Multiple Intrinsic Timescales Govern Distinct Brain States in Human Sleep

Human sleep exhibits multiple, recurrent temporal regularities, ranging from circadian rhythms to sleep stage cycles and neuronal oscillations during nonrapid eye movement sleep. Moreover, recent evidence revealed a functional role of aperiodic activity, which reliably discriminates different sleep stages. Aperiodic activity is commonly defined fi ned as the spectral slope chi of the 1/frequency (1/f chi) chi ) decay function of the electrophysiological power spectrum. However, several lines of inquiry now indicate that the aperiodic component of the power spectrum might be better characterized by a superposition of several decay processes with associated timescales. Here, we determined multiple timescales, which jointly shape aperiodic activity using human intracranial electroencephalography. Across three independent studies (47 participants, 23 female), our results reveal that aperiodic activity reliably dissociated sleep stage-dependent dynamics in a regionally specific fi c manner. A principled approach to parametrize aperiodic activity delineated several, spatially and state-specific fi c timescales. Lastly, we employed pharmacological modulation by means of propofol anesthesia to disentangle state-invariant timescales that may reflect fl ect physical properties of the underlying neural population from state-specific fi c timescales that likely constitute functional interactions. Collectively, these results establish the presence of multiple intrinsic time- scales that define fi ne the electrophysiological power spectrum during distinct brain states.