The default mode network: where spontaneous thought meets memory consolidation.

The default mode network (DMN) is a distributed set of brain regions engaged during wakeful rest. Spontaneous thoughts - internally directed mental experiences that arise with relative freedom and few constraints on their content or transitions - are ubiquitous during wakeful rest. Spontaneous memory reactivation - neural events in which recently learned information is reinstated - also occurs at rest and has a fundamental role in long-term memory consolidation. Here, we synthesize emerging behavioral, theoretical, and neurophysiological evidence suggesting that DMN activity associated with spontaneous thought provides a neural context that promotes the propagation of reactivated information to aid consolidation. We highlight findings linking spontaneous thought to improved memory performance, discuss how specific DMN subsystems coordinate with the hippocampus during reactivation, and highlight recent studies that connect spontaneous thought content to memory reactivations. We conclude by outlining future directions to clarify the mechanistic role of spontaneous thought in memory consolidation mediated by the complex interplay between the DMN, hippocampus, and broader cortical networks.