Architectonic parcellation of the temporal operculum in rhesus monkey and its projection pattern.

Abstract

Cyto- and myeloarchitectonic investigation of the temporal operculum and the exposed superior temporal gyrus was combined with a connection study of the projection fibers of the pertinent areas in the rhesus monkey. A belt-like organization of the auditory region with a koniocortex core (corresponding to AI) surrounded by belt areas was revealed. This organization principally resembled that of the auditory region of the cat (Rose and Woolsey, 1949; Woolsey, 1961) and that of other sensory regions (Sanides, 1972; Sanides and Krishnamurti, 1967). The belt is composed of one prokoniocortex area (proA, corresponding to AII) in parinsular location and of a caudal (paAc), lateral (paAlt) and rostral (paAr) parakoniocortex area. The latter has a particular character. It was found to be the target of thalamic projections of the caudalmost portion of GMpc. In contrast to the other parakonio areas it does not receive associations of the koniocortex. The belt areas, including the prokoniocortex, are ipsilaterally and transcallosally interconnected as in the somatic sensory (Jones and Powell, 1969a, b; Pandya and Kuypers, 1969; Pandya and Vignolo, 1969) and visual regions (Myers, 1962; Kuypers et al., 1965; Karol and Pandya, 1971). The koniocortex core is formed by two areas, Kam and Kalt, corresponding to the architectonic organization hitherto only known in man. The medial area (Kam) has a large number of homotopical callosal projections except at its medial border (to proA). The lateral area receives less callosal fibers, particularly most of its lateral portion is devoid of terminations. Since the belt areas are rich in callosal projections the supratemporal plane shows a pattern of three stripes of callosal terminations with two intermittent stripes void of terminations. While the projections of the koniocortex into the belt areas terminate prevalently in layer IV, the parakoniocortex sends fibers only into layers I and II of the koniocortex. This corresponds to results in somatic sensory (Pandya and McKenna, unpublished observations) and visual regions (Kuypers et al., 1965; Sanides and Vitzthum, 1965b; Spatz, personal communication). In contrast to other sensory regions the auditory koniocortex receives its exceptionally dense, homotopic callosal connections in the whole outer stratum with emphasis on layer III, as opposed to layer IV in the somatic sensory region.