Memory and Learning
Matt Wilson, RIKEN-MIT Neuroscience Research Center
One of our fundamental working hypotheses is that experience leads to changes in the hippocampus that preserve both the content and the temporal linkage of events that constitute episodic memory. Long-term neocortical memory may be formed through interactions with memory structures such as the hippocampus, and memory reactivation during sleep may play a critical role in this consolidation process. By introducing arrays of microelectrodes into hippocampal and neocortical areas of freely behaving rodents we have been able to examine the coordinated activity of ensembles of large numbers of individual cells that may reflect this memory processing.
Previous work found that temporal sequences of neural ensemble activity generated during awake experience spanning several minutes were reproduced during REM episodes at equivalent timescales (Louie and Wilson, 2001). We further identified evidence of memory replay of brief episodes of experience during non-REM sleep that occurred at an accelerated rate with several seconds of recent experience being replayed in brief bursts, a fraction of a second in duration (Lee and Wilson, 2002).
More recent work has identified similar temporal replay of recent experience that occurs during periods of quiet wakefulness in the context of ongoing behavioral tasks as well as the reactivation of memory sequences in the neocortex during sleep. These novel reactivation events may reflect the processing of sequential experience during active learning and memory consolidation.