MECHANORECEPTIVE AFFERENTS EXHIBIT FUNCTIONALLY-SPECIFIC ACTIVITY-DEPENDENT CHANGES IN CONDUCTION-VELOCITY

Impulse activity in axons generates aftereffects on membrane excitabil ity that can alter the conduction velocity of subsequently conducted i mpulses. We used a computerized stimulus pattern (a 1 Hz stimulus peri od followed by a period of repeated short bursts at 200 Hz) to assess in vivo activity-dependent changes in conduction latency of functional ly identified rat cutaneous afferents conducting in the A beta range. Several different parameters of activity dependence were measured: bur st supernormality, the average increase in conduction latency followin g conditioning with a Single preceding impulse during high frequency b urst stimulation; burst subnormality, the average latency increase dur ing each burst, depression, a long-term increase in latency caused by the high frequency stimulation. The data show that different mechanose nsitive A beta afferents with overlapping resting conduction velocitie s exhibit activity-dependent changes in conduction latency that are ch aracteristic of their particular functions.