A new neuroimaging study has revealed how the powerful psychedelic N,N-dimethyltryptamine, commonly known as DMT, alters the brain’s primary visual cortex, potentially explaining the intense visual distortions experienced by users. The findings, published in NeuroImage, suggest that DMT may significantly modify how visual information is processed in the brain, leading to phenomena such as blurred vision, tunnel vision, and the perception of expanded visual space.
DMT is a naturally occurring compound found in various plants and is known for producing brief but intense hallucinatory experiences. These experiences often involve vivid and sometimes overwhelming visual and auditory sensations. DMT belongs to the tryptamine class of psychedelics, which includes substances like psilocybin, the active compound in magic mushrooms, and 5-MeO-DMT. These compounds are chemically similar to serotonin, a neurotransmitter that plays a crucial role in regulating mood, perception, and cognition.
For centuries, cultures in South America have used DMT-containing plants in spiritual and religious rituals, most notably in the preparation of ayahuasca, a traditional psychoactive brew. In recent years, the scientific community has also become increasingly interested in these substances, not only for their ability to alter consciousness but also for their potential therapeutic benefits. Psychedelics like DMT are being studied for their efficacy in treating mental health conditions such as depression, post-traumatic stress disorder (PTSD), and anxiety.
The study, led by Marta Lapo Pais and her colleagues, aimed to explore how DMT affects the primary visual cortex, the area of the brain responsible for processing visual information. Specifically, the researchers wanted to test whether DMT alters the behavior of neurons in this region by changing their population receptive fields. Population receptive fields refer to the specific areas of the visual field that groups of neurons respond to. Under normal conditions, each cluster of neurons in the primary visual cortex is tuned to a particular area of the visual field.
The researchers hypothesized that DMT might cause these population receptive fields to expand or shift, leading neurons to respond to larger areas of the visual field or to areas they wouldn’t normally respond to. This alteration could explain the visual distortions reported by DMT users, such as the blurring of peripheral vision while central vision remains sharp—a phenomenon often described as tunnel vision.
To test this hypothesis, the researchers conducted a study with 11 healthy participants, including four women, with an average age of 37 years. These participants had experience with altered states of consciousness, particularly with DMT inhalation. Each participant underwent two neuroimaging sessions spaced several weeks apart.
During one session, the active treatment session, participants inhaled DMT extracted from the bark of Mimosa hostilis Benth., a tree native to South and Central America known for its high DMT content. The other session served as a control, where no DMT was administered.
In the active treatment session, participants inhaled between 50 and 70 milligrams of a substance containing approximately 31% DMT. Magnetic resonance imaging (MRI) was performed immediately after inhalation, capturing the peak effects of the drug. The imaging focused on the primary visual cortex, and the participants viewed a video of two perpendicular bars moving in specific patterns designed by the researchers. After the MRI, participants completed the Hallucinogen Rating Scale, a questionnaire that assesses the subjective effects of psychedelic substances.
The results showed that DMT significantly increased the population receptive fields of neurons in the primary visual cortex, particularly those that normally respond to the peripheral parts of the visual field. This increase suggests that DMT alters the way these neurons process visual information, which could account for the perceptual distortions such as peripheral blurring and tunnel vision.
Importantly, the study found no significant differences in eye or head movements between the DMT session and the control session, indicating that the observed changes were likely due to the effects of DMT on the brain rather than external factors.
“This evidence for short-term effects of DMT in pRF [population receptive fields] 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,” the study authors concluded.
The findings provide new insights into how DMT alters visual processing in the brain, offering a potential explanation for the intense and sometimes disorienting visual effects experienced by users. However, the researchers caution that the observed changes in the primary visual cortex are likely not the only neural alterations caused by DMT. Other regions of the brain, particularly those involved in higher-level visual processing, may also play a role in the complex visual phenomena induced by this psychedelic.
This study is an important step in understanding the neural mechanisms underlying the effects of DMT and other psychedelics. As research in this field continues to grow, these findings could have implications not only for our understanding of consciousness but also for the development of therapeutic applications for psychedelics in mental health treatment. However, further research is needed to explore the broader effects of DMT on the brain and to investigate how these changes relate to the subjective experiences reported by users.
The paper “Rapid effects of tryptamine psychedelics on perceptual distortions and early visual cortical population receptive fields” was authored by Marta Lapo Pais, Marta Teixeira, Carla Soares, Gisela Lima, Patr´ıcia Rijo, Celia Cabral, and Miguel Castelo-Branco.
