Tracking selective rehearsal and active inhibition of memory traces in directed forgetting

Abstract

Selectively remembering or forgetting newly encountered information is essential for goal-directed behavior. It is still an open question, however, whether intentional forgetting is an active process based on the inhibition of unwanted memory traces or whether it occurs passively through reduced recruitment of selective rehearsal [1,2]. Here we show that intentional control of memory encoding relies on both, enhanced active inhibition and decreased selective rehearsal, and that these two processes can be separated in time and space. We applied representational similarity analysis (RSA [3]) and timefrequency analysis to EEG data during an item-method directed forgetting experiment [4]. We identified neural signatures of both the intentional suppression and the voluntary upregulation of item-specific representations. Successful active forgetting was associated with a downregulation of item-specific representations in an early time window, 500ms after the instruction. This process was initiated by an increase in oscillatory alpha (8-13 Hz) power, a well-established signature of neural inhibition [5,6], in occipital brain areas. During a later time window, 1500ms after the cue, intentional forgetting was associated with reduced employment of active rehearsal processes, as reflected by an attenuated upregulation of item-specific representations as compared to intentionally encoded items. Our data show that active inhibition and selective rehearsal are two separate mechanisms whose consecutive employment allows for a voluntary control of memory formation.