ACC Theta Improves Hippocampal Contextual Processing During Remote Recall

Abstract

Standard consolidation theory argues that over time memory recall becomes independent of the hippocampus. Multiple lines of research show that the medial frontal cortex, including the anterior cingulate cortex (ACC), is involved with contextual information processing and remote recall. We hypothesized interactions between the ACC and hippocampal area CA1 would change as memories became more remote. Animals were re-exposed to multiple environments at different retention intervals and during remote recall ACC-CA1 theta coherence increased. Theta-mediated communication from the ACC to CA1 regulates unit spike timing, gamma oscillations, and ensemble and single neuron information coding. Furthermore, since all our analyses pointed to the effects originating in the ACC, it is consistent with how one would expect memory readout to occur according to the standard consolidation model. In this case, the readout of the memory begins in the ACC and the effects can be observed in the CA1.