Despite several decades of research the precise neuronal mechanisms underlying episodic memory, our memory of experienced events in our lives, remain unclear. We recently suggested that episodic memories are best represented as sequences of neural activity patterns and proposed specific contributions of the hippocampal subregions to the storage and retrieval of neuronal sequences. One central feature of the CRISP theory is that hippocampal area CA3 intrinsically produces sequences. During memory encoding, intrinsic CA3 sequences are associated with sequences that are driven by sensory inputs. During memory retrieval, intrinsic CA3 sequences have to be reactivated based on partial, noisy cues. Each element in the retrieved sequence, a CA3 pattern, in turn leads to the retrieval of the associated CA1 pattern. This CA3-CA1 association for pattern completion and therefore more accurate memory recall. In CRISP, the role of the dentate gyrus is to help initiate different intrinsic sequences in CA3, even for similar input sequences, i.e. sequence separation. Using neural network models, we investigate under which conditions the hippocampal circuit can perform the hypothesized functions robustly, so that neuronal sequences are stored and robustly retrieved.
Hippocampal Reactivation Extends for Several Hours Following Novel Experience