ACC Theta Improves Hippocampal Contextual Processing during Remote Recall

Consolidation studies show that, over time, memory recall becomes independent of the medial temporal lobes. 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 hypothesize that interactions between the ACC and hippocampal area CA1 will change as memories became more remote. Animals are re-exposed to multiple environments at different retention intervals. During remote recall, ACC-CA1 theta coherence increases, with the ACC leading area CA1. ACC theta regulates unit spike timing, gamma oscillations, and ensemble and single-neuron information coding in CA1. Over the course of consolidation, the strength and prevalence of ACC theta modulation grow, leading to richer environmental context representations in CA1. These data are consistent with the transference of contextual memory dependence to the ACC and indicate that remote memories are retrieved via ACC-driven oscillatory coupling with CA1.