Finger movement deficits in the stumptail macaque following lesions of the fasciculus cuneatus.

Four stumptail macaques were trained to perform a key press with the index finger without associated movement of the adjacent (third) finger. Successful performance on this task required selective control over one finger (fractionation) and differential activation of muscles producing flexion or extension at different joints (multiarticulation). Following section of the fasciculus cuneatus (FC), a number of enduring deficits in finger movement capacities were observed. Over test periods of up to 2 years, fractionated key presses with the index finger could not be made, and the combination of flexion at the proximal joint with extension at the distal joints was absent. Coarticulated flexion at all the joints of each finger was substituted for the original multiarticulated, fractionated movements. We conclude that previous failures to observe impairments of finger movements following section of the dorsal columns (DCs) have resulted from the use of tasks that permit response substitution and therefore do not isolate specific movements for observation.