In experiment 1, two Macaca speciosa monkeys were trained to discriminate two forms of tactile stimulation to the legs or feet. Both stimuli were delivered by perpendicular contact of bristles to the skin, but in one case the bristles were stroked across the skin as the brush was removed, and on the other trials the brush was removed as it had been applied, with minimal movement of the bristles over the skin. This test of tactile movement detection revealed only slight, transient impairment following ipsilateral section of the dorsal spinal columns. A more severe deficit was observed after ipsilateral dorsal quadrant lesions, but recovery to a high level of performance was observed. In experiment 2, three monkeys learned to discriminate proximal vs. distal movement of the bristles over the hairy skin of either leg. Dorsal column lesions in these monkeys produced an unusually enduring inability to discriminate direction of tactile stimulus motion. This result is discussed in relation to recent theoretical statements about the importance of dorsal column transmission for perception of passively received tactile stimuli.
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