Multifaceted pattern of neural efficiency in working memory capacity

The objective of the present study was to investigate whether neural efficiency can be observed in visual working memory performance. Thirty low- and thirty high-performers were selected from a larger cohort of students based on performance on a visual WM task. Electroencephalogram (EEG) data during performance on this task was analyzed with event-related desynchronization/synchronization (ERD/ERS) and event-related coherence (ErCoh) in individually determined theta, alpha, and gamma frequency bands. The results demonstrated that high-performers in comparison to low-performers showed significantly different brain oscillatory responses in all three cognitive processes identified in the WM task - encoding, maintenance and retrieval. High-performers displayed: (1) Increased alpha ERD during encoding and increased gamma ERD during encoding and maintenance, which did not depend on set size, as well as (2) increased theta band ErCoh in fronto-parietal networks during maintenance and retrieval. To some extent, neural efficiency was observed in the gamma frequency band (ERD) and in theta coherence (ErCoh). The results tentatively lend support to the continuous single resource model assuming that working memory capacity is a flexible resource that can be spread among all elements in the sensory input as opposed to the model of discrete slots.