Imagine closing your eyes and seeing vivid images as if your eyes were still open. This fascinating phenomenon is common during the ingestion of psychedelics like psilocybin, a substance found in certain “magic” mushrooms. In a new study published in the journal Molecular Psychiatry, scientists have used sophisticated imaging techniques to explore the neural underpinnings of these eyes-closed visual experiences, offering new insights into visual perception and imagery.
In recent years, psilocybin has gained attention for its potential therapeutic benefits in treating mental health conditions such as depression, anxiety, and post-traumatic stress disorder. The compound works primarily by activating serotonin receptors in the brain, leading to altered perceptions, enhanced mood, and profound changes in consciousness.
Despite its long history and growing interest in its therapeutic potential, the precise mechanisms by which psilocybin induces its effects, particularly its visual hallucinations, remain poorly understood. Traditional methods of studying hallucinations are limited because they occur unpredictably in clinical disorders. However, psychedelics like psilocybin reliably produce vivid visual experiences, making them valuable tools for exploring the neural basis of visual perception and imagery.
Previous research has indicated that psychedelics affect various brain regions involved in perception, but the detailed pathways and specific neural interactions have remained elusive. By using advanced imaging techniques and a well-controlled experimental design, the authors of the new study sought to elucidate the changes in brain connectivity that underlie the unique visual experiences induced by psilocybin.
“Visual effects are one of the main subjective phenomena induced by serotonergic psychedelics. Their underlying mechanisms remain a curiosity in psychedelic science and other research domains such as psychosis and dream states,” said study author Devon Stoliker, a postdoctoral researcher at the Turner Institute for Brain and Mental Health at Monash University.
“These visual phenomena also complement more profound experiences related to the dissolution of self and self-related boundaries, potentially having therapeutic relevance. For instance, visual experiences can be perceived as personally meaningful, and dissolved boundaries may facilitate insights or visions, potentially linked to visual brain areas. Although only a subsection of these ideas are explored in the article, they provide a compelling area for further research.”
The researchers conducted a double-blind, randomized, placebo-controlled, cross-over study, which is considered the gold standard for minimizing bias and ensuring robust results. This design means that neither the participants nor the researchers knew who received psilocybin or a placebo during each session, and each participant experienced both conditions at different times.
The study included 24 healthy adults aged 20 to 40, ensuring they had no history of psychiatric disorders. These participants underwent two sessions spaced at least two weeks apart. In one session, they received a dose of psilocybin (0.2 mg/kg of body weight), and in the other, a placebo. During each session, resting-state functional MRI (fMRI) scans were taken 70 minutes after administration, a time point corresponding to the peak effects of psilocybin. Participants were asked to keep their eyes closed during the scans to focus on the internal visual experiences.
Under the influence of psilocybin, brain regions involved in visual processing showed increased self-inhibition. This means these regions became less responsive to incoming sensory signals, reducing their sensitivity to external stimuli. Essentially, the brain’s internal activity took precedence over external sensory input.
The researchers also found strengthened connections from higher-order brain regions (like the inferior frontal gyrus) to lower-order visual areas (such as the early visual areas). This suggests that internal thoughts, memories, and associative processes had a greater influence on visual perception under psilocybin, leading to vivid and complex visual imagery.
There was a noticeable decrease in the brain’s response to external visual stimuli, aligning with previous preclinical findings. This reduction in sensory input allowed internally generated imagery to become more prominent, supporting the hypothesis that psychedelics enhance the brain’s reliance on top-down processes for visual perception.
The vividness and complexity of the visual imagery reported by participants were strongly correlated with specific patterns of brain connectivity. For example, connections from the inferior frontal gyrus to the fusiform gyrus and from the fusiform gyrus to the early visual areas were linked to the experiences of elementary and complex imagery, respectively.
“Psychedelics appear to inhibit the primacy of activity in visual areas, making these regions more susceptible to top-down influences from the brain,” Stoliker told PsyPost. “This aligns with the concept of psychedelics as ‘mind-manifesting’ substances, enhancing top-down processes. This notion also resonates with past research on alpha wave inhibition, suggesting that psychedelics may inhibit mechanisms that normally prevent us from seeing visual effects when our eyes are closed.”
Despite its robust design, the study has some caveats to consider. The small sample size of 20 participants (after exclusions) limits the generalizability of the findings. The study also used a moderate dose of psilocybin, so the effects of higher doses remain unexplored. Additionally, the study focused on a few specific brain regions and resting-state conditions; a broader exploration of brain areas and task-based research could provide a more comprehensive understanding.
“Psychedelic science is still developing, and methodological pipelines influence results,” Stoliker said. “Therefore, it’s wise to consider these findings as preliminary. Confidence builds when the majority of studies yield similar results.”
Nevertheless, the study’s results suggest that psychedelics could be used as tools to explore the brain’s intrinsic connectivity and its role in generating conscious experiences. Understanding how psilocybin affects brain connectivity could inform the development of new therapeutic approaches for conditions involving altered perceptions, such as schizophrenia or certain types of hallucinations.
“I aim to understand changes across the brain that inform our understanding of associative and sensory processes, and how they influence respective top-down and bottom-up mechanisms,” Stoliker explained. “Understanding these alterations can reveal how specific subjective effects are produced. While this research informs us about psychedelics, it also has the potential to reveal the mechanisms perception and nature of conscious experience.”
“I have an expansive exploration of the neural mechanisms and psychology of psychedelic ego dissolution published in Pharmacological Reviews, which may be of interest to readers: https://pharmrev.aspetjournals.org/content/74/4/876.”
The study, “Neural mechanisms of psychedelic visual imagery,” was authored by Devon Stoliker, Katrin H. Preller, Leonardo Novelli, Alan Anticevic, Gary F. Egan, Franz X. Vollenweider, and Adeel Razi.
