Replay, the default mode network and the cascaded memory systems model

Spontaneous replay of past experiences and coherent activation of the default mode network (DMN) are both prominent during rest, and the authors propose they are deeply linked. Their cascaded memory systems model hypothesizes that the DMN serves as a backbone for propagating replay, mediating interactions between the hippocampus and neocortex to consolidate new memories. The DMN may also independently ignite replay cascades that reactivate older memories or high-level semantic representations. Transient cortical activations that induce long-range correlations across the neocortex are suggested as a key mechanism supporting a hierarchy of representations from simple percepts to episodes.

Study at a glance

Abstract

The spontaneous replay of patterns of activity related to past experiences and memories is a striking feature of brain activity, as is the coherent activation of sets of brain areas — particularly those comprising the default mode network (DMN) — during rest. We propose that these two phenomena are strongly intertwined and that their potential functions overlap. In the ‘cascaded memory systems model’ that we outline here, we hypothesize that the DMN forms the backbone for the propagation of replay, mediating interactions between the hippocampus and the neocortex that enable the consolidation of new memories. The DMN may also independently ignite replay cascades, which support reactivation of older memories or high-level semantic representations. We suggest that transient cortical activations, inducing long-range correlations across the neocortex, are a key mechanism supporting a hierarchy of representations that progresses from simple percepts to semantic representations of causes and, finally, to whole episodes. Battaglia and colleagues discuss evidence for functional interactions between memory replay and default mode network (DMN) activity and propose an updated model of memory consolidation and retrieval in which the DMN acts as a hub for cascaded replay across the brain.