Comparison of forelimb and hindlimb motor deficits following dorsal column section in monkeys

Macaca speciosa monkeys were trained to acquire food reinforcement with motor responses that were defined by 4 different tasks. The effects of dorsal column lesions on the speed of these responses were compared for the forelimbs vs. the hindlimbs. Enduring impairments were not seen for any limb when the animal was required to accurately project a limb to different points in space, even with exclusion of visual guidance and with random variation of the start and stop points for each movement. Similarly, when the task required that the animals emit rapid response sequences, the forelimbs were impaired temporarily, but no long-term deficits were seen for the forelimbs or the hindlimbs. Although these impositions of spatial and temporal demands did not reveal striking disruptions of whole-limb movements, hindlimb grasp responses were shown to be impaired over long periods of postoperative testing. This corroborates previous findings for the forelimb and indicates that facility of distal extremity movement depends crucially on dorsal column-lemniscal input.