A Cortico-Spinal Model of Reaching and Proprioception under Multiple Task Constraints

Paul Cisek, Stephen Grossberg, Daniel Bullock
1998 Journal of Cognitive Neuroscience  
A model of cortico-spinal trajectory generation for voluntary reaching movements is developed to functionally interpret a broad range of behavioral, physiological, and anatomical data. The model simulates how arm movements achieve their remarkable efficiency and accuracy in response to widely varying positional, speed, and force constraints. A key issue in arm movement control is how the brain copes with such a wide range of movement contexts. The model suggests how the brain may set automatic
more » ... nd volitional gating mechanisms to vary the balance of static and dynamic feedback information to guide the movement command and to compensate for external forces. For example, with increasing movement speed, the system shifts from a feedback position controller to a feedforward trajectory generator with superimposed dynamics compensation. Simulations of the model illustrate how it reproduces the effects of elastic loads on fast movements, endpoint errors in Coriolis fields, and several effects of muscle tendon vibration, including tonic and antagonist vibration reflexes, position and movement illusions, effects of obstructing the tonic vibration reflex, and reaching undershoots caused by antagonist vibration. . INTRODUcnON Empirical research on the control of primate reaching movements has ranged from studies of muscle activity through recordings from cells in the cerebral cortex of monkeys performing reaching tasks to observations of human movements in unusual force environments. As part of an attempt to unify these diverse experimental data, Bullock, Cisek, and Grossberg (1998) proposed a computational model that incorporates model neurons corresponding to identified cortical cell types in a circuit that reflects known anatomical connectivity (Figure 1) . The model maintains accurate proprioception while controlling voluntary reaches to spatial targets, exertion of force against obstacles, posture despite perturbations, compliance with an imposed movement, and static and inertial load compensations. Computer simulations in Bullock et al. (1998) showed that properties of model elements correspond to the dynamic properties of many known cell types in areas 4 and 5 of the cerebral cortex. Among these properties are delay period activation, response profiles during movement, kinematic and kinetic sensitivities, and latency of activity onset (Alexander &
doi:10.1162/089892998562852 pmid:9712674 fatcat:zbpybdkyyvdfbol2z7t4umxeyu