Deepak N. Pandya

Afferent cortical connections and architectonics of the superior temporal sulcus and surrounding cortex in the rhesus monkey.

A cyto- and myeloarchitectonic parcellation of the superior temporal sulcus and surrounding cortex in the rhesus monkey has been correlated with the pattern of afferent cortical connections from ipsilateral temporal, parietal and occipital lobes, studied by both silver impregnation and autoradiographic techniques. The results suggest a definite organization of this region. Subdivisions of the superior temporal gyrus are tied together in a precise sequence of connections beginning in primary auditory cortex. The inferotemporal area, which receives input from the lateral peristriate region, can also be divided into architectonic divisions, each of which is related to the others in a specific pattern of connections. Within the superior temporal sulcus several distinct areas exist. In the caudal reaches is found a region that receives input from both primary visual and visual association cortices. This zone is similar to the Clare-Bishop area of the cat. Other superior temporal sulcus zones receive input primarily from one limited area of association cortex. A strip in the upper bank receives input exclusively from the superior temporal gyrus. An area in the rostral lower bank has afferent connections mainly with the inferotemporal area, and a zone in the depth of the superior temporal sulcus receives fibers from a region within the lower bank of the intraparietal sulcus. Two additional zones, in the upper bank of the superior temporal sulcus, however, have multiple sources of cortical input: the peristriate belt, inferior parietal lobule and caudal superior temporal gyrus.

Some connections of the entorhinal (area 28) and perirhinal (area 35) cortices of the rhesus monkey. II. Frontal lobe afferents.

In this investigation the efferent projections from ventral temporal neocortical and limbic cortical areas to the entorhinal and perirhinal cortices have been investigated in the rhesus monkey using silver impregnation methods. It was observed that virtually all ventral temporal neocortical areas contribute some afferents to the transitional zones of periallocortex (perirhinal and prorhinal cortices) forming the walls of the rhinal sulcus. These areas in turn project medially to the entorhinal cortex and hippocampus. Additional direct sources of afferent input to the entorhinal cortex were found to originate in Brodmanns areas 51, 49 and 27, and Bonin and Baileys areas TF and TH. These connections have been characterized as final relays in multisynaptic cortico-cortical pathways linking the entorhinal cortex and, ultimately, hippocampus to the association areas of the frontal, parietal, temporal, and occipital lobes.

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

SummaryCyto- 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.

Some connections of the entorhinal (area 28) and perirhinal (area 35) cortices of the rhesus monkey. III. Efferent connections

In this investigation the efferent projections of the entorhinal and prorhinal cortices relative to their sites of termination in the hippocampus and fascia dentata were investigated in the rhesus monkey using experimental silver impregnation methods. Contrary to the often cited observations of Lorente de No, all entorhinal areas, including the laterally lying prorhinal cortex, were found to give rise to the perforant pathway, and furthermore, each cytoarchitectonically defined subarea was found to contribute a unique component. These perforant pathway components terminate in distinct regions of the dendritic zones of the fascia dentata granule cell and the hippocampal pyramidal cell. A previously undescribed projection to the prosubiculum and hippocampus has been found to originate from the prorhinal cortex which forms the medial wall of the rhinal sulcus along the lateral-most portion of the entorhinal cortex in the rhesus monkey. These results, in conjunction with our previous observations regarding differential afferents to the entorhinal cortex, indicate that specific afferent and efferent connections characterize each cytoarchitectonically definable subareas of this periallocortical region. Additionally, they indicate that the perforant pathway might be conceptualized as the final link in a multisynaptic series of connections instrumental in providing the hippocampus with potential modality specific and multimodal input.

Cortical Afferents to the Entorhinal Cortex of the Rhesus Monkey

Although the entorhinal cortex is a major contributor of afferents to the hippocampus and dentate gyrus, knowledge of its own afferents has been vague. Regions of both the frontal and temporal lobes were found to contribute afferents to this region of the brain. These afferents form probable multisynaptic links in pathways connecting the classical sensory areas of the cortex and the limbic system.

The topographical distribution of interhemispheric projections in the corpus callosum of the rhesus monkey

Summary The relative location of the interhemispheric cortical fibers within the corpus callosum was studied after callosal section in 7 rhesus monkeys with the silver impregnation techniques. Section of different parts of the corpus callosum resulted in strikingly dissimilar cortical projection patterns. On the basis of these patterns, the topography of the intracallosal fibers can be summarized as follows: (1) The rostral half of the corpus callosum carries the interhemispheric fibers to the various subdivisions of the frontal lobe (Fig. 5A and C). (2) The caudal half of the corpus callosum carries fibers to the parietal, temporal and occipital lobes and to the insulo-opercular region (Fig. 5B and C). (3) In the caudal half of the callosum, the parietal lobe fibers occupy a more rostral location than those of the temporal lobe. (4) The fibers to the precentral opercula cross the midline in the posterior half of the corpus callosum. (5) Fibers of the temporal lobe (with the exception of the prostriate area) and the insular region occupy the caudal part of the body of the corpus callosum. (6) The splenium contains the interhemispheric fibers to the occipital lobe and, in addition, those to the prostriate area.

Efferent cortico-cortical projections of the prefrontal cortex in the rhesus monkey.

Summary The efferent cortical projections of the prefrontal cortex were studied in rhesus monkeys using silver impregnation techniques. The projections from the prefrontal cortex are directed, in general, to the temporal, parietal and limbic (cingulate) cortex. However, different sectors of the prefrontal cortex, in particular the principal sulcus, show preferences for specific cortical regions (Fig. 4). The rostral part of the principal sulcus sends limited projections to the cingulate gyrus and to the rostral part of the superior temporal sulcus and gyrus. The middle sector has widespread connections with the cingulate gyrus as well as with the rostral and middle parts of the superior temporal sulcus. In contrast, the projections from the caudal third are directed to the parietal lobe and to the rostral as well as caudal parts of the superior temporal sulcus. Areas above and below the principal sulcus display poor reciprocal connectivity except for an area dorsal to the arcuate sulcus and the region between the fronto-orbital and arcuate sulci. The orbital cortex receives projections primarily from the lower bank of the principal sulcus and from the area below it, but few, if any, projections from the upper bank and regions dorsal to it.

Some cortical projections to the parahippocampal area in the rhesus monkey.

Abstract Using silver impregnation techniques to trace cortical connections in rhesus monkeys subject to ablations of various parts of posterior “association” cortex, several specific projections to sectors of the parahippocampal area have been found. Area TF is the recipient of projections from the caudal inferior parietal lobule; area TH has afferent connections with the rostroventral superior temporal gyrus; both areas TF and TH together receive input from the lateral and ventral peristriate belt. In addition, the inferior temporal gyrus also projects to areas TF-TH of von Bonin and Bailey as well as the cortex in the banks of the rhinal fissure. The possible significance of these projections in terms of sensory-limbic connections and sensory convergence is discussed.

Posterior cingulate and retrosplenial cortex connections of the caudal superior temporal region in the rhesus monkey

The rostral part of the superior temporal gyrus (STG) is known to project to ventral temporal cortex, but analogous paralimbic connections of the caudal STG have received comparatively less attention. The present study of the connections of the STG with medial paralimbic cortex showed that the caudal part of the STG (area Tpt and caudal area paAlt) and adjacent cortex of the upper bank of the superior temporal sulcus (caudal area TPO) have reciprocal connections with the caudal cingulate gyrus (areas 23a, b and c), retrosplenial cortex (area 30), and area 31. By contrast, cortex of the rostral-to-mid STG (areas Ts2, Ts3, and the rostral part of area paAlt) and adjacent upper bank of the STS (mid-area TPO) have few, if any, such interconnections. It is suggested that this connectional pattern of the caudal STG is consistent with its putative role of localizing sounds in space as proposed in recent studies.