Eighteen volunteers (15 men, 3 women, mean age 25.7, reporting at least 5 prior uses of psychedelic drugs, healthy and with no diagnosis of major mental disorders received two doses of ayahuasca (freeze-dried, encapsulated) measured at 0.6 and 0.85 mg/kg DMT. (All participants received an initial placebo in a single-blind condition to familiarize them with the setting and procedures.) Data from the same sample are reported on in a previously published paper (see above). Quantitative electroencephalography (Q-EEG) was obtained with a 19-electrode system, with EEG recorded at intervals over an 8 hour period after drug administration. Vigilance recordings lasting 3 minutes were made at 15, 30, 45, 60, 90, 120, 180, 210, 240, 360 and 480 minutes after drug administration. Absolute and relative power were measured for delta, theta, alpha1, alpha2, four distinct beta bands, combined frequencies, and dominant frequency. As previously reported, subjective effects were reported via Spanish-language version of the Hallucinogen Rating Scale (HRS), containing 6 sub-scales; affect, cognition, intensity, perception, somasthenia, and volition). All changes in EEG were dose-dependent. 0.6 mg/kg DMT produced changes at isolated electrodes from 45 to 180 min (2.5 h) post-drug, and 0.85 mg/kg DMT produced changes at extensive locations. Changes in EEG seen after 0.85 mg/kg DMT reached significance at 60 min (1 h), peaking between 90 and 120 min (1.5 to 2 h) and gradually declining until effects disappeared 6 to 8 hours post-drug. Absolute delta-theta power was decreased after both 0.6 and 0.85 mg/kg DMT, with a greater decrease appearing in the theta band. Peak decline was seen between 90 and 120 minutes. Relative decline in theta band activity was also seen after both doses of ayahuasca, with peak decline seen at 120 minutes post-drug. Absolute alpha power declined after 0.6 and 0.85 mg/kg DMT, declining most prominently in left temporal and central-parietal-occipital areas after 0.85 mg/kg DMT. Decrease in Alpha2 was greater than that for Alpha1. Yet relative alpha activity increased 120 min after drug administration, with 0.6 mg/kg DMT producing a greater increase than 0.85 mg/kg DMT. There were significant shifts in central values for Alpha activity. Both the low and the high dose of ayahuasca decreased absolute beta activity, with a peak at 90 minutes post-drug. Beta1 was the most strongly affected. Yet there were relative increases in beta activity after ayahuasca seen between 45 and 90 min after drug administration, with increases more prominent after 0.85 mg/kg DMT. Relative Beta-3 and Beta-4 activity was significantly increased after both doses of ayahuasca. The beta band showed a centroid shift toward higher values after 0.6 and 0.85 mg/kg DMT ayahuasca, with shift strongest 90 minutes after drug administration. 0.6 mg/kg DMT ayahuasca was only significantly different from placebo at 45 and 60 minutes after drug administration when examined via non-parametric multilevel EEG analysis. However, 0.85 mg/kg DMT ayahuasca was significantly different from placebo from 45 to 120 minutes post-drug. Changes were seen as early as 15 minutes after drug administration. Subjective effects are only briefly described in this report; a more detailed description can be found in the preceding paper. The changes seemed to parallel the course of subjective effects, at least in onset, duration and decline.

This is the first report of EEG findings in a placebo-controlled study of ayahuasca. On examining Q-EEG findings, the authors indicate that ayahuasca produces changes in EEG similar to changes reported after psychostimulants, such as amphetamine and methylphenidate, and after serotonin releasers such as fenfluramine. Changes are also somewhat similar to changes seen after MDMA (Frei et al. 2001). These similarities may arise from increased brain monoamine content, produced by the MAO inhibiting actions of ayahuasca, and they may also arise because activating the serotonin 5HT2A receptor produces dopamine release. The authors note that Q-EEG findings of decreased theta activity are opposite those produced by the 5HT1A partial agonist buspirone, suggesting either that any 5HT1A activity possessed by ayahuasca does not influence its EEG profile or that there are differences between partial and full agonists at this receptor. Along with the previous paper, this report indicates that ayahuasca can be safely administered to humans in a controlled setting, without any interventions. While the relationship between Q-EEG measures and subjective effects remains unclear, further research might allow for unearthing relationships between measures of brain activity and assessment of subjective effects or behavior seen after psychedelic drugs.