The gain of initial somatosensory evoked potentials alters with practice of an accurate motor task

The gain of somatosensory afferent paths from the lower limb to the cerebra l cortex was investigated during the acquisition of one target location dur ing plantar flexion. Sensory gain was measured as the magnitude of somatose nsory evoked potentials (SEPs) following electrical stimulation of a periph eral nerve in the lower limb, and was recorded from the scalp. We hypothesi zed gain attenuation of SEPs from sensory paths serving the limb segment re sponsible for target acquisition. SEP gain was studied as subjects plantar flexed about the anide to a target that was 15 degrees beyond the occurrenc e of a cutaneous stimulus (cue) to the lateral border of the foot. The 'cue ' was either fixed in one location or could appear at one of three position s in space. SEP gain was tested during practice and with task acquisition. Electroencephalographic (EEG) recordings were made of primary and secondary complexes of cortical SEPs. from sural and tibial nerve stimulation, with 30-40 samples averaged per subject-condition. Electromyographic (EMG) recor ds were made of soleus muscle H-reflexes and M-waves. Target acquisition wa s recorded as percent correct hits. The results showed significant attenuat ion in sural and tibial nerve primary SEPs with task acquisition when the c ue was fixed or varied in movement space (P < 0.05). Secondary SEPs from ti bial nerve followed this pattern. Spinal H-reflexes only attenuated with mo vement per se. We conclude that the CNS preferentially reduces the cerebral inflow of sensory information once such a motor task has been successfully acquired. (C) 2001 Elsevier Science B.V. All rights reserved.