Closed- and open-loop handwriting performance in patients with multiple sclerosis

Normal subjects use an open-loop motor control strategy in handwriting, but they are able to switch to closed-loop motor control when the demands on a ccuracy increase. These closed-loop handwriting movements of normal subject s resemble the inefficient movements found in writing-impaired patients. Th e hypothesis that such movement deficits may in fact reflect the use of a c losed-loop strategy was tested in a group of writing-impaired patients with multiple sclerosis (MS). The handwriting movements of 10 MS patients and 2 0 control subjects were examined with a digitizing tablet. Three conditions were used: a standard writing task (expt 1), a closed-loop condition (expt 2), and an open-loop condition (expt 3). Individual stroke movements were analysed. Stroke duration and segmentation were increased for MS patients i n the standard writing task. The same was found for control subjects when t hey wrote under closed-loop conditions. However, under open-loop conditions , the handwriting movements of the MS patients were as fast and fluent as t hat of control subjects. The results support the hypothesis that the moveme nt characteristics of the writing-impaired MS patients reflect an inadequat e use of a closed-loop motor control strategy.