[Corticothalamic Circuit Mechanisms Underlying the Regulation of Associative Memory]

Recent studies have shown compelling evidence that associative memories may not simply be stored as isolated sensory events but rather as integrated representations linking contexts, emotions, and experiences. This is in sharp contrast with the more traditional view that long-term memory storage is understood as a process in which hippocampal dependence gradually decreases and cortical circuits become increasingly responsible for remote memory retrieval. Recent studies have suggested that cortical engram cells are formed during learning and later change their functional state and retrievability. In this review, we discussed associative memory encoding, storage, and recall from the perspective of circuit states, rather than memory content alone. We focused on the corticothalamic circuits, which are increasingly being recognized as regulators of cortical activity, synchrony, and plasticity. Instead of directly storing memory content, thalamic inputs may shape the cortical conditions under which memory traces are formed, maintained, and retrieved. We also discussed synaptic plasticity and inhibitory gating as potential mechanisms that regulate engram retrieval. This framework provides a novel conceptual basis for understanding remote memory formation and memory impairment as disturbances in circuit states and retrievability.