Connectionists: memory, planning, and control of eye movement sequences and coordination of saccades and smooth pursuit

[Stephen Grossberg]

A great deal of brain is used for memory, planning, and control of movement sequences, including sequences of saccadic and smooth pursuit eye movements. Two recent articles, now available at http://cns.bu.edu/~steve , propose detailed neural models of how these brain systems are organized. In so doing, they propose functional roles for many brain regions and simulate how these regions may interact in real time to generate goal-oriented behaviors. 

A neural model of sequential movement planning and control of eye movements:
Item-order-rank working memory and saccade selection by the supplementary eye fields
Silver, M.R., Grossberg, S., Bullock, D., Histed, M.H., and Miller, E.K.
Neural Networks, in press

Abstract
How does working memory store multiple spatial positions to control sequences of eye movements, particularly 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 representations enable storage and recall of items that repeat at arbitrary list positions. Rank-related activity has been observed in many areas including the posterior parietal cortices (PPC), prefrontal cortices (PFC) and supplementary eye fields (SEF). The model shows how rank information, originating in PPC, may support rank-sensitive PFC working memory representations and how SEF may select saccades stored in working memory. It also proposes how SEF may interact with downstream regions such as the frontal eye fields (FEF) during memory-guided sequential saccade tasks, and how the basal ganglia (BG) may control the flow of information. Model simulations reproduce behavioral, anatomical and electrophysiological data under multiple experimental paradigms, including visually- and memory-guided single and sequential saccade tasks. Simulations reproduce behavioral data during two SEF microstimulation paradigms, showing that their seemingly inconsistent findings about saccade latency can be reconciled.
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Neural dynamics of saccadic and smooth pursuit eye movement coordination during visual tracking of unpredictably moving targets
Grossberg, S., Srihasam, K., and Bullock, D. 
Neural Networks, in press

Abstract
How does the brain coordinate saccadic and smooth pursuit eye movements to track objects that move in unpredictable directions and speeds? Saccadic eye movements rapidly foveate peripheral visual or auditory targets, and smooth pursuit eye movements keep the fovea pointed toward an attended moving target. Analyses of tracking data in monkeys and humans reveal systematic deviations from predictions of the simplest model of saccade-pursuit interactions, which would use no interactions other than common target selection and recruitment of shared motoneurons. Instead, saccadic and smooth pursuit movements cooperate to cancel errors of gaze position and velocity, and thus to maximize target visibility through time. How are these two systems coordinated to promote visual localization and identification of moving targets? How are saccades calibrated to correctly foveate a target despite its continued motion during the saccade? The neural model proposed here answers these questions. Modeled interactions encompass motion processing areas MT, MST, FPA, DLPN and NRTP; saccade planning and execution areas FEF, LIP, and SC; the saccadic generator in the brain stem; and the cerebellum. Simulations illustrate the model’s ability to functionally explain and quantitatively simulate anatomical, neurophysiological and behavioral data about coordinated saccade-pursuit tracking;
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