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Persistence of neuronal representations through time and damage in the hippocampus

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Science  23 Aug 2019:
Vol. 365, Issue 6455, pp. 821-825
DOI: 10.1126/science.aav9199

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Robust memories through neuron networks

How does the brain store information over a long period of time? Gonzalez et al. chronically implanted custom-built high-sensitivity microendoscopes and performed long-term imaging of neuronal activity in freely moving mutant mice. The majority of neurons were active on most days, but their firing rate changed across sessions and tasks. Although the responses of individual neurons changed, the responses of groups of neurons with synchronous activity were very stable across days and weeks. In addition, the network activity in hippocampal area CA1 recovered after an extended period without performing the task or even after abnormal activity induced by local lesions. These findings indicate the presence of attractor-like ensemble dynamics as a mechanism by which the representations of an environment are encoded in the brain.

Science, this issue p. 821

Abstract

How do neurons encode long-term memories? Bilateral imaging of neuronal activity in the mouse hippocampus reveals that, from one day to the next, ~40% of neurons change their responsiveness to cues, but thereafter only 1% of cells change per day. Despite these changes, neuronal responses are resilient to a lack of exposure to a previously completed task or to hippocampus lesions. Unlike individual neurons, the responses of which change after a few days, groups of neurons with inter- and intrahemispheric synchronous activity show stable responses for several weeks. The likelihood that a neuron maintains its responsiveness across days is proportional to the number of neurons with which its activity is synchronous. Information stored in individual neurons is relatively labile, but it can be reliably stored in networks of synchronously active neurons.

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