Input-output relation of the somatosensory system for mechanical air-puff stimulation of the index finger in man.

This study examined input-output relation of the somatosensory system in response to mechanical air-puff stimuli applied to the volar aspect of the tip of the index finger. Compound sensory nerve action potentials (SNAPs) from the median nerve at the wrist and cerebral somatosensory evoked potentials (SEPs) were simultaneously recorded at six levels of stimulus intensity above threshold. Using the time-integral of the SNAPs and SEPs as measures of peripheral and central neural activity, a strongly accelerating power function with an exponent of 1.35 was found to describe peripheral neural function, while central neural function was described by a negatively accelerating function with a power exponent of 0.50, suggesting suppression of SEPs by recruitment of units with increasing stimulus intensity. It was concluded that input-output relation of the somatosensory system can be described by a decelerating power function with the exponent of 0.37.