Synaptic Theory of Working Memory for Serial Order

Abstract

Working Memory (WM) enables the temporally-ordered maintenance of sequences of stimuli over short periods of time. This ability is critical for many cognitive and behavioral tasks. Despite its importance, however, how WM encodes, stores and retrieves information about serial order remains a major outstanding problem. Here, we extend our previously-proposed synaptic theory of WM to include synaptic augmentation, as experimentally observed at the same synapses that feature short-term facilitation. We find that synaptic augmentation leads to the emergence of a primacy gradient that can be used to reconstruct the order of presentation at recall, by an appropriate control of the background input to the WM network. The model reproduces prominent features of the behavior of human subjects recalling lists of items and makes a series of experimentally-testable predictions. Intriguingly, the model suggests that WM capacity limitations could result from a failure in retrieving, rather than encoding, information.