More is less: increased processing of unwanted memories facilitates forgetting

Abstract

The intention to forget can produce long-lasting effects. This ability has been linked to suppression of both rehearsal and retrieval of unwanted memories - processes that are mediated by prefrontal cortex and hippocampus. Here, we describe an alternative account of deliberate forgetting in which the intention to forget is associated with increased engagement with the unwanted information. We used pattern classifiers to decode functional magnetic resonance imaging (fMRI) data from a task in which participants viewed a series of pictures and were instructed to remember or forget each one. Pictures followed by a forget instruction elicited higher levels of processing in ventral temporal cortex compared to those followed by a remember instruction. This boost in processing led to more forgetting, particularly for items that showed moderate (vs. weak or strong) activation. This result is consistent with the non-monotonic plasticity hypothesis, which predicts weakening and forgetting of memories that are moderately activated.