Department of Brain and Cognitive Sciences & Center for Learning and Memory, Massachusetts Institute of Technology
Coordinated interactions between hippocampal ripples and cortical spindles during slow-wave sleep
Sleep is characterized by a structured combination of neuronal oscillations. In the hippocampus, slow-wave sleep (SWS) is marked by transient high-frequency network oscillations (200 Hz ``ripples"), whereas neocortical SWS activity is organized into low-frequency delta (1-4 Hz) and spindle (7-14 Hz) waves. While these types of hippocampal and cortical oscillations have been studied extensively in isolation, the relationships between them remained unknown. Here, we demonstrate the existence of temporal correlations between hippocampal ripples and cortical spindles that are also reflected in the correlated activity of single neurons within these brain structures. Spindle-ripple episodes may thus constitute an important mode of cortico-hippocampal communication during sleep. This co-activation of hippocampal and neocortical pathways may be important for the process of memory consolidation, during which memories are gradually translated from short-term hippocampal to longer-term neocortical stores.