PerspectiveNeuroscience

Spikes in the sleeping brain

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Science  18 Oct 2019:
Vol. 366, Issue 6463, pp. 306-307
DOI: 10.1126/science.aaz4534

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Summary

Memories of recent experiences are transferred and fixed in long-term storage in the neocortex during sleep. A key aspect of this process is the occurrence of ripples, which are high-frequency oscillations in neuronal activity in the hippocampus (1, 2). Ensembles of hippocampal neurons that have been activated during an experience emit synchronized neuronal activity (spikes) during ripples in subsequent sleep (3). These “replayed” memories propagate to the neocortex during slow-wave states (4), which are characterized by alternating “bright” states with active neurons and “dark” states, called delta waves, without active neurons (5). Researchers reasoned that hippocampal-cortical dialogue occurs during the bright states and that delta waves represent intermittent neocortical “sleep” to recover from synaptic fatigue (6) or increased potassium conductance (7) and have no active function. On page 377 of this issue, Todorova and Zugaro (8) challenge this view, demonstrating that a small number of neurons are reactivated during delta waves.

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