Psilocybin alters brain activity related to sensory and cognitive processing in a time-dependent manner

Psilocybin is a classic psychedelic and a novel treatment for mood disorders. Psilocybin induces dose-dependent transient (4-6 hours) usually pleasant changes in perception, cognition, and emotion by non-selectively agonizing the 5-HT2A receptors and negatively regulating serotonin reuptake, and long-term positive antidepressant effect on mood and well-being. Long-term effects are ascribed to the psychological quality of the acute experience, increase in synaptodensity and temporary (1-week) down-regulation of 5-HT2A receptors. Electroencephalography, a non-invasive neuroimaging tool, can track the acute effects of psilocybin; these include the suppression of alpha activity, decreased global connectivity, and increased brain entropy (i.e. brain signal diversity) in eyes-closed resting-state. However, few studies investigated how these modalities are affected together through the psychedelic experience. The current research aimed to evaluate the psilocybin intoxication temporal EEG profile. 20 healthy individuals (10 women) underwent oral administration of psilocybin (0.26 mg/kg ) as part of a placebo-controlled cross-over study, resting-state 5-minute eyes closed EEG was obtained at baseline and 1, 1.5, 3, 6, and 24 hours after psilocybin administration. Absolute power, relative power spectral density (PSD), power envelope global functional connectivity (GFC), Lempel-Ziv complexity (LZ), and a Complexity via State-Space Entropy Rate (CSER) were obtained together with measures of subjective intensity of experience. Absolute power decreased in alpha and beta band, but increased in delta and gamma frequencies. 24h later was observed a broadband decrease. The PSD showed a decrease in alpha occipitally between 1 and 3 hours and a decrease in beta frontally at 3 hours, but power spectra distribution stayed the same 24h later. The GFC showed decrease acutely at 1, 1.5, and 3 hours in the alpha band. LZ and showed an increase at 1 and 1.5 hours. Decomposition of CSER into functional bands shows a decrease in alpha band but increase over higher frequencies. Further, complexity over a source space showed opposing changes in the Default Mode Network (DMN) and visual network between conditions, suggesting a relationship between signal complexity, stimulus integration, and perception of self. In an exploratory attempt, we found that a change in gamma GFC in DMN correlates with oceanic boundlessness. Psychological effects of psilocybin may be wrapped in personal interpretations and history unrelated to underlying neurobiological changes, but changes to perception of self may be bound to perceived loss of boundary based on whole brain synchrony with the DMN in higher frequency bands.