Organization of a fourth somatosensory area of cortex in cat.

The organization of sensory representations in the cortex of the anterior ectosylvian sulcus (AES) of the cat was investigated using single-unit recording techniques. Somatic, auditory, and visual cells were found in the AES but were partially segregated. Somatic cells were concentrated in the rostral two-thirds of the sulcus, auditory cells were found in the caudal third, and visual cells were distributed along the fundus. A distinct, heretofore unknown, somatotopic representation of the body surface was observed in the AES and was designated SIV. The representation of the body in SIV extends along a rostrocaudal axis and the entire somatotopic map is inverted, with the head rostral and the hindquarters caudal. The representation of the paws extends over the lip of the sulcus to abut the paw representations in SII, and the SIV-SII boundary is marked by a reversal in the sequence of receptive fields along the AEG-AES. The SIV representation (SII) on the crown of the anterior ectosylvian gyrus (AEG). The somatotopic map in SII was found to extend further lateral on the AEG than shown by some investigations and it contains a double representation of the limbs: a large representation with the limbs having the opposite orientation to and abutting the SIV map and a smaller representation located more medial on the AEG and extending into the suprasylvian sulcus. The presence of this double representation may help to explain previous discrepancies regarding the overall orientation of the body in SII.