Somatic sensory cortical projection areas excited y tactile stimulation of the cat: a triple representation.

1. The specific somatic sensory projection from the face to the cerebral cortex of the cat was investigated in two series of experiments. alpha-chloralose and Nembutal were the anaesthetics used.2. Evoked potentials, recorded at the cortical surface, were used in the first series for identifying three discrete projection areas from the face and forelimb. Two of these regions correspond to the established S I and S II projections. The third area, designated S III, was in the dorsal part of the anterior suprasylvian gyrus adjacent to the ansate sulcus.3. Single neurone analysis demonstrated that the cell populations responding to ;tactile' cutaneous stimulation of the face within each of the three specific somatic sensory projection areas had similar static functional properties. Most neurones observed had receptive fields restricted in size and were modality specific. Their receptive fields were mainly contralateral, although some had an ipsilateral extension. Fewer than 10% of cells observed in each specific cortical area were ;non-specific'. Such cells had extensive receptive fields and some of these fired to an auditory stimulus.4. Both field recording and single neurone analysis revealed a somatotopic projection to the S III area as well as to the S I and S II areas.