Target- and state-dependent information flow of hippocampal ripples to the neocortex during slow wave activity

Ripples occur in the hippocampus, whereas slow waves are dominant in the neocortex during anesthesia. Neocortical slow waves consist of Up and Down states, which are not necessarily synchronized across neocortical regions. However, the precise temporal relationship between ripples and slow waves across multiple neocortical regions remains unclear. We recorded ripples from the hippocampus and slow waves from the medial prefrontal and retrosplenial cortices. We found that ripples were more phase-locked with prefrontal slow waves and elongated when both neocortical regions were in Up states. These results provide a biophysical platform for understanding the hippocampal-cortical dialogue for memory consolidation during sleep.