Abstract
To investigate the functional role of the striatum in visuo-motor adaptation, we extend the DIRECT-model for visuo-motor reaching movements formulated by Bullock et al.(J Cogn Neurosci 5:408435,1993) through two parallel loops, each modeling a distinct contribution of the corticocerebellarthalamocortical and the corticostriatothalamocortical networks to visuo-motor adaptation. Based on evidence of Robertson and Miall(Neuroreport 10(5): 10291034, 1999), we implement the function of the corticocerebellarthalamocortical loop as a module that gradually adapts to small changes in sensorimotor relationships. The corticostriatothalamocortical loop on the other hand is hypothesized to act as an adaptive search element, guessing new sensorimotor-transformations and reinforcing successful guesses while punishing unsuccessful ones. In a first step, we show that the model reproduces trajectories and error curves of healthy subjects in a two dimensional center-out reaching task with rotated screen cursor visual feedback. In a second step, we disable learning processes in the corticostriato thalamocortical loop to simulate subjects with Parkinsons disease (PD), and show that this leads to error curves typical of subjects with PD. We conclude that the results support our hypothesis, i.e., that the role of the corticostriatothalamocortical loop in visuo-motor adaptation is that of an adaptive search element.