Memory trace replay: the shaping of memory consolidation by neuromodulation

Highlights

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  Memory trace replay results from lingering excitability and synaptic plasticity.

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  The balance of replay mechanisms may be determined by neuromodulation.

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  Acetylcholine release can shape the direction of replay in sharp wave ripples.

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  Dopamine release can dictate which cell assemblies are replayed.

Abstract

The consolidation of memories for places and events is thought to rely, at the network level, on the replay of spatially tuned neuronal firing patterns representing discrete places and spatial trajectories. This occurs in the hippocampal-entorhinal circuit during sharp wave ripple events (SWRs) that occur during sleep or rest. Here, we review theoretical models of lingering place cell excitability and behaviorally induced synaptic plasticity within cell assemblies to explain which sequences or places are replayed. We further provide new insights into how fluctuations in cholinergic tone during different behavioral states might shape the direction of replay and how dopaminergic release in response to novelty or reward can modulate which cell assemblies are replayed.