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The ups and downs of hippocampal modulation: mnemonic consequences of memory control.
Eighteenth Annual Meeting of the Cognitive Neuroscience Society, G38
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People often try to control which memories enter awareness, and these efforts have been shown to have lasting consequences for the later accessibility of suppressed memories. In the Think/No-Think (TNT) procedure used to study such control, intentionally suppressing retrieval leads to a reduction, rather than an augmentation, in hippocampal activity. We hypothesized that this modulation would alter one’s ability to encode and consolidate novel information presented between TNT trials. Specifically, attempts to suppress retrieval prior to an incidental-encoding task should disrupt encoding, whereas suppressing retrieval after incidental encoding should truncate ongoing consolidation. In the current series of studies, we employed the novel Hippocampal Modulation (H.M.) paradigm, in which participants confronted novel stimuli presented between TNT trials. Both source recognition memory and cued-recall for items presented around suppression trials were significantly impaired. Thus, engaging cognitive control to suppress retrieval can be adaptive for preventing unwanted memories from entering awareness, but detrimental to the encoding or retention of experiences in the temporal surround. The H.M. paradigm offers a means of selectively and temporarily modulating the hippocampus in healthy human participants, thereby providing a non-invasive, focused method to study the functions of the hippocampus. The current results indicate that, as a result of suppressing unwanted thoughts, one is disadvantaged for learning new mnemonic connections. Individuals who chronically suppress memories could fall victim to extensive gaps in memory resulting from their coping strategy. Adopting alternative strategies to deal with unwanted thoughts that do not induce a hippocampal deactivation may be preferable in these circumstances.