A neural model of sequential movement planning and control of eye movements: Rank-order working memory and saccade selection by the supplementary eye fields

How do working memory circuits store multiple spatial locations to control planned sequences of eye movements? How can working memory store and recall sequences when the same items repeat at multiple list positions, or ranks, during the sequence? An Item-Order-Rank model of working memory shows how rank-selective item representations enable correct sequential storage and recall of items that may repeat at arbitrary list positions. Rank-related neuronal activity has been observed throughout a number of brain regions including the posterior parietal cortices (PPC), prefrontal cortices (PFC) and supplementary eye fields (SEF). The model shows how rank information that originates in PPC may support rank-sensitive PFC working memory representations. Because PFC representations are rank-sensitive, items that occur at multiple positions within a sequence can be differentiated on the basis of their rank, and thus stored in parallel. SEF is known to be important for the production of sequences of memory-guided saccades and contains cells that fire before eye movements. The model explains how SEF can select saccades that are stored in working memory. The model also proposes how SEF interacts with downstream regions such as the frontal eye fields (FEF) during memory-guided sequential saccade tasks, and how the basal ganglia (BG) control the flow of information in cortical and subcortical areas.;Model simulations reproduce behavioral, anatomical and electrophysiological data under multiple experimental paradigms including visually- and memory-guided single and sequential saccade tasks. In addition, the model reproduces behavioral data during two different SEF microstimulation paradigms, and shows that their seemingly inconsistent findings about the impact of microstimulation on saccade latency can be reconciled within a single theoretical framework. By reproducing these data, the model makes predictions about the organization of working memory, its interaction with SEF as a system that selects an item to be performed next, and the way these two systems work with downstream oculomotor areas to generate sequential behavior.