Interfering cutaneous stimulation and the muscle afferent contribution to cortical potentials.

Cerebral potentials were recorded in response to selective stimulation using microelectrodes of muscle afferents in motor fascicles innervating the intrinsic muscles of the foot or at the motor point of abductor hallucis. The early components of these potentials (P40, N50 and P60) were consistently attenuated by continuous tactile stimulation of related skin areas and by electrical stimulation of digital nerves, timed so that the digital volley reached cortex approximately 5 msec before the muscle afferent volley. The same conditioning cutaneous inputs also attenuated the cerebral potentials evoked by selective stimulation of cutaneous afferents. These findings confirm that there are intermodality and intramodality interactions between low-threshold cutaneous and muscle afferents and between cutaneous afferents, respectively. The findings indicate that 'interference phenomena' (Kakigi and Jones 1986) can occur between different afferent modalities, and within any one modality, and cannot be used to determine the afferent species responsible for the test evoked potential.