Time-locked Multiregional Retroactivation: a Systems-level Proposal for the Neural Substrates of Recall and Recognition

This article outlines a theoretical framework for the understanding of the neural basis of memory and consciousness, at systems level. It proposes an architecture constituted by: (1) neuron ensembles located in multiple and separate regions of primary and first-order sensory association cortices ("early cortices") and motor cortices; they contain representations of feature fragments inscribed as patterns of activity originally engaged by perceptuomotor interactions; (2) neuron ensembles located downstream from the former throughout single modality cortices (local convergence zones); they inscribe amodal records of the combinatorial arrangement of feature fragments that occurred synchronously during the experience of entities or events in sector (1); (3) neuron ensembles located downstream from the former throughout higher-order association cortices (non-local convergence zones), which inscribe amodal records of the synchronous combinatorial arrangements of local convergence zones during the experience of entities and events in sector (1); (4) feed-forward and feedback projections interlocking reciprocally the neuron ensembles in (1) with those in (2) according to a many-to-one (feed-forward) and one-to-many (feedback) principle. I propose that (a) recall of entities and events occurs when the neuron ensembles in (1) are activated in time-locked fashion; (b) the synchronous activations are directed from convergence zones in (2) and (3); and (c) the process of reactivation is triggered from firing in convergence zones and mediated by feedback projections. This proposal rejects a single anatomical site for the integration of memory and motor processes and a single store for the meaning of entities of events. Meaning is reached by time-locked multiregional retroactivation of widespread fragment records. Only the latter records can become contents of consciousness.