A theoretical model of the hippocampal-cortical memory system motivated by physiological functions in the hippocampus

Based on the physiological evidence, we propose a hypothesis on how association and dissociation of event memories are made in the hippocampal-cortical memory system. It is postulated that the association/dissociation of memory is carried out by indexing the representations of events (memory contents) with temporal codes. The memory contents are supplied from the sensory association cortices, while the temporal codes are supplied from decision making/motivation area. The two inputs are mixed (indexing) in the ento-perirhinal area. Indexed signals are fed to hippocampus where connection/disconnection of memory contents occur depending on the kind of index. Finally, association/dissociation of event memories is made in the association cortex according to a covariance rule: two events memories are associated when direct cortio-cotical inputs and indirect inputs from the hippocampus are positively correlated through the consolidation made in hippocampus, and they are dissociated when two inputs are negatively correlated in consequence of the disconnection made in the hippocampus.