Reactivation of Hippocampal Ensemble Memories During Sleep

Abstract

Simultaneous recordings were made from large ensembles of hippocampal "place cells" in three rats during spatial behavioral tasks and in slow-wave sleep preceding and following these behaviors. Cells that fired together when the animal occupied particular locations in the environment exhibited an increased tendency to fire together during subsequent sleep, in comparison to sleep episodes preceding the behavioral tasks. Cells that were inactive during behavior, or that were active but had non-overlapping spatial firing, did not show this increase. This effect, which declined gradually during each post-behavior sleep session, may result from synaptic modification during waking experience. Information acquired during active behavior is thus re-expressed in hippocampal circuits during sleep, as postulated by some theories of memory consolidation.

Neuroscience and education: prime time to build the bridge

“…These findings close a causal loop that relates mnemonic gain to early-sleep neural synchronization. Animal studies have demonstrated that sleep triggers mnemonic reverberation at the level of action potentials 20 as well as calcium-dependent molecular events related to long-term memory storage 21,22 .…”

The Neural-Cognitive Basis of the Jamesian Stream of Thought

“…A third mode (sometimes called replay; Redish, 1999) can occur when there is no incoming sensory information (e.g., during sleep). In this case, the firing of the cells is determined by the intrinsic connections within the hippocampus, which will tend to cause the reinstantiation of firing sequences that correspond to routes that have been traveled in the past (Wilson & McNaughton, 1994;Skaggs & McNaughton, 1996). In both recall and replay, signals are sent through back projection pathways to the cortex, causing reinstantiation of the cortical firing pattern that originally triggered the now recovered hippocampal firing pattern.…”

Movement Coding at the Mesoscale in Posterior Parietal Cortex

“…In addition to sensorimotor functions, more recent work pointed toward a navigational role for PPC in monkeys, showing that neurons there encoded route segments in virtual reality houses, and that inactivating PPC caused the monkeys to lose their way (Sato et al, 2006). Recordings in rodents in the 80's and 90's also suggested a role for PPC in navigation (McNaughton et al, 1994). Here it was found that a substantial fraction of PPC cells (30-50%) encoded basic modes of movement, such as turning, running or combinations of movements while freely-behaving subjects traversed an 8-arm radial maze.…”

“…This is a surprising finding since the rodent PPC has rather weak connectivity with the hippocampal formation, where replay is most prevalent. Yet the post-task activity patterns in PPC exhibited several hallmarks of memory-related replay described originally in the hippocampus (Wilson and McNaughton, 1994), including the dependence on prior experience and the occurrence at compressed timescales. In some instances the replayed activity maintained the same sequential ordering across tetrodes as seen during the trajectory-running task, demonstrating that the internally generated activity patterns were organized across several hundred microns or more.…”