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Trends Neurosci. 2013 Sep;36(9):497-503. doi: 10.1016/j.tins.2013.05.002. Epub 2013 Jun 12.

Hippocampal neurogenesis and forgetting.

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Program in Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada; Department of Psychology, University of Toronto, Toronto, Ontario M5S 3GM, Canada; Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Institute of Medical Science, University of Toronto, Toronto, Ontario M5S 1A8, Canada. Electronic address:


The hippocampus is thought to automatically encode all experience, yet the vast majority of our experiences are not remembered later. Although psychological theories have postulated the existence of decay processes for declarative memory, the corresponding neurobiological mechanisms are unknown. Here we develop the hypothesis that ongoing hippocampal neurogenesis represents a decay process that continually clears memories from the hippocampus. As newborn granule cells integrate into established hippocampal circuits, they form new input and output connections over the course of several weeks. Because successful memory retrieval relies on reinvoking patterns of activity that occurred at the time of encoding (pattern completion), neurogenesis-induced remodeling of hippocampal circuits incrementally reduces the likelihood that a given retrieval cue will reinvoke a previously stored pattern.

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