Does rehearsal matter? Left anterior temporal alpha and theta band changes correlate with the beneficial effects of rehearsal on working memory.

Rehearsal during working memory (WM) maintenance facilitates retrieval. Less is known about how rehearsal modulates WM delay activity. In the present study, 44 participants completed a Sternberg Task with either intact novel scenes or phase-scrambled scenes, which had similar color and spatial frequency but lacked semantic content. During each condition participants generated a descriptive label and covertly rehearsed or suppressed (repeated "the") during the delay. This was easy in the former but more difficult in the later condition where scenes lacked semantic content. Behavioral performance and EEG delay activity was analyzed as a function of maintenance strategy. Performance during WM revealed a benefit of rehearsal for phase-scrambled but not intact scenes. Examination of the absolute amplitude revealed three underlying sources of activity for rehearsal, including the left anterior temporal (TAL), left and midline parietal regions. Increases in alpha and theta activity in TAL were correlated with improvement in performance on WM with rehearsal only when labeling was not automatic (i.e. phase-scrambled scenes), which may reflect differences in labeling and rehearsal (i.e. semantic associations vs. shallow labels). We conclude that rehearsal only benefits memory for visual stimuli that lack semantic information, and that this is correlated with changes in alpha and theta rhythms.