Using the aperiodic slope across learning to predict sleep-based memory consolidation

Abstract

Homeostatic mechanisms adjust synaptic strengths to regulate neuronal activity across wake-sleep cycles. Although sleep supports memory consolidation, limited research has explored how sleep-induced homeostatic changes influence memory outcomes in humans. The EEG-derived aperiodic slope (1/f) could be a candidate measure of homeostatic memory processes through its reflection of neural excitation-inhibition balance. In this study, 27 participants learned object-word pairs, and completed an immediate recognition test before either a nap or equivalent wakeful period. Resting-state EEG was recorded, both before and after learning and the interval, to derive changes in aperiodic slope values. A delayed recognition test then assessed whether changes in the aperiodic slope (i.e., homeostatic activity) across learning and the interval predicted memory accuracy and N400 amplitude, an index of stimulus expectancy and recognition. Our study found evidence to suggest homeostatic renormalisation, for the nap condition only, indicated by a shift towards inhibition across sleep which was inversely related to the slope change across learning. Although the aperiodic slope change across the nap and wake intervals did not predict delayed memory accuracy, a shift towards inhibition during learning was beneficial for memory accuracy, only in the nap condition. Similarly, a shift towards inhibition across learning, followed by a shift towards excitation in the nap condition, predicted reduced N400 amplitudes. This suggests that homeostatic renormalisation across the nap influenced model updating and stimulus expectancy. This study provides evidence for a link between synaptic homeostatic processes and memory consolidation, emphasising the importance of encoding-related aperiodic activity in this relationship.