RCT · 2025
Ketamine and psilocybin change brain wave patterns in different ways, EEG re-analysis finds
- Original title
- Divergent effects of ketamine and psilocybin on EEG power spectral density in a mismatch negativity paradigm.
- Authors
- Soltanzadeh M, Wang Z, Allohverdi SG, et al.
- Journal
- Psychopharmacology, 2025
- Molecules
- Esketamine, Psilocybin
- Conditions
- Healthy volunteers
- Participants
- 35
- Evidence grade
- Low
- Source
- Read the original paper
The question
Do ketamine and psilocybin produce different signatures in brain electrical activity? The researchers looked at whether the two drugs shift distinct parts of the EEG frequency spectrum.
What they did
The team re-analyzed EEG (electroencephalography, a recording of electrical activity from the scalp) data collected earlier from healthy volunteers. Each person acted as their own control, receiving placebo on one occasion and the active drug on another: 19 people for S-ketamine and 16 for psilocybin. During recording, participants listened to a repeating tone sequence (an auditory “roving” task). The researchers separated the EEG signal into rhythmic (periodic) and non-rhythmic (aperiodic) components, the latter being used as an indirect marker of the balance between excitation and inhibition in brain circuits.
What they found
Ketamine significantly changed both the offset and the slope of the aperiodic part of the EEG spectrum, which the authors interpret as a shift in excitation-inhibition balance. Both drugs reduced alpha-band power in similar brain regions. Reduced beta-band activity was seen only with ketamine. The authors conclude that psilocybin’s effects were more confined to rhythmic (oscillatory) activity.
The fine print
This was a re-analysis of data collected for a different purpose, not a new trial, and the samples were small (19 and 16 people). Participants were healthy volunteers, so the findings say nothing directly about whether either drug helps people with depression or any other condition. EEG measures are indirect markers of brain function, not clinical outcomes, and blinding is difficult when drugs produce obvious subjective effects. This summary is based on the abstract only.
What it means
The study supports the idea that ketamine and psilocybin act on the brain through different routes, which may matter for understanding how each is being tested as a treatment. It does not tell us anything about how well either works for patients.
Evidence grade: Low. A secondary re-analysis of an older placebo-controlled crossover dataset, with small samples and brain-activity measures rather than clinical outcomes.
This summary is based on the study’s published abstract.