Sleep Promotes the Neural Reorganization of Remote Emotional Memory

TLDR

Sleep consolidates memories by reorganizing them into stable representations, and emotional memories are generally better retained than neutral ones over long delays. The study examined how sleep during the night after encoding affects the neural correlates of recollection of emotional memories six months later. Participants incidentally encoded emotional and neutral pictures, then either slept or were sleep‑deprived the first post‑encoding night, and later underwent fMRI at 3 days and 6 months while sleeping normally between sessions. At six months, recollection was associated with greater activation in the vMPFC, precuneus, extended amygdala, and occipital cortex and stronger connectivity among these regions in the sleep group versus the sleep‑deprived group, indicating that sleep during the first night drives long‑term consolidation of emotional memory.

Abstract

Sleep promotes memory consolidation, a process by which fresh and labile memories are reorganized into stable memories. Emotional memories are usually better remembered than neutral ones, even at long retention delays. In this study, we assessed the influence of sleep during the night after encoding onto the neural correlates of recollection of emotional memories 6 months later. After incidental encoding of emotional and neutral pictures, one-half of the subjects were allowed to sleep, whereas the others were totally sleep deprived, on the first postencoding night. During subsequent retest, functional magnetic resonance imaging sessions taking place 3 d and 6 months later, subjects made recognition memory judgments about the previously studied and new pictures. Between these retest sessions, all participants slept as usual at home. At 6 month retest, recollection was associated with significantly larger responses in subjects allowed to sleep than in sleep-deprived subjects, in the ventral medial prefrontal cortex (vMPFC) and the precuneus, two areas involved in memory retrieval, as well as in the extended amygdala and the occipital cortex, two regions the response of which was modulated by emotion at encoding. Moreover, the functional connectivity was enhanced between the vMPFC and the precuneus, as well as between the extended amygdala, the vMPFC, and the occipital cortex in the sleep group relative to the sleep-deprived group. These results suggest that sleep during the first postencoding night profoundly influences the long-term systems-level consolidation of emotional memory and modifies the functional segregation and integration associated with recollection in the long term.