Rapid modulation of cortical proprioceptive activity induced by transient cutaneous deafferentation: neurophysiological evidence of short-term plasticity across different somatosensory modalities in humans.

Single cell recording in non-human primates shows plastic changes of cortical somatic representations across different types of somatic inputs originating from the same peripheral territory. In humans, muscle afferents from first dorsal interosseus are supplied by the ulnar nerve while the cutaneous territory overlying this muscle is supplied by the radial nerve. This peculiar anatomical nervous distribution allowed us to devise an experimental model which provided a unique opportunity to assess, in humans with a non-invasive technique, the functional relationships between cutaneous and muscle afferent inputs originating from the same peripheral territory. We recorded spinal, brainstem and cortical somatosensory potentials evoked by stimulation of muscle afferents of the right first dorsal interosseus before, during and after anaesthetic block of the sensitive branch of the ipsilateral radial nerve. Amplitude of parietal N20 and P27 and frontal N30 somatosensory evoked potential components showed an increase of amplitudes with more profound anaesthesia. Amplitudes returned to pre-anaesthetic values several minutes after anaesthesia. By contrast, spinal N13 and brainstem P14 potentials did not change throughout the experiment. Results show, for the first time in humans, that a transient cutaneous deafferentation may induce rapid modulation of cortical activity evoked by stimulation of muscle afferents originating in the anaesthetic territory.