DMT alters cortical travelling waves

Introduction

N,N-Dimethyltryptamine (DMT) is a serotonergic psychedelic that produces a rapid, short-lived but intensely immersive visual and perceptual state. Earlier EEG and MEG studies of ayahuasca and of intravenously administered DMT have consistently reported broadband decreases in oscillatory power—particularly in the alpha band (8–12 Hz)—and increases in signal diversity; decreases in alpha power have correlated with the intensity of visual phenomenology. Separately, non-drug studies have described spatio-temporal patterns of cortical activity known as travelling waves: forward (occipital-to-frontal) waves predominate during visual perception, whereas backward (frontal-to-occipital) waves predominate during eyes-closed rest. These travelling waves have been linked to predictive-coding accounts in which direction of propagation relates to bottom-up prediction errors and top-down predictions respectively. Alamia and colleagues set out to test whether DMT alters the amount and direction of cortical travelling waves during eyes-closed resting conditions, and whether any such changes relate to the vivid visual imagery produced by the drug. The primary hypothesis was that DMT would disrupt the physiological balance between top-down and bottom-up information flow in favour of increased bottom-up signalling, manifesting as decreased backward waves and increased forward waves similar to those observed during actual visual stimulation. The study therefore aimed to quantify travelling-wave directionality and frequency under placebo versus intravenously administered DMT and to relate these measures to real-time and post-hoc subjective reports of intensity and visual imagery.