Representations of spatial location by aperiodic and alpha oscillatory activity in working memory

Poster Session B - Sunday, April 14, 2024, 8:00 – 10:00 am EDT, Sheraton Hall ABC

Andrew Bender¹ (abender@ucsd.edu), Bradley Voytek¹; ¹University of California, San Diego

Alpha oscillations in human visual cortical electrophysiology (EEG) coordinate population codes that retain the visual working memory (WM) content, with non-spatial feature storage bound to location irrespective of location’s task relevance. Alpha power tracks the specific spatial location of WM items, even when spatial position is task-irrelevant. However, these results rely on conventional spectral analyses, such as narrowband filtering within a predetermined frequency range, that conflate dynamic and task-related modifications in non-oscillatory, aperiodic activity as changes in oscillatory activity, even in the absence of actual oscillations. Through parameterization of both aperiodic and alpha oscillatory activity, we aim to disentangle the roles of aperiodic and alpha oscillatory activity in visual WM. We trained separate inverted encoding models on 112 total participants across 7 different, extant EEG datasets to assess the extent to which aperiodic and alpha oscillatory activity represent spatial location. We found that aperiodic-adjusted alpha power—more likely reflecting true oscillations—represents spatial location during the delay period across all seven tasks, confirming its role in maintaining the spatial location of the stimulus in WM. While aperiodic activity also represents spatial location, it does so primarily in the first 400 milliseconds following stimulus presentation, dropping significantly during the WM delay period. This suggests an automatic, stimulus-independent encoding of spatial location by aperiodic activity regardless of task-relevance. The differential time courses for spatial location representation by aperiodic and alpha oscillatory activity imply novel, unique contributions of aperiodic and alpha oscillatory activity to the encoding and maintenance of stimulus feature representations during visual WM.

Topic Area: EXECUTIVE PROCESSES: Working memory