical matter and serves as a metaphysical ‘bridge’ between them (Bohm & Hiley, 1993: 384; Williams, 2016: 332, 342–344). Accordingly, the Implicate Order theory suggests that the mental and the physical aspects of observable reality (the ‘explicate order’) are metaphysically reflexive — their existence is reflected and constituted by the same neutral fundamental state space (the ‘implicate order’) (Bohm & Hiley, 1993: 384).

In order to explain the phenomenon of quantum nonlocality in the first place, potentiality-based interpretations claim that physical reality, at its most fundamental level of ‘potentiality’, must be extra-dimensional — existing in more than the three spatial dimensions and one temporal dimension that comprise local physical reality — because, on Bohm's view, the contradictory relation between quantum nonlocality and theories of local physical reality (e.g. theory of relativity) suggested the existence of an extra-dimensional, nonlocal realm of physical reality from which both quantum reality and local physical reality emerge (Williams, 2016: 347). Accordingly, the spatiotemporal extra-dimensionality of the potentiality realm provides an externalist explanation of the perceived extra-dimensional structure of ‘breakthrough’ experiences, as well as the element of hyperadvancement present in some of the perceptual content of those experiences, which on this view constitute quasi-veridical representations of the spatiotemporal possibilities that could manifest from potentiality — ‘quasi-’ due to the element of possibility rather than actuality.

In respect to accommodating the possibility of ontologically nonlocal epistemic access, potentiality-based interpretations effectively circumvent the problems relating to quantum coherence faced by entanglement-based interpretations: by proposing that the ontological source (in this case, the ‘implicate order’) of nonlocal information is metaphysically distinct from and prior to the quantum-mechanical realm in which entanglement occurs, potentiality-based interpretations render quantum coherence irrelevant in determining whether nonlocal information can manifest in consciousness (Williams, 2016: 343). However, the question remains as to how conscious states could be modulated by nonlocal information that exists in an ontocosmological realm such that nonlocal epistemic access would be possible. Following the Implicate Order theory, both consciousness and physical matter emerge from the same neutral realm of potentiality, whose fundamental constituent — ‘active information’ — is both inherently probabilistic in nature and possesses proto-conscious properties that serve as precursors to conscious states, aimed to accommodate both consciousness and physicality, which entails some form of neutral monism (i.e. the view that the fundamental constituents of reality are neither entirely mental nor physical but instead possess or constitute both properties) (Pereira, Nunn, Pregnolato, & Nixon, 2018: 189; Williams, 2016: 346–347). Thus, on this view, during ‘breakthrough’ experiences, the patterns of ‘active information’ that manifest in consciousness are altered such that the state space of the phenomenal possibilities encoded by ‘active information’ that could manifest in consciousness is significantly expanded, and since a greater range of phenomenal possibilities entails a greater range of experiential knowledge that can be acquired from the realm in which all nonlocal information is contained, this constitutes nonlocal epistemic access. Moreover, an increase in the range of the phenomenal possibilities that could manifest in consciousness also provides an externalist explanation of how the phenomenal characteristics of ‘breakthrough’ experiences originate — they are an expansion of the state space of the possible conscious states that could manifest (Pereira et al, 2018: 195; Shute, 2019: 19; Williams, 2016: 343). However, at this stage, this explanation is far from naturalistically acceptable and mirrors the strong internalist ‘hyperintegration’ model albeit at a far lower level of detail — and therefore requires further substantiation as well as interpretive qualification if this explanation is to provide any plausible ground for the metaphysical premise of psychedelic externalism.

Specifically, and taken together, the posited proto-conscious properties and probabilistic nature of ‘active information’ aim to accommodate the quantum-mechanical principle of wave-particle duality — that subatomic particles exhibit both wave-like and particle-like characteristics — which gives rise to the phenomenon of wave-particle collapse famously observed in the ‘double-slit’ experiment, in which subatomic particles exhibit probabilistic, wave-like behaviour before their quantum state is measured, but upon measurement, their probabilistic, wave-like state appears to collapse into a localised, particle-like state (Gardiner, 2015: 30). In turn, the phenomenon of wave-particle collapse gives rise to the still unresolved Measurement Problem: identifying the exact causal basis for wave-particle collapse and the relevance of consciousness in this phenomenon — since there is nothing to suggest how a physical measuring apparatus, being comprised of the same subatomic particles as those under observation, could instigate wave-particle collapse absent of conscious intention to make a measurement (Arvan, 2019: 349–350; Williams, 2016: 329). In response to the Measurement Problem, the Implicate Order theory suggests that conscious intention causally affects the nonlocal field of ‘active information’ that in turn determines both the physical outcome states and the conscious states that observe them, which requires ‘active information’ to have both probabilistic and proto-conscious features (Williams, 2016: 331, 344). As a result, on Bohm's view, physicality and consciousness are equally fundamental properties, suggesting that consciousness is not an emergent, but an intrinsic property of the fundamental constituents of reality, which entails non-reductive physicalism — the view that consciousness is conceptually irreducible to purely physical (or material) constituents — a view that is rather controversial under the current materialist paradigm in the natural sciences (Papineau, 2020; Shute, 2019: 10–11). Although the Implicate Order is thus an unorthodox interpretation of quantum mechanics under the current materialist paradigm, being a theory that is non-reductive and thus one that is considerably difficult to verify experimentally, it has been prospected that in order to conclusively resolve both the Measurement Problem and the Hard Problem of Consciousness, a shift away from the materialist paradigm might be necessary, suggesting that it may be too early to dismiss potentiality-based interpretations of quantum mechanics as implausible altogether (Shute, 2019: 15–18; Williams, 2016: 346–347). However, this does not constitute a positive naturalistic ground for the metaphysical premise of psychedelic externalism about nonlocal epistemic access, which means that from a naturalistic perspective, this premise cannot be sustained, at least under the current materialist paradigm. Accordingly, I will henceforth attempt to determine the extent to which the concept of a neutral dimension of potentiality is even conceptually justified as an explanatory basis for psychedelic externalism, which follows in the section below.

3C. Transpersonal consciousness & potentiality

If we accept that individual conscious agents and the presumed proto-conscious constituents of fundamental reality are indeed metaphysically reflexive, as the Implicate Order theory suggests, this allows, at least conceptually, for some form of nonlocal, transpersonal consciousness to be emergent from this proto-conscious field of fundamental constituents and in principle accessible by individual conscious agents, given the element of metaphysical reflexivity (Pereira et al. 2018: 195–196; Shute, 2019: 1, 11; Williams, 2016: 343). Although the concept of a transpersonal consciousness is, again, controversial under the current materialist paradigm, this concept may be useful in providing an externalist explanation based on the concept of potentiality beyond mere determinism about ‘active information’ as to how ‘breakthrough’ experiences could have a common phenomenology as well as facilitate the reception of both epistemically valuable and semantically coherent information from the nonlocal realm (Kastrup, 2018: 41; Williams, 2016: 343). Accordingly, whether the psychedelic externalist position based on the concept of potentiality is even marginally plausible could be more accurately ascertained by examining the extent to which the concept of a transpersonal consciousness is indeed explanatorily powerful in respect to ‘breakthrough’ experiences, as well as naturalistically acceptable.

One specific theory of a transpersonal consciousness that is conceptually consistent with the Implicate Order theory is Jung's (1972a, 1972c) Collective Unconscious model — whose shared characteristics include a posited ontocosmological dimension of possibilities, the element of metaphysical reflexivity, as well as the possibility of nonlocal mental connections — indeed, it has been suggested that these two theories essentially differ only linguistically, not metaphysically (Gardiner, 2015: 31; Shute, 2019: 12, 15–18). In particular, the Collective Unconscious model provides an explanatory mechanism of the metaphysical reflexivity between a transpersonal consciousness and individual conscious agents, which, as will be discussed, yields a useful externalist framework through which ‘breakthrough’ experiences can be interpreted. After outlining the model, I will examine the extent to which it enhances the explanatory power of psychedelic externalism, after which I will discuss an alternative, internalist interpretation of the model, and then evaluate the strength of the externalist position.

The first premise of Jung's model is that the mental content of an individual conscious agent is partitioned into two structures — the conscious and the unconscious: the former contains the mental content of an individual conscious agent of which that agent is actively aware, which functions to sustain continuous environmental adaptation and survival, and the latter contains the mental content of an individual agent that has been repressed, forgotten, processed through the sensory modalities without manifesting in consciousness, as well as the content that is yet to manifest in consciousness (Adamski & Borowik, 2014: 86–87; Jung, 1972a, 173–176; Jung, 1972b: 151). In addition to conscious and unconscious content at the individual level, Jung posits the ‘collective unconscious’: a transpersonal-level structure conceived as a heritage common to all individual conscious agents that contains all mental content that has manifested or could possibly manifest in individual consciousness, on which all individual-level mental content supervenes and with which the individual-level unconscious content has a metaphysically reflexive information-exchanging relationship, but which is directly inaccessible in the state of ordinary waking consciousness (Adamski & Borowik, 2014: 86–87; Jung, 1972b: 152; Mills, 2019: 40; Shute, 2019: 5). Furthermore, the collective unconscious is taken by Jung to indirectly manifest in ordinary waking reality in the form of ‘archetypes’ — symbols commonly reoccurring throughout human history, typically encountered in dreams, mythology, and art (Jung, 1972b: 213; Shute, 2019: 6). In addition, the collective unconscious is conceived as capable of being directly — consciously — experienced but not consciously controlled, through “numinous experiences” such as transcendental dreams, characterised by feelings of metaphysical continuity with a consciousness that seemingly extends beyond the metaphysical boundaries of an individual mind — a ‘transpersonal’ consciousness (Shute, 2019: 6–7).

Taken together, the elements of indirect manifestation via archetypes, the possibility of direct yet uncontrollable experience, and the metaphysical reflexivity between the individual unconscious and the collective unconscious provide an effective — yet at this stage, still non-naturalistic — explanatory framework for the externalist position on ‘breakthrough’ phenomenology. Accordingly, based on this framework and in line with psychedelic externalism, ‘breakthrough’ experiences can be interpreted as a direct, uncontrollable, numinous experiences of the collective unconscious, akin to transcendental dreams. This would explain why ‘breakthrough’ experiences seem to exhibit phenomenological cross-commonality and be accompanied by epistemic feelings of lucidity and veridicality: on this model, they facilitate access to a metaphysically objective, collectively shared state space of raw mental content-possibilities — the collective unconscious — at least some non-negligible part of which instantly manifests in consciousness during ‘breakthrough’ experiences, which can thus be interpreted as quasi-veridical, in the same way as interpreted in the context of the Implicate Order theory. Moreover, in the context of this framework, the ‘alien’ worlds, entities, semantic networks, and linguistic systems that form part of the perceptual content of ‘breakthrough’ experiences can be interpreted as the archetypal manifestations of the collective unconscious and thus conceived as stable, perceptual products of the continuous metaphysical reflexivity between the contents of the collective unconscious and the individual unconscious, but nevertheless as directly ontologically dependent on the collective unconscious — an external factor — not individual minds taken in isolation, since the mental contents of each individual mind, on this model, are metaphysically grounded in the contents of the collective unconscious (Frecska, 2018: 166–167). In turn, this also provides an externalist explanation of the representations of mind-independence about the metaphysical aspects of those experiences: these aspects are ontologically independent of the mind of each individual user, though presumably not independent of individual minds considered collectively, since the collective unconscious would presumably not exist if no individual minds ever existed. Furthermore, the representations of acquiring seemingly transhuman knowledge typically contained in ‘breakthrough’ experiences can be interpreted on this model as representations of the collective knowledge acquired throughout human history contained in the collective unconscious, whose epistemic status is presumably modulated by the same reflexive relationship — between the individual unconscious and the collective unconscious, which in effect provides a possible yet non-naturalistic metaphysical mechanism behind nonlocal epistemic access to information that is both epistemically valuable as well as semantically coherent (Adamski & Borowik, 2014: 87).

Thus, taken together, the Implicate Order and the Collective Unconscious are able to provide an interpretively comprehensive externalist account of ‘breakthrough’ phenomenology, addressing each of its aspects as outlined in Part 1 — yet, this dual framework, at least currently, seems to be only marginally more naturalistic than Buddhist cosmology, so are such ontocosmological models even necessary? Not so, according to internalism, which claims that such ontocosmological models commit the fallacy of misplaced concreteness — by unnecessarily granting the status of metaphysical actuality to abstract concepts almost equivalent, if not equivalent, to the concept of infinity, such as ‘potentiality’ and the ‘collective unconscious’ (Mills, 2019: 43, 51). Furthermore, on the internalist view, the concept of a collective unconscious could simply be reinterpreted as an abstract entity that consists of the neuroanatomical structure and mental content that are universally shared among individual conscious agents — a ‘universal unconscious’ — without the need to propose that those contents and structures form a collective metaphysical entity whose existence extends beyond the boundaries of individual brains (Mills, 2019: 40, 44, 46). Therefore, according to internalism, it is not necessary and thus parsimoniously undesirable to invoke non-naturalistic externalist metaphysics in order to explain the universality of some aspects of conscious experience — whether altered states of consciousness such as ‘breakthrough’ experiences or the state of ordinary consciousness. Nevertheless, weak internalists have expressed support for the idea that psychedelics may indeed be uniquely capable of accessing unconscious mental content at the individual level and that therefore, the ‘universal unconscious’ could constitute a significant ontological factor in ‘breakthrough’ phenomenology, though the plausibility of this speculation can only be more accurately ascertained with the future progress in the empirical research into the unconscious — for which psychedelics may thus perhaps prove useful (Carhart-Harris et al., 2014: 18; Gallimore, 2013: 494–495).

According to externalism, however, as speculative and non-naturalistic as ontocosmological models of such as the Implicate Order and the Collective Unconscious may appear to internalists, such models are indeed necessary because they at least attempt to define the ontological source of phenomenality — conscious experience itself — something that neural-level internalist models of consciousness, which merely explain the ontological origin of perceptual content — do not accomplish, and are therefore arguably no closer to resolving the Hard Problem of Consciousness than externalist models (Pereira et al., 2018: 194). Moreover, there have been sophisticated — yet at this stage, still not entirely naturalistic — attempts at grounding a potentiality-emergent transpersonal consciousness in naturalistic explanations, one such model having been proposed by Pereira et al. (2018) based on both classical and quantum physics and another having been proposed by Adamski and Borowik (2014) based on quantum physics alone. However, I do not take this to be sufficient evidence in respect to plausibly sustaining the psychedelic externalist claim that ‘breakthrough’ experiences facilitate epistemic access that is ontologically nonlocal, although I do assert that potentiality-based psychedelic externalism cannot yet be conclusively rejected, because conceptually — but only conceptually — this position provides an interpretively comprehensive account of ‘breakthrough’ experiences that does not seem to fare worse, if at all, than the internalist accounts. Furthermore, I assert that the externalist position cannot yet be conceived as inherently non-naturalistic, since a naturalistic explanation of the origin of phenomenality — which would settle the matter conclusively, or nearly so — remains elusive. Accordingly, there is at least some marginal possibility — but currently, not any more than that — that externalism could turn out to be a more favourable position in respect to psychedelic phenomenology as future progress in consciousness research and quantum mechanics is made.

Nevertheless, because psychedelic externalism requires the acceptance of numerous assumptions that have not yet been grounded in naturalistic explanations to any extent close to sufficient, I assert that this position is currently the least favourable out of the three examined in this paper. This leaves strong and weak internalism as canditates for the most favourable position. Based on the examination of these positions in this paper, the weak internalist position appears more favourable. Perhaps most importantly, weak internalism, unlike strong internalism, addresses the endogenous presence of DMT in humans, whose natural neurobiological function remains an empirical mystery yet to be settled conclusively: a mystery that weak internalism uniquely and arguably more than speculatively, albeit not entirely conclusively, attempts to resolve by incorporating more recent, relevant neuropharmacological research into its explanatory framework than strong internalism — in particular, the discovery of the trace amine receptor class — which yields an interpretive account of ‘breakthrough’ experiences that not only extends deep into evolution, but also one that is consistent with the overwhelming majority opinion of the psychedelic community, that ‘breakthrough’ experiences are not simply ‘elaborate hallucinations’ essentially characterised by perceptual misrepresentation and illusory mental content, unlike strong internalism. Moreover, weak internalism addresses the Phenomenal Objectivity Question with far greater explanatory power — by proposing that ‘breakthrough’ phenomenology is indeed in some sense objective, or universally shared — without invoking speculative, largely non-naturalistic externalist metaphysics and without dismissing the element of cross-commonality unique to ‘breakthrough’ phenomenology as simply an illusion created by the universally shared evolutionary development of metacognition, an explanation otherwise proposed by strong internalism that appears far more dismissive than comprehensive. Therefore, I assert that the weak internalist position on psychedelic phenomenology is to be favoured over the strong externalist and that both internalist positions are to be favoured over the externalist — unless and until further research in consciousness and quantum mechanics demonstrates that the externalist position can be unambiguously grounded in naturalistic explanations.