Individual differences in working memory capacity are reflected in different ERP and EEG patterns to task difficulty.

This study examined whether there are neural markers of individual differences in working memory (WM) capacity and whether these differences are only manifest when performing a demanding WM task or at all levels of difficulty. Each subject's WM capacity was estimated using a modified digit span task prior to participation in an N-back task that varied difficulty from 1- to 4-back. While performing the N-back task, subjects wore scalp electrodes that allowed measurement of both event-related potentials (ERP) and event-related synchronization and desynchronization (ERS/ERD). Those subjects classified as low WM were more affected by the higher cognitive demands (many more errors in the 4-back task and generally slower responses) than those classified as high WM. These behavioral differences between the two groups were also apparent in the neural markers. Specifically, low WM subjects, when compared with high WM subjects, produced smaller P300 amplitudes and theta ERS, as well as greater alpha ERD at the most difficult level. Importantly, the observed differences in electrophysiological responses between the two groups were also observed at the lowest difficulty level, not just when the task challenged WM capacity. In addition, P300 amplitudes and alpha ERD responses were found to correlate with individual WM capacities independent of the task difficulty. These results suggest that there are qualitative neural differences among individuals with different WM capacities when approaching cognitive operations. Individuals with high WM capacities may make more efficient use of neural resources to keep their attention focused on the task-relevant information when performing cognitive tasks.