This within-subject MRI study (n=11) finds that inhaled DMT increases the mean population receptive field (pRF) sizes in the peripheral visual field of the primary visual cortex (V1). Documented by the Hallucinogen Rating Scale (HRS), this effect explains visual perceptual distortions like field blurring and tunnel vision, and supports the role of 5-HT2A receptor activation in controlling visual cortex activity.
Abstract of Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields
“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.”
Authors: Marta Lapo Pais, Marta Teixeira, Carla Soares, Gisela Lima, Patrícia Rijo, Célia Cabral & Miguel Castelo-Branco
Summary of Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields
DMT is an indole alkaloid widely found in nature and is a psychedelic tryptamine associated with intense visual hallucinatory phenomena, perceptual changes and profound spiritual experiences. Psychedelic states induce changes in visual processing, including enlargement of nearby visual space, blurring and difficulty in focusing, with a bias for peripheral vision and visual distortions. These changes may be explained by changes in receptive field properties of cortical neurons.
Early visual areas can be mapped and delineated using functional magnetic resonance imaging (fMRI) retinotopic approaches. A model-driven approach, called the population receptive field (pRF) approach, has been proposed that estimates a neural response for each voxel that best explains the cortical visual field responses to a wide range of stimulus positions. Human studies investigating visual neuronal changes in pRF sizes are scarce. However, two clinical conditions with a visual phenomenon in common are autism spectrum disorder and glaucoma, which may explain the visual phenomenon induced by psychedelics: tunnel vision. We used pRF analysis to test the hypothesis that changes in population receptive field properties in the primary visual cortex (V1) might underlie visual distortions in psychedelic states, particularly at the visual periphery.
Methods
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https://doi.org/10.1016/j.neuroimage.2024.120718
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Cite this paper (APA)
Pais, M. L., Teixeira, M., Soares, C., Lima, G., Rijo, P., Cabral, C., & Castelo-Branco, M. (2024). Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields. NeuroImage, 120718.
Study details
Compounds studied
DMT
Topics studied
Neuroscience
Healthy Subjects
Study characteristics
Original
Open-Label
Within-Subject
Bio/Neuro
Participants
11
Humans
