Oscillatory correlates of intentional forgetting: The role of theta and alpha power in item-method directed forgetting.

Results from item-method directed forgetting suggest that individuals are able to intentionally forget processed information. Most research suggests that either selective rehearsal of to-be-remembered or inhibitory control of to-be-forgotten information is accountable for effects of intentional forgetting. Some research, however, hypothesized that the time to process information mediates the underlying mechanism. To test this hypothesis, the current study investigated associations between oscillatory power in theta (3 - 7.5 Hz) and alpha frequencies (8 - 13 Hz) and intentional forgetting in human participants and explored whether or not these mechanisms depended on processing time. Previously, theta power was shown to be associated with the creation of episodic memory traces and alpha power with inhibition. We therefore expected to find associations between these neural signatures and behavioral effects. Consistent with our hypotheses, we revealed increased theta power for to-be-remembered and increased alpha power for to-be-forgotten information and that the effects of activity in both frequency bands were influenced by the time individuals were given for processing the memory cue. These results suggest that not one but two mechanisms, rehearsal and inhibitory control, are accountable for item-method directed forgetting, both with different temporal profiles.Significance StatementWe investigated oscillatory activity in the EEG while participants completed an item-method directed forgetting task, in which the time given to process remember/forget instructions was varied. Our results revealed increased theta (3 - 7.5 Hz) and alpha (8 - 13 Hz) power for successfully forgotten information. Contrary to most research (Anderson & Hanslmayr, 2014), the reported pattern of results suggests a two-process account of directed forgetting. This account involves a faster rehearsal stage, associated with increased theta power, and a slower inhibitory control stage, associated with increased alpha power. Furthermore, we presented evidence that these processes were influenced by the time given to process remember/forget instructions, in line with behavioral studies (Fawcett & Taylor, 2008; Wetzel & Hunt, 1977).