Coherent reactivation in hippocampal – ventral striatal ensembles during sleep.
1. Center for Neuroscience, SILS, Universiteit van Amsterdam, the Netherlands
2. Arizona Research Laboratories, Department of Neural Systems, Memory and Aging, Tucson, AZ
Memory consolidation likely involves the strengthening of specific connections within and between different brain areas. Inter-area reactivation of neuronal patterns during post-experiential rest and sleep periods may contribute significantly to this process. The hippocampus (HC) and ventral striatum (VS) are anatomically connected, both exhibit reactivation individually and process information crucial for guiding goal-directed behavior, i.e. information on spatial context and reinforcement contingencies, respectively. The finding that replay in the VS is closely associated with the occurrence of sharp wave/ripple complexes in the hippocampal EEG, prompted us to examine ensemble interactions between these structures during reactivation. Spike trains and local field potentials from the hippocampal CA1 area and the VS were recorded simultaneously from 4 rats when they performed a reward searching task on a triangular track flanked by two periods of rest. A partial correlation analysis showed significant reactivation of HC-VS cell-pairs across 21 sessions containing a total of 3215 pairs (explained variance, EV 10.5 ± 3.3, Reverse EV 1.9 ± 0.7, Wilcoxon’s matched pairs signed rank, WMPSR p < 0.01). Joint replay occurred predominantly during slow wave sleep while no evidence for this process was found within REM sleep (SWS: EV 6.8 ± 2.1, REV 0.9 ± 0.3 WMPSR p < 0.01, REM EV: 0.6 ± 0.3, REV 0.4 ± 0.2). Cross-structural reactivation may provide a mechanism for coordination of replay throughout the brain in which the hippocampus might playl a leading role. It also might serve to bind information reactivated in different areas to enable the composition or reconstruction of a complete memory trace.
Grant/Other Support: HFSP Grant RGP0127/2001-B; VICI grant 918.46.609; MH046823.
Key Words: memory; consolidation; nucleus accumbens; reward; tetrode; motivation