CYTOARCHITECTURE AND RESPONSIVENESS OF THE MEDIAL ANSATE REGION OF THE CAT PRIMARY SOMATOSENSORY CORTEX

To understand its relationship to somatosensory areas in other species , we studied the rostral bank of the medial ansate sulcus in adult cat s. Neurons in the shoulder and upper part of the sulcal wall responded to low-threshold cutaneous stimuli much like neurons on the crown of the gyrus, whereas neurons in some deeper portions of the sulcus requi red more intense but innocuous somatic stimuli. Because we found much of the body surface re-represented in this area, we suggest that, besi des the representation in area 3b, there is another cutaneous represen tation of the hindlimb and trunk located on the gyral crown near the m edial end of the medial ansate sulcus and of the forelimb and trunk wi thin the medial ansate sulcus. Posterior to this second cutaneous repr esentation, many parts of the body were also represented in regions ac tivated by more intense stimuli and having a different cytoarchitectur e, suggesting that they were part of another body representation. Area 3b and the shoulder of the gyrus were distinguished by relatively int ense acetylcholinesterase staining of layers III and IV. In the wall o f the sulcus, all layers except layer I were uniformly stained to a po int where electrophysiological recordings showed the cortex to be unre sponsive, whereupon the outer two-thirds of layer I became very pale. Neurons activated by afferents from knee joints were found only in a s mall area; we did not find a mediolateral band serving joint afferents as is reported in primates. These data suggest that cat somatosensory cortex differs in some ways from primates but that it contains multip le representations of the body, as do most other mammals. (C) 1994 Wil ey-Liss, Inc.