Electrophysiological analysis of interhemispheric relations in the second somatosensory cortex of the cat

Summary

• 1. Evoked potential studies done on chloralose anesthetized cats showed that potentials elicited by stimulation of the ipsilateral body surface and recorded in the second somatosensory cortex (SII) are mediated largely by contralateral somatosensory cortex by way of the corpus callosum; the ipsilateral posterior complex of the thalamus mediates only a small part of these potentials. Under the depressed conditions of barbiturate anesthesia only the ipsilateral posterior complex mediates these potentials.

• 2. Cells in anterior SII of unanesthetized, painlessly immobilized cats respond not only to light cutaneous stimulation but also to stimulation of contralateral somatosensory cortex. For some SII neurons stimulation of contralateral SII can inhibit discharges elicited by stimulation of the contralateral cutaneous receptive field.

• 3. All neurons excited by stimulation of contralateral SI and/or SII had bilateral receptive fields. These and other data suggest that much of the activity evoked by stimulation of the ipsilateral portion of a bilateral receptive field is mediated by contralateral somatosensory cortex by way of the corpus callosum.

• 4. Some neurons in SII which have small receptive fields on the contralateral forepaw can be discharged antidromically by stimulation of contralateral SII. Additional data show that large, slow wave potentials evoked by stimulation of the ipsilateral forepaw are mediated by the corpus callosum. Thus, contrary to expectations from anatomical studies, distal as well as proximal structures are represented in the topographical organization of the corpus callosum.