Ayahuasca changed brain waves and experiences in 50 healthy volunteers

The question

What happens to subjective experience, spontaneous thinking and brain-wave activity after drinking ayahuasca, and can brain activity measured beforehand predict the kind of experience a person has?

What they did

Fifty healthy volunteers were randomly assigned, in a double-blind design, to receive either ayahuasca (1 mL per kg of body weight) or a placebo. Researchers used questionnaires to measure the psychedelic experience (the Hallucinogen Rating Scale and the Mystical Experience Questionnaire) and the content of resting thought, or “mind-wandering” (the Amsterdam Resting-State Questionnaire). Electroencephalography (EEG), which records electrical rhythms from the scalp, was recorded before the drink and again 2 hours and 4 hours afterwards.

What they found

Compared with placebo, ayahuasca produced changes in perception, thinking and emotion, more mystical-type experiences, and more visual, disjointed and content-rich mind-wandering. EEG rhythms also shifted: alpha waves decreased across the whole scalp, while delta waves increased at the front-middle of the head and theta and beta waves increased at the right back of the head. During the ayahuasca session, lower theta activity went along with stronger mystical experiences, and higher alpha went along with fewer reports of “thoughts about nothing”. Baseline EEG before dosing also tracked later experience: lower theta was linked to stronger bodily awareness and “rush” ratings, and lower beta was linked to higher ratings of feeling happy.

The fine print

This was a small study in healthy volunteers, so it says nothing about treating any mental health condition. The brain-wave findings are correlations, not proof that one causes the other, and many measures were analysed, which raises the chance of some links appearing by chance. Ayahuasca’s strong effects make true blinding difficult, follow-up was only hours long, and this summary is based on the abstract alone.

What it means

Ayahuasca reliably altered perception, emotion and spontaneous thought while shifting measurable brain rhythms, and brain activity recorded before dosing showed some relationship to the type of experience people later had.

Evidence grade: Moderate. Randomized, double-blind, placebo-controlled trial, but small, in healthy volunteers, and measuring brain-wave and questionnaire outcomes rather than clinical benefit.

This summary is based on the study’s published abstract.