Preferential reactivation of motivationally relevant information in the ventral striatum.

Spontaneous "off-line" reactivation of neuronal activity patterns may contribute to the consolidation of memory traces. The ventral striatum exhibits reactivation and has been implicated in the processing of motivational information. It is unknown, however, whether reactivating neuronal ensembles specifically recapitulate information relating to rewards that were encountered during wakefulness. We demonstrate a prolonged reactivation in rat ventral striatum during quiet wakefulness and slow-wave but not rapid eye movement sleep. Reactivation of reward-related information processed in this structure was particularly prominent, and this was primarily attributable to spike trains temporally linked to reward sites. It was accounted for by small, strongly correlated subgroups in recorded cell assemblies and can thus be characterized as a sparse phenomenon. Our results indicate that reactivated memory traces may not only comprise feature- and context-specific information but also contain a value component.