Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields.

Inhaled DMT, a psychedelic acting on 5-HT2A serotonin receptors, increases the size of neural population receptive fields (pRFs) in the peripheral visual field of the primary visual cortex (V1). This change, measured with MRI and pRF mapping in a within-subject design, occurred during visual effects documented by the Hallucinogen Rating Scale and was not explained by differences in eye or head movements. The enlarged pRFs may underlie perceptual distortions such as field blurring, tunnel vision, and enlargement of nearby visual space. The findings suggest that 5-HT2A receptor activation controls gain in visual cortex, linking neural population responses to psychedelic visual phenomena.

Study at a glance

Abstract

N, N-dimethyltryptamine (DMT) is a psychedelic tryptamine acting on 5-HT2A serotonin receptors, which is associated with intense visual hallucinatory phenomena and perceptual changes such as distortions in visual space. The neural underpinnings of these effects remain unknown. We hypothesised that changes in population receptive field (pRF) properties in the primary visual cortex (V1) might underlie visual perceptual experience. We tested this hypothesis using magnetic resonance imaging (MRI) in a within-subject design. We used a technique called pRF mapping, which measures neural population visual response properties and retinotopic maps in early visual areas. We show that in the presence of visual effects, as documented by the Hallucinogen Rating Scale (HRS), the mean pRF sizes in V1 significantly increase in the peripheral visual field for active condition (inhaled DMT) compared to the control. Eye and head movement differences were absent across conditions. This evidence for short-term effects of DMT in pRF may explain perceptual distortions induced by psychedelics such as field blurring, tunnel vision (peripheral vision becoming blurred while central vision remains sharp) and the enlargement of nearby visual space, particularly at the visual locations surrounding the fovea. Our findings are also consistent with a mechanistic framework whereby gain control of ongoing and evoked activity in the visual cortex is controlled by activation of 5-HT2A receptors.