Hippocampal-Cortical Circuits and Memory

This review examines how distributed neural circuits involving the hippocampus, entorhinal cortex, and neocortex collectively support learning and memory functions. The hippocampus and entorhinal cortex are densely and bidirectionally connected, forming a core circuit that supports the formation of episodic memories as well as spatial learning and navigation. Their interactions with neocortical regions underlie decision making and the transformation of episodic experience into abstract concepts. These functions are supported by precisely timed interactions between neuronal ensembles across distributed circuits, coordinated by neural oscillations. During learning and navigation, theta oscillations synchronize the firing of neuronal ensembles and mediate the flow of information across structures. During periods of rest and sleep, hippocampal sharp-wave ripples coordinate the reactivation of experience-related activity patterns. Sharp-wave ripples mediate the transfer of memory traces from the hippocampus to the neocortex and their long-term consolidation. Rather than a unidirectional transfer from hippocampus to neocortex, emerging evidence reveals continuous bidirectional interactions throughout memory encoding, consolidation, and retrieval. Critically, recurrent processing loops among the entorhinal cortex, hippocampus, and neocortex enable ongoing updating and integration of memory representations, challenging traditional sequential processing models and emphasizing the dynamic and interactive nature of these circuits.