New study provides insights into the neurophysiological basis of psilocybin-induced alterations in consciousness

New research published in iScience provides unique insights into how psilocybin alters brain activity during psychedelic experiences. The findings suggest that while the overall activity of the brain becomes more chaotic during the psychedelic state, the brain’s ability to maintain complex interactions in response to external stimulation is not affected.

Psilocybin is a naturally occurring psychedelic compound found in certain species of mushrooms, commonly known as “magic mushrooms.” The substance can induce profound changes in perception, cognition, and emotions, leading to altered states of consciousness. The scientists behind the new study were interested in better understanding the neurophysiological effects of psilocybin and their relationship to subjective experiences during altered states of consciousness.

“To this aim, we used a psychedelic substance and a brain-imaging technology: first, we used psilocybin, which acts as pharmaceutical tool to induce a well-defined altered state of consciousness. Second, a combination of transcranial magnetic stimulation and electroencephalography (EEG). This allows you to decode aspects of the underlying brain signature and visualize its current electrophysiological state,” said study author Andres Ort, a member of the Neurophenomenology of Consciousness Lab at the University of Zurich.

The researchers employed a method known as the Perturbational Complexity Index (PCI) to quantify the complexity of spatiotemporal activity patterns in the brain. They applied a perturbation to a specific area of the brain using transcranial magnetic stimulation and recorded the resulting electrical activity via EEG. The recorded brain signals were then analyzed to evaluate the complexity and integration of the neural responses.

“Psychedelics like psilocybin are ideal pharmaceutical tools to alter and study human consciousness,” Ort told PsyPost. “In analogy to the well established ultrasound technology, which transforms echo soundwaves into a grayscale to visualize tissues, transcranial magnetic stimulation sends an impulse to the cortex, which sends back a wave-like electromagnetic response. This response can be used to calculate the underlying complexity of information processing (as binary code in time and space) or to visualize the brain’s given state.”

Free daily newsletter

The study included 22 participants. Each participant took part in two EEG recording days that were randomly assigned and double-blind, meaning neither the participants nor the researchers knew whether they were receiving psilocybin or a placebo. There was a two-week gap between the two recording days.

Ort and his colleagues found that psilocybin did not significantly alter the PCI values, indicating that the complexity of the causal interactions within the brain remained stable during the altered states of consciousness induced by psilocybin. However, they did observe increased electroencephalographic signal diversity during restful states after psilocybin administration, suggesting a broader range of brain activity patterns.

In other words, the complexity of the brain’s activity during transcranial magnetic stimulation remained the same as in normal wakefulness, while the complexity of spontaneous brain activity increased during the psychedelic state.

“We disproved our initial hypothesis that psychedelic states (here with psilocybin) produce higher complexity,” Ort explained. “Unlike the observed reduction of complexity during dreamless sleep, anesthesia or minimally conscious states, the psychedelic state has the same quantitative complexity as in normal waking – even though the quality of the conscious experience has massively changed.”

This suggests that the brain’s ability to maintain complex interactions is unaffected during the psychedelic experience, but the ongoing activity becomes more chaotic.

The researchers also observed that the effects of psilocybin on brain activity were primarily seen in the frontal regions of the brain, which are associated with executive functions and behavioral control. These changes in the frontal cortex were linked to the phenomenological experiences reported by the participants, such as feelings of blissfulness and unity.

The PCI takes into account various factors, including the number of unique patterns observed in the brain activity, the duration and intensity of these patterns, and the spatial interactions between different brain regions. By quantifying the complexity and integration of brain activity, the PCI provides insights into the functional organization and dynamics of the brain.

“Interestingly, the combination of transcranial magnetic stimulation and EEG has the ability to probe and ‘diagnose’ brain states,” Ort said. “This could affect how we understand the code of psychoneurological conditions. Personally, this study shifted my understanding of how a brain works from a neurotransmitter-driven model to one where the brain is actually a vibrating and information integrating organ where frequency patterns are key.”

However, Ort noted that there is still much to learn about this novel neuroimaging method. “Today, we only understand marginally what TMS-evoked potentials (electrical responses in the brain), complexity measures and different frequency spectra emitted by the brain mean,” he told PsyPost. “Probing more brains in different states of consciousness will help understanding better this electromagnetic language.”

The study, “TMS-EEG and resting-state EEG applied to altered states of consciousness: oscillations, complexity, and phenomenology“, was authored by Andres Ort, John W. Smallridge, Simone Sarasso, Silvia Casarotto, Robin von Rotz, Andrea Casanova, Erich Seifritz, Katrin H. Preller, Giulio Tononi, and Franz X. Vollenweider.