UC San Diego

Herein I examine neural variability and its relationship to healthy aging and short-term memory. This variability is apparent not only in the inconsistency with which neural populations respond to and process incoming stimuli, but also in how ongoing neural activity fluctuates over time even in the absence of such stimuli. First, I show using electroencephalography (EEG) that higher trial-by-trial variability in the visual cortical alpha phase response to task-relevant stimuli is associated both with healthy aging and with reduced behavioral performance in a visual short-term memory task. Next, and also in EEG, I use the 1/f-like or aperiodic slope of the electrophysiological power spectrum to characterize baseline fluctuations in neural activity, and I show that in healthy aging, higher alpha phase response variability is associated with the age-related flattening of the aperiodic slope of ongoing neural activity. Finally, I show using intracranial recordings that trial-by-trial shifts in the aperiodic slope of ongoing neural activity can help distinguish between episodes of successful versus unsuccessful memory encoding. I also show that shifts in ongoing neural activity index the number of items maintained and subsequently recalled from short-term memory. Altogether, these findings point to the continued need and utility of examining how neural variability, that in ongoing or in stimulus-evoked activity, can act as a neural signature both of age-related changes in behavior and of memory encoding and maintenance.