Long-duration hippocampal sharp wave ripples improve memory

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Science  14 Jun 2019:
Vol. 364, Issue 6445, pp. 1082-1086
DOI: 10.1126/science.aax0758

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Longer ripples make better memories

Sharp wave ripples in the hippocampus are thought to play a role in memory formation and action planning. Fernández-Ruiz et al. used multisite electrophysiological recordings combined with optogenetic activation of hippocampal pyramidal neurons in rats performing learning tasks. Learning and correct recall in spatial memory tasks were associated with extended sharp wave ripples. Artificially prolonging these ripples improved working memory performance, whereas aborting the late part of ripples decreased performance.

Science, this issue p. 1082


Hippocampal sharp wave ripples (SPW-Rs) have been hypothesized as a mechanism for memory consolidation and action planning. The duration of ripples shows a skewed distribution with a minority of long-duration events. We discovered that long-duration ripples are increased in situations demanding memory in rats. Prolongation of spontaneously occurring ripples by optogenetic stimulation, but not randomly induced ripples, increased memory during maze learning. The neuronal content of randomly induced ripples was similar to short-duration spontaneous ripples and contained little spatial information. The spike content of the optogenetically prolonged ripples was biased by the ongoing, naturally initiated neuronal sequences. Prolonged ripples recruited new neurons that represented either arm of the maze. Long-duration hippocampal SPW-Rs replaying large parts of planned routes are critical for memory.

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