Bidirectional alpha collapse, not forward wave increase, under N,N-DMT: A reanalysis of cortical travelling waves

Abstract

Alamia et al. (2020) reported that N,N-dimethyltryptamine (DMT) significantly increases forward (bottom-up) cortical travelling waves, based on surrogate-normalized 2D FFT analysis. We reanalyze the same publicly available EEG dataset (N = 12) using the same method, supplemented by absolute power analysis. Absolute forward wave power decreases under DMT in all 12 subjects at alpha (8–13 Hz) and 11 of 12 at broadband (2–100 Hz); placebo produces no significant change in absolute power. Both forward and backward power collapse bidirectionally, with backward collapsing significantly more (2.3–5.1 percentage points, all p ≤ 0.002, 12/12 subjects at alpha). This differential persists in within-subject percentage changes, which inherently normalize each direction to its own baseline. The apparent normalized forward “increase” arises because the surrogate baseline inherits the spectral collapse and drops faster than the forward signal. Forward dB at the maximum measured effect was not significantly above zero (Bayes factor BF01 = 2.45, Jeffreys–Zellner–Siow prior r = √2/2; Rouder et al., 2009), providing anecdotal evidence for convergence to the surrogate null rather than emergence of new directional activity. At the maximum measured effect, absolute forward and backward alpha power were statistically indistinguishable (p = 0.27), consistent with both directions collapsing to a common floor. The electrophysiological signature of DMT is better described as bidirectional wave power collapse with loss of detectable directional structure at alpha frequencies than as directional reorganization.