Saturation in human somatosensory pathways.

The relationship between the size of an afferent volley and the size of the short-latency cerebral potential produced by the volley is not linear for purely cutaneous afferents, mixed cutaneous and muscle afferents or purely muscle afferents. The cerebral potential approaches a maximum when the responsible afferent input is 50% of maximum, while cerebral potentials of about half maximal size require an afferent volley of about one fifth of maximum. The relationship for sural (cutaneous) afferents rises less steeply. This saturation probably results from the convergence of the most rapidly conducting components in each afferent volley at sequential subcortical relay nuclei. The present data is compared with published data from animal experiments.