1/18 THREAD. New paper by @marcoaqil and me. We challenge most theories regarding the neural basis of psychedelic action by claiming something quite simple: psychedelics are visionary and most theories don’t take this specific sensory domain into account. sciencedirect.com/science/articl…
2/18 Most neuroscientific models take conceptual inspiration from Huxley's “reducing valve” hypothesis , and the historical qualifications of psychedelics as generic “mind-manifesting”, or “nonspecific amplifiers”, or “meaning-enhancing”, or “suggestibility-inducing” substances.
3/18 These nonspecific frameworks do not take into account that, particularly in the visual domain, psychedelic phenomenology presents highly specific characteristics, as such, the psychedelic-induced visionary state cannot easily be captured as a nonspecific amplification.
4/18 In recent years the field moved away from the historically-charged and negatively-laden ‘hallucinogenic’ characterization and towards the more positively-laden psychedelic, entheogenic or neuroplastogenic characterizations
5/18 We propose that this move is throwing out the baby with the bathwater, and leads to a scientific neglect of the most obvious effect of psychedelics.
6/18 The two most popular theories re psychedelic mechanism of action - REBUS (relaxed top-down beliefs) and CSTC (relaxed thalamic gating) - do not explain why psychedelics are specifically visual.
7/18 The phenomenology of psychedelic visionary states implies that they cannot simply be described as ‘nonspecific amplifications’ of ungated external sensory input, or unconstrained bottom-up prediction errors.
8/18 we review neuroimaging, pharmacology, questionnaires, & clinical studies, propose extensions to existing models, provide simulations of psychedelic-induced visual phenomena, and propose testable hypotheses for the potential therapeutic roles of visual hallucinations
9/18 we find that psychedelic-induced alterations in low-level sensory dimensions of experience are not entirely causally reconducible to alterations in high-level dimensions, but rather co-occur in a dialogical interplay with the latter,
10/18 and play a causally relevant role in determining high-level alterations and therapeutic outcomes.
11/18 Some details from the paper:
12/18 There is high distribution of 5-HT2a receptors in primary visual cortex and high level regions. Those in the primary visual cortex are probably in layer IV (input layer from LGN), unlike the rest of the cortex in which they are mostly in layer V
13/18 Psychedelics relate to enhanced activity in visual cortex , reduced alpha power, and enhanced connectivity between visual cortex and the rest of the brain
14/18 Visions are probably important therapeutically e.g, many insights emerge in a visual form. (the problem is that the questionnaires that measure visual aspects are not specific, and do not measure the valance of visions)
15/18 We conclude that integrating low-level and domain-specific aspects of psychedelic effects into existing models is a necessary step to improve the current understanding of how these substances effect both acute and long-term change in the human brain.
16/18 There is much more in the paper, go and check it out
17/18 Louis Lewin, Phantastica (1924): “Even if we consider this state as a hallucination of vision and perception, that is to say as a negation of reality, it conveys a real and #plastic life of the soul, like …. the so-called visionaries”
18/18 #Phantastica is a cool name for psychedelics/hallucinogens
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