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A recent study published in Progress in Neuro-Psychopharmacology and Biological Psychiatry sheds light on how psilocybin alters human brain activity, shifting it from a resting state to a highly engaged pattern of processing. Scientists found that these measurable brain wave changes directly correspond to the intensity of a person’s psychedelic experience. The research also suggests that a person’s resting brain activity before taking the drug might predict how strongly they will respond, opening new possibilities for personalized therapies.
Psilocybin is the active chemical found in “magic mushrooms” that can cause profound changes in perception, mood, and thought. By interacting with specific serotonin receptors in the brain, the substance tends to promote neuroplasticity, which is the brain’s ability to form new connections. In recent years, scientists have explored its potential as a treatment for conditions like depression, addictive disorders, and post-traumatic stress disorder.
Early clinical trials suggest that even a single dose of psilocybin might help patients reconnect with their emotions and find meaning in daily experiences. Despite this promise, the exact ways psilocybin affects the brain’s rapid electrical activity remain partly unclear.
A research team from the University of Macau and the University of Zurich conducted this study to explore how psilocybin alters fast brain dynamics. They also wanted to see if measuring a person’s baseline brain activity could help explain why people have such different subjective experiences when taking the drug. Developing a better understanding of these mechanisms could help identify which patients are most likely to benefit from this intensive type of treatment.
“Many conventional antidepressants need to be taken daily, and some patients report emotional blunting, meaning they feel less engaged or less responsive to everyday experiences,” said study authors Cheng-Teng Ip and Sebastian Olbrich.
“In recent years, psilocybin has gained interest because early clinical studies suggest that even single administration may help patients reconnect with emotions and meaningful experiences. Yet despite this promise, we still know relatively little about what actually happens in the brain during these effects. In this study, we therefore used EEG to study how psilocybin changes fast brain dynamics and whether baseline brain activity might help explain why people differ in their subjective response.”
The scientists recruited 25 healthy individuals, consisting of 18 males and 7 females with an average age of about 24 years. The study used a double-blind, randomized, crossover design, meaning participants received both the active drug and a placebo on two separate days, spaced 14 days apart. Neither the participants nor the researchers knew which pill was being given on a specific measurement day.
The active dose was an oral capsule containing 10 to 20 milligrams of psilocybin, adjusted based on the participant’s body weight. The placebo was a visually identical capsule filled with inactive mannitol. During each session, the researchers recorded the brain’s electrical activity using an electroencephalogram, a non-invasive test that measures brain waves through small sensors attached to the scalp.
The scientists took 10-minute recordings before the participants took the capsule and again 60 minutes later, right before the drug’s effects were expected to peak. To measure the subjective psychedelic effects, participants completed a detailed survey called the Altered States of Consciousness Questionnaire. This survey evaluates different dimensions of the experience, such as feelings of unity, visual changes, auditory alterations, and anxiety.
When comparing the active drug to the placebo, the scientists observed clear shifts in brain wave patterns. Psilocybin reduced the power of slower brain rhythms, specifically theta and alpha waves. These slow waves are typically associated with relaxed, resting states and the regulation of basic human alertness.
At the same time, the drug increased the power of faster brain rhythms, known as beta and gamma waves. These fast brain waves are normally linked to high arousal, focused attention, and active information processing. This pattern suggests that psilocybin shifts the brain away from a normal idling state toward a highly dynamic and engaged state.
“Our results show that psilocybin produces clear changes in brain activity compared to placebo,” Ip and Olbrich told PsyPost. “In particular, we observed decreases in slower brain rhythms such as theta and alpha waves, which are typically linked to relaxed resting states and vigilance regulation, and increases in faster rhythms such as beta and gamma waves, which are often associated with heightened arousal and active information processing. This pattern suggests that psilocybin shifts the brain away from a typical resting-state pattern toward a more dynamically engaged brain state, possibly reflecting the vivid internally generated experiences that occur during the psychedelic state.”
The researchers also looked at how different parts of the brain communicate with each other, focusing heavily on the default mode network. This is a large-scale network of connected brain regions that typically activates when a person is daydreaming, reflecting on themselves, or letting their mind wander.
Under the influence of psilocybin, the scientists found increased communication and connectivity between the different regions of the default mode network. They also noted similar increases in connectivity within specific localized networks in the parietal lobe, an area near the back of the brain involved in processing sensory information.
When analyzing the survey responses, the researchers found that these changes in brain wave power and connectivity positively correlated with the participants’ subjective experiences. This means that individuals who showed the most intense shifts in their brain waves also reported the strongest psychedelic effects. For example, large clusters of fast brain wave activity correlated heavily with feelings of oceanic boundlessness, a term used to describe a sense of profound unity and positive mood.
“One striking finding was how closely the brain activity changes tracked the subjective psychedelic experience,” the researchers said. “The stronger the changes we observed in specific brain rhythms and network interactions, the more intense participants reported their experiences to be.”
The scientists also tested whether a participant’s brain activity before taking the drug could predict their later experience. They found that specific baseline brain wave patterns, particularly fast wave activity in the frontal and emotional centers of the brain, predicted the intensity of the subjective psychedelic experience. Individuals with higher baseline activity in these regions tended to report more profound psychological alterations after taking psilocybin.
“We were also intrigued to see that certain baseline EEG features were associated with how strongly individuals later responded to psilocybin,” Ip and Olbrich explained. “This suggests that the brain’s initial state before taking the drug may play an important role in shaping the psychedelic experience.”
While these findings provide evidence of how psilocybin alters brain function, there are a few limitations to consider. The study involved a relatively small sample of just 25 healthy participants. Two of the placebo recordings also had to be excluded due to technical issues, which slightly reduced the amount of usable data. This small sample size can restrict how broadly the findings can be applied to the general population.
“Although the study was conducted in healthy volunteers, identifying these neural patterns helps build a foundation for future work in patient populations and may eventually contribute to developing biomarkers that help guide psychedelic-assisted treatments,” Olbrich and Ip said.
In the future, the scientists plan to extend this line of research to clinical populations, including patients with major depressive disorder. They hope to determine whether brain wave patterns or other physiological signals, like heart rate variability, can serve as reliable biological markers.
“One of our longer-term goals is to better understand the mechanism that underlies psilocybin’s therapeutic effects,” the researchers told PsyPost. “There is an ongoing discussion about how much clinical improvement arises from psilocybin’s pharmacological effects and how much it depends on the accompanying psychotherapy and integration sessions.”
“At the same time, psychedelic treatments are relatively resource-intensive, typically requiring several hours of monitored treatment sessions alongside multiple preparation and integration meetings. As such, developing biological markers that help predict treatment response could therefore become very important for guiding patient selection and improving the efficiency and scalability of these therapies in the future.”
“This study examined how psilocybin alters brain activity in healthy participants during the psychedelic state,” Ip and Olbrich continued. “Our group is now extending this work to clinical populations to clarify how central and peripheral physiological signals relate to treatment outcomes.”
“In an upcoming study in patients with major depressive disorder, we are also examining how psilocybin affects heart rate variability and whether autonomic markers might help predict therapeutic response. In that cohort, we observed a comparable pattern of measurable physiological shifts, suggesting that psilocybin may modulate not only large-scale brain dynamics but also autonomic regulation.”
The study, “Psilocybin-induced alterations in EEG power, connectivity and network dynamics in healthy subjects: Correlations with subjective experience and implications for therapeutic applications,” was authored by Cheng-Teng Ip, Sebastian Olbrich, Mateo de Bardeci, Anna Monn, Andres Ort, John W. Smallridge, and Franz Vollenweider.
