Proprioceptive modulation of somatosensory evoked potentials during active or passive finger movements in man.

The effects of active and passive finger movements on somatosensory potentials evoked by stimulation of the median nerve at the wrist or of finger I were investigated in 15 healthy volunteers. As compared to the resting condition, both active and passive movements of the stimulated hand fingers induced a marked reduction in the amplitude of the primary cerebral response (N20-P25 complex) as well as of the N17 SEP component, which is supposed to reflect the activity of the thalamo-cortical radiation. The following cerebral SEP components, within 100 ms after the stimulus, were also depressed during motor activity. Neither N11 nor N13 components of the cervical response, reflecting the activation of dorsal columns and dorsal column nuclei respectively, were modified. The SEP changes induced by active or passive movements were absent after ischaemic block of large group I afferent fibers from the hand, thus suggesting the relevance of the feedback generated by such peripheral afferents during movement. The results indicate that the activation of peripheral receptors (probably muscle spindle endings) during both active and passive finger movement would induce a gating effect at both cortical and subcortical (thalamic) level, which might modulate selectively the different sensory inputs to the cortex.