Immediate-early gene expression at rest recapitulates recent experience.

Immediate-early genes (IEGs) are tightly coupled to cellular activity and play a critical role in regulating synaptic plasticity. While encoding spatial experience, hippocampal principal cells express IEGs in a behaviorally dependent and cell-specific manner. This expression can be detected through the use of cellular compartment analysis of temporal activity by fluorescence in situ hybridization to generate estimates of cellular activity that match direct neuronal recording under comparable conditions. During rest, IEG expression continues to occur in a small number of cells, and the role of this basal expression is unknown. Imaging IEGs expressed during exploration and adjacent rest periods reveals that "constitutive" IEG expression during rest is not random. Rather, consistent with proposed memory consolidation mechanisms, it recapitulates a subset of the pattern generated by recent experience.