Time-resolved Neural and Experience Dynamics of Medium- and High-dose N,N-Dimethyltryptamine.

N,N-dimethyltryptamine (DMT) is a fast-acting psychedelic drug that induces a radical reorganization of conscious contents and brain dynamics. However, our understanding of how brain dynamics support psychedelic-induced conscious states remains unclear. We therefore present a repeated-measures dose-dependent study of the subjective and neural dynamics induced through DMT under naturalistic conditions. Nineteen participants received either a 20-mg or a 40-mg dose of freebase DMT across two sessions in a blinded, counterbalanced order. Electroencephalography data and time-resolved measures of subjective experience (Temporal Experience Tracing) were collected. Both doses of DMT induced rapid changes in experience dimensions, with the 40-mg dose inducing more extreme visual hallucinations and emotionally intense experiences. A variety of neural features were computed on the electroencephalography data, with oscillatory alpha power and permutation entropy most strongly associated with continuous subjective experience dimensions. Strikingly, Lempel-Ziv complexity, previously hailed as a robust correlate of subjective experiences within the psychedelic state, yielded the weakest associations. These findings suggest that the relationship between neural complexity and phenomenology in psychedelic states is less clear than originally hypothesized.