Facilitation of somatosensory average-evoked potentials in hysterical anesthesia and pain.

Psychophysiological inhibition theories of hysterical anesthesia were not supported in a study of habituation of scalp somatosensory average-evoked responses. Facilitation, rather than habituation, was found in responses contralaterial to the affected side with strong tactile stimuli in patients with hysterical heminesthesia or hemihypoesthesia, regional pain, and weakness. We suggest that the increase in response amplitude is related to the unusual congnitive set in these patients. Corticufugal influences on tactile sensory input might be mediated through increasing-excitation in a spinal-gating system.