Integration and Segregation of Activity in Neocortex-Hippocampus by Slow Oscillations
Center for Molecular and Behavioral Neuroscience
Brain systems communicate by means of neuronal oscillations at multiple temporal and spatial scales. Slow oscillations involve large neocortical areas, alternating between activity (UP) and silence (DOWN) states (Steriade et al, 1993). During slow wave sleep DOWN states in neocortex are associated with decrease of CA1 unit activity and probability of ripples (Sirota et al, 2003; Battaglia et al, 2004). To explore this phenomenon and its mechanism we recorded intracellular membrane potential in anesthetized rats from neurons in the neocortex, entorhinal cortex (EC), subiculum and hippocampus with simultaneous recordings of the local field potential and units from hippocampal subfields. We find that slow oscillation and associated DOWN-UP states are synchronous between the neocortex, entorhinal and subicular cortices. In contrast, fluctuations of the membrane potential of hippocampal cells showed a unimodal distribution, but were coherent to the neocortical slow oscillation. Analysis of the preferred phases of depolarization, unit firing and local gamma and sharpwaves revealed differential recruitment of hippocampal network by the slow oscillation. Dentate gyrus network was directly driven by the EC during UP state, intrinsic activity in the CA3 network self-organized during the DOWN state, and activity in CA1 was affected by both EC in the UP state and CA3 activity in the DOWN state. Analysis of simultaneous recordings in hippocampus and neocortex and entorhinal cortex in non-anesthetized rats during SWS confirms these findings. Thus, neo/paleocortical and hippocampal networks periodically reset, self-organize and temporally coordinate their local activity within the slow oscillation.
Last Modified: Jan 18, 2006
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