EEG Correlates of Subjective Experience During and Following Psychedelic in Humans: A Scoping Review

Abstract

This scoping review will systematically identify, characterize, and map the human literature examining relationships between electroencephalography (EEG)-derived neurophysiological measures and subjective experiences associated with psychedelic states. Psychedelic compounds produce profound alterations in perception, cognition, affect, self-related processing, and the experience of time and space. EEG provides high temporal resolution for investigating the neural dynamics accompanying these altered states, and an increasing number of studies have examined whether specific electrophysiological changes are associated with the intensity or phenomenological character of psychedelic experiences. The primary purpose of this review is to determine which EEG-derived measures have been associated with specific dimensions of subjective psychedelic experience and to characterize the direction, consistency, and strength of these relationships. The review will consider a broad range of EEG measures, including spectral power and oscillatory activity, aperiodic activity, signal complexity and diversity, entropy, connectivity and synchrony, microstates, cross-frequency coupling, and other quantitative measures of neural dynamics. The review will include human studies involving eligible psychedelic compounds and will consider healthy and clinical populations, experimental and naturalistic settings, and resting-state and task-based EEG recordings. Studies will be eligible for the primary synthesis when they report both a quantitative EEG measure and a quantitative measure of subjective experience, phenomenology, or a subsequent psychological or therapeutic outcome, and examine a statistical relationship between these measures. Findings will be organized according to phenomenological domains, including overall subjective intensity, perceptual alterations, self-related experiences such as ego dissolution, mystical or transcendent experiences, cognitive and affective effects, alterations in time or space, and post-acute psychological or therapeutic outcomes. EEG findings will also be classified according to the type of neurophysiological measure used. This approach will allow relationships between specific EEG features and specific aspects of psychedelic experience to be distinguished from general EEG changes associated with psychedelic administration. The review will use a scoping-review methodology to accommodate substantial heterogeneity in psychedelic compounds, doses, EEG acquisition and analysis methods, timing of measurements, subjective-experience instruments, and study populations. Results will be synthesized using descriptive and structured narrative approaches, with quantitative synthesis considered where sufficient methodological and conceptual homogeneity exists. Expected outcomes include an evidence map of EEG measures and their relationships with distinct dimensions of psychedelic experience, identification of EEG–experience associations that appear consistent across psychedelic compounds, characterization of findings that may be compound- or context-specific, and identification of important gaps and methodological limitations in the existing literature. The review will also identify priorities for future studies designed to clarify the neurophysiological basis of specific psychedelic experiences. The review will not assume that any EEG measure constitutes a validated biomarker of a particular subjective experience; rather, it will evaluate the current evidence for such relationships and characterize the strength and limitations of the available evidence.

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