Neural Mechanisms of the Maintenance and Manipulation of Gustatory Working Memory in Orbitofrontal Cortex

Orbitofrontal cortex (OFC) is involved in flavor perception and executive functions of chemical sensations. It integrates multiple sensory modalities to perceive the flavor of foods, and organizes sensory information in selection of behavioral strategies. A recent study has reported that gustatory working memory (WM) is maintained in the OFC of rhesus monkeys. However, the maintenance mechanism remains unclear. Moreover, the manipulation mechanism, or how WM is utilized to guide behavior, also poorly understood. To address these issues, we are concerned with a delayed match-to-sample (DMS) task, and present a model for WM maintenance and manipulation in OFC. The model consists of the networks of gustatory cortex, OFC, and a decision layer. We show that gustatory WM is represented by a sparse activity of OFC neurons, elicited by short-term synaptic plasticity. The intermittent spiking in the sparse activity prevents from reducing the efficacy of short-term synaptic plasticity. The sparse activity codes WM in a functionally latent state, and retrieves WM in a functionally active state as it is needed. In contrast, top-down signals from OFC allows GC neurons to represent the gustatory information relevant to the WM maintained in OFC. We also present a comparison mechanism of a sample and a test stimulus, separated by a delay period. Furthermore, we offer the mechanism by which the synaptic structures of the neural circuits involved in the DMS task are generated via the task training. The results provide a unified view of how WM maintenance is linked to its manipulation.