Oscillations and aperiodic activity: Evidence for dynamic changes in both during memory encoding

Electrical recordings of human brain activity via electroencephalography (EEG) show prominent, rhythmic voltage fluctuations. These periodic oscillations have been linked to nearly every cognitive and perceptual process, as well numerous disease states. Recent methodological and theoretical advances, however, have given rise to evidence for a functional role for non-oscillatory, aperiodic neural activity. Physiologically, this aperiodic activity has been linked to the relative contributions of neuronal excitatory and inhibitory signaling. Most importantly, however, traditional data analysis methods often conflate oscillations and aperiodic activity, masking the potentially separate roles these processes play in perception, cognition, and disease. Here we present a reanalysis of intracranial human EEG recordings from Fellner et al., 2019, using new methods for separately parameterizing oscillations and aperiodic activity in a time-resolved manner. We find that human memory encoding is not related to just oscillations or aperiodic activity, but rather that both processes are rapidly co-modulated during memory encoding. These results provide strong evidence for event-related dynamics of aperiodic and oscillatory activity in human memory, paving the way for future investigations into the unique functional roles of these two independent, but linked, processes in human cognition.