Oscillatory correlates of intentional updating in episodic memory

The efficient use of our memory does not only require remembering encoded information, it also requires forgetting old out-of-date information. That such memory updating is part of our memory system is suggested by numerous behavioral studies. The physiological correlates of this process, however, still remain elusive. In this study we explore oscillatory correlates of memory updating as they occur in list-method directed forgetting. In this task, subjects are cued to forget a previously learned word list and to learn a new list of words instead. Such cuing typically leads to forgetting of the first list (List 1) and to memory enhancement of the second (List 2). Measuring EEGs during List-2 encoding, we identified two effects of the forget cue on oscillatory function: an increase in upper alpha power and a reduction in upper alpha phase coupling (11 to 13 Hz). Median-split analyses revealed that the two oscillatory effects were selectively related to the two behavioral effects. Whereas the increase in power was related to List-2 enhancement, the reduced phase coupling was related to List-1 forgetting. Our results point to separate neural origins of forgetting and enhancement and show that alpha oscillations play a critical role in intentional updating of episodic memory. (C) 2008 Elsevier Inc. All rights reserved.