Absolute and differential sensitivities to touch stimuli after spinal cord lesions in monkeys

Concurrent two-choice and go--no-go procedures were used to measure difference thresholds (DLs) for discrimination of touch intensities and absolute thresholds (RLs) for detection of light tactile stimuli by Macaca speciosa monkeys. Consistent with the classical proposition that the spinothalamic tracts of primates contain sufficient tactile input to support simple recognition of light skin contact, RLs were not affected by lesions of the ipsilateral dorsal column or by subsequent section of the ipsilateral dorsolateral column. There was, however, a clear dissociation of the effects of the spinal lesions on the absolute and difference thresholds. DLs were elevated ipsilaterally by lesions of the dorsal column and, after long periods of postoperative testing (more than 6 months), the DLs returned to postoperative levels. Subsequent interruption of the dorsolateral column again elevated DLs ipsilaterally and with extensive testing DLs again returned to preoperative levels.