Our lab was the first to systematically describe this novel collective activity state in the hippocampus (Wolansky et al, 2006). It occurs during deep stages of slow-wave sleep and under anaesthesia and shows a dynamic correlation with slow EEG in the neocortex. Thus, it could be an activity-dependent platform for the coordination of hippocampal and cortical neuronal ensembles, a necessary component for the consolidation of declarative memories which occurs during sleep. We are currently investigating the mechanisms by which this hippocampal and neocortical coordination takes place in order to test its relevance to long-term memory formation. We are also testing how this and other rhythmic states may influence excitability throughout the hippocampus as a function of state and cycle of the ongoing oscillation. We are also testing the hypothesis that this state confers a lowered threshold for the hippocampus to general epileptiform activity due to the enhanced synchronization present.
