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Serotonergic Hallucinogen-Induced Visual Perceptual Alterations

Profile image of FRanz X. VollenweiderFRanz X. Vollenweider

2016, Current topics in behavioral neurosciences

https://doi.org/10.1007/7854_2016_461
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Abstract

Serotonergic hallucinogens, such as lysergic acid diethylamide (LSD), psilocybin, and N,N-dimethyltryptamine (DMT), are famous for their capacity to temporally and profoundly alter an individual's visual experiences. These visual alterations show consistent attributes despite large inter-and intra-individual variances. Many reports document a common perception of colors as more saturated, with increased brightness and contrast in the environment ("Visual Intensifications"). Environmental objects might be altered in size ("Visual illusions") or take on a modified and special meaning for the subject ("Altered self-reference"). Subjects may perceive light flashes or geometrical figures containing recurrent patterns ("Elementary imagery and hallucinations") influenced by auditory stimuli ("Audiovisual synesthesia"), or they may envision images of people, animals, or landscapes ("Complex imagery and hallucinations") without any physical stimuli supporting their percepts. This wide assortment of visual phenomena suggests that one single neuropsychopharmacological mechanism is unlikely to explain such vast phenomenological diversity. Starting with mechanisms that act at the cellular level, the key role of 5-HT2A receptor activation and the subsequent increased cortical excitation will be considered. Next, it will be shown that area specific anatomical and dynamical features link increased excitation to the specific visual contents of hallucinations. The decrease of alpha oscillations by hallucinogens will then be introduced as a systemic mechanism for amplifying internal-driven excitation that overwhelms stimulus-induced excitations. Finally, the hallucinogen-induced parallel decrease of the N170 visual evoked potential and increased medial P1 potential will be discussed as key mechanisms for inducing a dysbalance between global

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What neural mechanisms underpin visual perceptual alterations from hallucinogens?add

The research identifies that 5-HT2A receptor activation plays a crucial role in mediating visual alterations, evidenced by animal studies correlating hallucinogenic effects with receptor affinity. Additionally, psilocybin notably decreases alpha oscillations, enhancing visual excitability, leading to distinctive visual hallucinations.

How do serotonergic hallucinogens affect early versus late visual processing?add

Findings indicate that hallucinogens enhance early visual processing, as indexed by increased P1 amplitude, while concurrently impairing late processing, evidenced by decreased N170 amplitude. This disruption is significant for tasks requiring global integration of visual stimuli.

What role does audiovisual synesthesia play in hallucinogen effects?add

Hallucinogens can induce synesthetic experiences, where auditory stimuli enhance visual perceptions. This effect relates to increased cortical excitability, yet requires further investigation to confirm mechanisms due to past methodological shortcomings.

How do subjective experiences differ among visual hallucinations?add

Hallucinogens create a continuum of experiences from imagery to vivid hallucinations, characterized by varying intensity and control. As dosage increases, subjects report difficulty in distinguishing between internally generated and externally induced percepts.

What historical insights inform modern understanding of hallucinogen-induced visuals?add

Early systematic analyses, like Klüver's work in the 1930s, identified consistent geometric patterns in visual experiences across subjects, termed 'form constants'. More recent studies expand on these findings, illustrating cross-cultural consistencies in reported visual phenomena.

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