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A hippocampal 'sharp-wave sleep' state that is dissociable from cortical sleep
Graham Findlay1,2, Matias Lorenzo Cavelli1,3, Tom Bugnon1
1Department of Psychiatry, University of Wisconsin-Madison, Madison, WI, USA.
Nature Neuroscience
|December 11, 2025
Summary
Hippocampal sharp waves (SPWs) indicate sleep need, occurring during sleep and quiet wakefulness. These events suggest a partially disconnected, homeostatically regulated state in the hippocampus, termed "hippocampal sharp wave sleep".
Area of Science:
- Neuroscience
- Sleep Science
- Computational Neuroscience
Background:
- Cortical slow waves are established neural markers of sleep need and homeostatic regulation.
- Neural signatures of sleep need beyond the cortex remain largely unexplored.
Purpose of the Study:
- To investigate hippocampal activity patterns associated with sleep need.
- To determine if hippocampal events reflect homeostatic sleep regulation.
Main Methods:
- Chronic, continuous 48-hour Neuropixels recordings in male rats.
- Analysis of hippocampal sharp waves (SPWs), ripples, and dentate spikes (DSs) during sleep/wake cycles.
Main Results:
- Hippocampal SPWs, ripples, and DSs closely correlate with sleep need.
- These hippocampal events occur during behavioral sleep and quiet wakefulness.
- Expression of hippocampal events during wakefulness negatively correlates with their expression during subsequent sleep, indicating homeostatic function.
Conclusions:
- Hippocampal SPWs represent a partially disconnected, homeostatically regulated state in the hippocampus.
- This state is proposed as 'hippocampal sharp wave sleep'.
- The findings extend the understanding of sleep homeostasis beyond cortical mechanisms.
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