Electrophysiological effects of psilocybin co-administered with midazolam

The serotonergic psychedelic psilocybin induces glutamatergic neural plasticity and profoundly alters consciousness. Midazolam, a benzodiazepine and positive allosteric modulator of GABA _A receptors, blunts neural plasticity and induces conscious amnesia. In our recent open label pilot study, we co-administered psilocybin (25 mg) with intravenous midazolam, targeting midazolam doses that allowed maintained subjective experience (mild to moderate sedation) while blocking memory encoding. We reported preliminary results from high density scalp electroencephalography (EEG) recorded during dosing session. Here, we used linear mixed effects models to examine changes in EEG band power (delta, theta, alpha, beta, gamma), normalized Lempel Ziv complexity (LZCn), and spectral exponent (SE) as a function of time during the dosing session, and relate these changes to the subjective effects of the drugs measured with the Observer’s Assessment of Arousal and Sedation (OAA/S) and the Altered States of Consciousness (ASC) questionnaire. We found that SE, LZCn, and power in all frequency bands changed during drug administration, with an early (15-30 mins) increase in beta power and decrease in SE followed by increases in LZCn and SE and broadband decreases in power over the next 6 hours. OAA/S improved model fits for alpha power while ASC improved the model fits for SE and LZCn. These data are further evidence that the effects of psilocybin are maintained in the presence of midazolam, and that aspects of the subjective experience are captured by EEG measures.