Pain perception in a man with total corpus callosum transection.

While classical and current theories of pain emphasize the critical role of central neural pathways that represent the contralateral body surface and cross within the spinal cord, the role of neural input representing the ipsilateral body surface is uncertain. In the present experiments with a complete corpus callosum-sectioned patient, both tactile and low intensity noxious stimuli (43-47 degrees C) ipsilateral to the responding cerebral hemisphere were poorly perceived and/or rated low on verbal and visual analogue scales (VAS). Surprisingly, however, high intensity noxious thermal stimuli (49-51 degrees C) were rated on verbal or visual analogue scales as very intense and unpleasant, thereby reflecting both sensory-discriminative and motivational-affective dimensions of pain. Thus, the pathways and mechanisms subserving this ipsilateral input have high thresholds for activation, but once activated are sufficient to evoke all of the critical dimensions of the experience of pain.