COMPARISON OF REACTIVATION AND TEMPORAL COMPRESSION OF SPIKE PATTERNS IN THE RAT HIPPOCAMPUS AND PREFRONTAL CORTEX

D.R. Euston ¹*; M.R. Bower ²; B.L. McNaughton ¹

1. NSMA , Univ Arizona, Tucson, AZ, USA
2. Comparative Medicine, Stanford Univ, Stanford, CA, USA

Theories of memory consolidation suggest that, during sleep, the hippocampus drives replay of cortical spike patterns corresponding to previous experiences, a process known as “reactivation”. To understand this process better, reactivation in the prefrontal cortex and hippocampus were compared. Four rats were trained to run to a sequence of locations around the perimeter of a 1.5 m arena (Bower et al., 2005). The rats learned the task well, typically completing 100 cycles of the 8-element sequence in a 50 minute period and producing highly stereotyped trajectories. Each behavioral session was interposed between two 20-30 minute rest/sleep periods. 30-60 cells per session were simultaneously recorded from either the dorsal hippocampus or medial prefrontal cortex. Cells that were highly correlated on the task tended to be more highly correlated in the subsequent sleep than in the preceding sleep (higher EV; Kudrimoti et al., 1999), particularly in prefrontal cortex. Because of the repetitiveness of the task, the spike train cross-correlograms during behavior showed patterns of peaks and troughs spanning 15 seconds or more. In the prefrontal cortex, this cross-correlation structure was preserved during subsequent sleep in an 800 ms window, but temporally compressed by a factor of approximately 7, indicating that spike patterns were replaying at an accelerated pace. In the hippocampus the window was significantly narrower, possibly because reactivation occurs within the temporal limits of hippocampal sharp waves. If cortical reactivation is triggered by the hippocampus, as theory suggests, the temporal patterns in the cortex may continue their replay after hippocampal input has ceased, evolving under their own intrinsic dynamics.

Support Contributed By: MH046823 & JST CREST

Key words: consolidation, memory, multielectrode, sleep