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Nested sequences of hippocampal assemblies during behavior support subsequent sleep replay.
Céline Drieu1, Ralitsa Todorova1, Michaël Zugaro2
1Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, France.
Science (New York, N.Y.)
|November 10, 2018
Summary
During wakefulness, active movement is crucial for forming memories. Theta sequences, essential for memory encoding, are impaired by passive travel, hindering subsequent sleep consolidation.
Area of Science:
- Neuroscience
- Cognitive Science
- Memory Research
Background:
- Memory consolidation during sleep involves replay of neuronal activity.
- The role of network dynamics during initial memory storage (encoding) during wakefulness remains unclear.
- Both slow and fast (theta) timescale neuronal sequences are implicated in memory formation.
Purpose of the Study:
- To investigate the role of theta timescale sequences in the initial formation of memory traces during wakefulness.
- To determine if active versus passive experience affects neuronal sequence replay and subsequent memory consolidation.
- To test the hypothesis that nested neuronal sequences are critical for memory encoding.
Main Methods:
- Electrophysiological recordings of place cell activity in rats.
- Manipulating behavioral states (passive travel vs. active running on a treadmill) during memory encoding.
- Analyzing neuronal sequence activity on behavioral and theta timescales.
- Assessing subsequent sleep replay and memory consolidation.
Main Results:
- Passive travel on a model train degraded theta sequences in place cells, impairing sleep replay.
- Active running on a treadmill during transport preserved theta sequences and accurate trajectory replay during sleep.
- Behavioral timescale sequences were present in both conditions, but theta sequences were critical.
Conclusions:
- Theta timescale sequences, nested within slower sequences, are instrumental for the initial formation of memory traces.
- Active engagement during experience is necessary for generating theta sequences crucial for memory encoding.
- These findings support the role of specific neuronal dynamics during wakefulness in preparing memories for sleep-dependent consolidation.
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