Lack of a proprioceptive deficit after dorsal column lesions in monkeys

Previous psychophysical examinations of the effects of dorsal column (DC) lesions on proprioception of the lower extremity have not revealed disturbances in proprioception, and there have been no similar experiments for the upper extremity. To evaluate the effect of DC lesions on upper extremity proprioception, we tested two monkeys with a variation of the typical clinical test for position sense. This test required the monkeys to detect the direction of a passive displacement of the finger. We identified proprioceptive deficits in one monkey following a DC lesion, but only when the finger was displaced with a small (< 14 degrees), slow (< 7 degrees/sec) movement. When we included displacements of all sizes and velocities in the analysis, performance was unaffected by the DC lesions in either monkey. Since the standard test for proprioception does not specify the speed and size of movements, we conclude that this test is not a valid method for estimating damage to the DCs.