Physiological Signature of Memory Age in the Prefrontal-Hippocampal Circuit

Abstract

The long-term storage of episodic memory requires communication between prefrontal cortex and hippocampus. However, how consolidation alters dynamic interactions between these regions during subsequent recall remains unknown. Here we performed simultaneous electrophysiological recordings from anterior cingulate cortex (ACC) and hippocampal CA1 in mice during recall of recent and remote contextual fear memory. We found that in contrast to recent memory, remote memory recall was accompanied by increased ACC-CA1 synchronization at multiple frequency bands. The augmented ACC-CA1 interaction was associated with strengthened coupling among distally spaced CA1 neurons, suggesting an ACC-driven organization of a sparse code. This robust shift in physiology permitted a support vector machine classifier to accurately determine memory age based on the ACC-CA1 synchronization pattern. Our findings reveal that memory consolidation alters the dynamic coupling of the prefrontal-hippocampal circuit and results in a physiological signature of memory age.

Keywords: prefrontal cortex, hippocampus, contextual fear conditioning, remote memory, theta oscillation, gamma oscillation, cross-frequency coupling, spike phase-locking, co-firing, machine learning