Figure - available from: Frontiers in Psychology
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(A) Two-dimensional UMAP projection of all visual effect sentence embedding vectors. Each point corresponds to a single visual effect sentence, and colors denote different substances. The locations of some example sentences are indicated with arrows. (B) Illustration of visual effect categorization and calculation method. Seed sentences (listed in Table 3) were created to represent different regions of the visual effect vector space. Each visual effect was defined as the area within a threshold distance of a seed sentence vector. The proportions of visual effect sentences that fell within each category were then compared across substances. The black circles overlaid on the 2-dimensional point clouds demonstrate our procedure for categorizing visual effect sentences by calculating distances from seed sentence vectors (the center of each circle) and setting a distance threshold. Note that the analysis was conducted in the original 1,536-dimensional vector space, and the two-dimensional projection with overlaid circles/visual effect categories shown here is for illustration purposes.
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Introduction
Psychedelic compounds such as LSD, psilocybin, mescaline, and DMT can dramatically alter visual perception. However, the extent to which visual effects of psychedelics consistently vary for different substances is an open question. The visual effects of a given psychedelic compound can range widely both across and within individuals, s...
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Citations
... Similar types of distorJons are reported with serotonergic psychedelics. 20,[40][41][42] While largely anecdotal, limited psychophysical studies have explored some of these psychedelic phenomena systemaJcally. [43][44][45][46] Because visual distorJons depend on sensory sJmuli, they resemble classic visual illusions, 47 which can be studied using psychophysical modulaJon of sJmulus and task parameters. ...
... It is reported in ~25% of PD paJents 36 and is a hallmark of psychedelic experiences. 20,40,42 Convergent psychophysical evidence suggests the involvement of a specific perceptual process in both groups: impairments in higher-order, global-moJon integraJon but not lower-order, local-moJon processing. 49-51 This dissociaJon implicates middle temporal (MT) cortex, a region selecJve for higher-order moJon processing. ...
... Simple hallucinaJons, such as vivid geometric pa4erns, are a canonical SP-induced effect. 20,40,42 In contrast, they are rare in LBDs. 56 Moreover, these types of simple hallucinaJons are commonly the result of eye disease (i.e., Charles Bonnet syndrome), 57 which may be concurrent with LBD diagnoses. ...
Background and HypothesisVisual hallucinations (VH) are a core symptom of both Lewy body diseases (LBDs; e.g., Parkinson’s disease and dementia with Lewy bodies) and serotonergic psychedelics (SPs; e.g., psilocybin and mescaline). While these classes of VH differ in etiology, shared pathways are suggested by overlapping phenomenology and neural mechanisms. This review explores similarities and differences in VH between LBDs and SPs, focusing on phenomenology, cortical function, and serotonergic modulation.Study DesignThis narrative review synthesizes findings from neurology, cognitive neuroscience, and systems neuroscience to compare VH in LBDs and SPs. The literature includes studies with both human subjects and animal models that examine cortical activity patterns, neuromodulatory mechanisms, and VH phenomenology.Study ResultsBoth LBDs and SPs exhibit distinct visual aberrations, ranging from minor metamorphopsias to complex hallucinations. Specific classes of VH in LBDs resemble those induced by SPs (e.g., illusory motion and entity encounters), suggesting shared neural mechanisms. Neuroimaging studies indicate a common pattern of hyperactive associative cortex and hypoactive sensory cortex. At the neuromodulator level, SP-induced VH involves serotonin 2A and 1A receptor (5-HT₂AR and 5-HT₁AR) modulation, while in LBDs, 5-HT₂AR upregulation correlates with increased VH, and its inhibition (e.g., with pimavanserin) reduces VH. Two shared cortical signatures are highlighted: reduced visual evoked responses and shifts toward visual excitation.Conclusions
Examining cortical and neuromodulatory similarities between LBD- and SP-induced VH may elucidate the link between visual degradation, excitation, and hallucinogenesis. Future research should employ real-time neuroimaging of discrete hallucinatory episodes to identify shared mechanisms and develop targeted interventions for LBD hallucinations.
