Submitted for presentation at 2005 meeting of the Society for Neuroscience

EEG correlates of subvocal rehearsal in working memory

G. Hwang-Grodzins1, J. Jacobs2, A. Geller2, J. Danker1, R. Sekuler1, M. J. Kahana2
1Volen Center for Complex Systems, Brandeis University, Waltham, MA, 02454 USA
2Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104

Evidence suggests that different processes are involved in verbal and nonverbal working memory, with verbal memory depending specifically on the subvocal rehearsal of items. We recorded EEG signals at 60 scalp electrodes while subjects performed a modified Sternberg task. In each trial, subjects judged whether a probe item was one of the three items in a just-presented list. Lists were composed of stimuli from one of five stimulus pools that either were verbally rehearsable (letters, words, meaningful pictures) or which resisted verbal rehearsal (plaidlike gratings, single dot locations). We found oscillatory correlates of verbal tasks in the theta (4-8Hz), alpha (9-12Hz), beta (14- 28Hz), and gamma (30-50Hz) frequency bands.

We report that power elicited by verbal stimuli was greater than that elicited by nonverbal stimuli. Enhanced verbal power (EVP) was most significant in theta in the left parieto-occipital area. EVP in alpha and beta was distributed in frontal and occipital areas, and EVP in gamma was localized centrally. Applying the additional constraint that oscillatory power between item presentations is greater than during item presentation, we found enhanced beta in the right frontal and occipital areas. We conclude that oscillations in all frequency bands increase during verbal processing and that beta is a direct correlate of subvocal rehearsal.

Keywords: Sternberg, EEG, subvocal rehearsal.