Ipsilateral cortical connections of motor, premotor, frontal eye, and posterior parietal fields in a prosimian primate, Otolemur garnetti

The ipsilateral connections of motor areas of galagos were determined by injecting tracers into primary motor cortex (M1), dorsal premotor area (PMD), ventral premotor area (PMV), supplementary motor area (SMA), and frontal eye field (FEF). Other injections were placed in frontal cortex and in posterior parietal cortex to define the connections of motor areas further. Intracortical microstimulation was used to identify injection sites and map motor areas in the same cases. The major connections of M1 were with premotor cortex, SMA, cingulate motor cortex, somatosensory areas 3a and 1, and the rostral half of posterior parietal cortex. Less dense connections were with the second (S2) and parietal ventral (PV) somatosensory areas. Injections in PMD labeled neurons across a mediolateral belt of posterior parietal cortex extending from the medial wall to lateral to the intraparietal sulcus. Other inputs came from SMA, M1, PMV, and adjoining frontal cortex. PMV injections labeled neurons across a large zone of posterior parietal cortex, overlapping the region projecting to PMD but centered more laterally. Other connections were with M1, PMD, and frontal cortex and sparsely with somatosensory areas 3a, 1-2, S2, and PV. SMA connections were with medial posterior parietal cortex, cingulate motor cortex, PMD, and PMV. An FEF injection labeled neurons in the intraparietal sulcus. Injections in posterior parietal cortex revealed that the rostral half receives somatosensory inputs, whereas the caudal half receives visual inputs. Thus, posterior parietal cortex links visual and somatosensory areas with motor fields of frontal cortex.     

Interconnections between the prefrontal cortex and the premotor areas in the frontal lobe

We examined interconnections between a portion of the prefrontal cortex and the premotor areas in the frontal lobe to provide insights into the routes by which the prefrontal cortex gains access to the primary motor cortex and the central control of movement. We placed multiple injections of one retrograde tracer in the arm area of the primary motor cortex to define the premotor areas in the frontal lobe. Then, in the same animal, we placed multiple injections of another retrograde tracer in and around the principal sulcus (Walker's area 46). This double labeling strategy enabled us to determine which premotor areas are interconnected with the prefrontal cortex. There are three major results of this study. First, we found that five of the six premotor areas in the frontal lobe are interconnected with the dorsolateral prefrontal cortex. Second, the major site for interactions between the prefrontal cortex and the premotor areas is the ventral premotor area. Third, the prefrontal cortex is interconnected with only a portion of the arm representation in three premotor areas (supplementary motor area, the caudal cingulate motor area on the ventral bank of the cingulate sulcus, and the dorsal premotor area), whereas it is interconnected with the entire arm representation in the ventral premotor area and the rostral cingulate motor area. These observations indicate that the output of the prefrontal cortex targets specific premotor areas and even subregions within individual premotor areas.     

Cortical connections of the inferior arcuate sulcus cortex in the macaque brain

Injections of the retrograde/anterograde tracers Wheat Germ Agglutinin-Horseradish peroxidase (WGA-HRP) into the cortex along the banks of the inferior limb of the arcuate sulcus in the cortex of 4 macaque monkeys (Macaca fascicularis) were used to investigate its cortico-cortical connections. All injections produced transported label within the sulcus principalis, the ventral lateral prefrontal cortex, the anterior cingulate sulcus and the dorsal insular cortex. The distribution of label within each of these areas differed slightly depending on the injection site. Injections along the caudal bank of the inferior arcuate sulcus label premotor, supplementary motor, and precentral motor areas but produce relatively sparse prefrontal labeling. Posteriorly label is transported to the inferior parietal cortex and the dorsal opercular bank of the Sylvian fissure. Injections along the rostral bank of the sulcus do not label motor areas but produce labeling in dorsal, lateral and orbital prefrontal areas, and in cortex along the ventral bank of the superior branch of the arcuate sulcus. Posteriorly label is transported to cortical areas in the superior temporal gyrus including the dorsal bank of the superior temporal sulcus. The more dorsal rostral bank injection produced both superior temporal and some sparse inferior parietal labeling and the more ventral rostral bank injection produced extensive superior temporal labeling but no parietal labeling. No labeling was ever seen in cortex ventral to the fundus of the superior temporal sulcus. Although other auditory recipient prefrontal areas have been reported, this is the first demonstration of a region chiefly devoted to auditory connections within the ventral frontal cortex. Its adjacency to areas associated with vocal muscle movement, and its connections to midline cortical areas associated with vocal functions in both primates and humans may provide important clues to the organization of Broca's language area.     

Posterior parietal cortex in rhesus monkey: I. Parcellation of areas based on distinctive limbic and sensory corticocortical connections

Injections of HRP-WGA in four cytoarchitectonic subdivisions of the posterior parietal cortex in rhesus monkeys allowed us to examine the major limbic and sensory afferent and efferent connections of each area. Area 7a (the caudal part of the posterior parietal lobe) is reciprocally interconnected with multiple visual-related areas: the superior temporal polysensory area (STP) in the upper bank of the superior temporal sulcus (STS), visual motion areas in the upper bank of STS, the dorsal prelunate gyrus, and portions of V2 and the parieto-occipital (PO) area. Area 7a is also heavily interconnected with limbic areas: the ventral posterior cingulate cortex, agranular retrosplenial cortex, caudomedial lobule, the parahippocampal gyrus, and the presubiculum. By contrast, the adjacent subdivision, area 7ip (within the posterior bank of the intraparietal sulcus), has few limbic connections but projects to and receives projections from widespread visual areas different than those that are connected with area 7a: the ventral bank and fundus of the STS including part of the STP cortex and the inferotemporal cortex (IT), areas MT (middle temporal) and possibly MTp (MT peripheral) and FST (fundal superior temporal) and portions of V2, V3v, V3d, V3A, V4, PO, and the inferior temporal (IT) convexity cortex. The connections between posterior parietal areas and visual areas located on the medial surface of the occipital and parieto-occipital cortex, containing peripheral representations of the visual field (V2, V3, PO), represent a major previously unrecognized source of visual inputs to the parietal association cortex. Area 7b (the rostral part of the posterior parietal lobe) was distinctive among parietal areas in its selective association with somatosensory-related areas: S1, S2, 5, the vestibular cortex, the insular cortex, and the supplementary somatosensory area (SSA). Like 7ip, area 7b had few limbic associations. Area 7m (on the medial posterior parietal cortex) has its own topographically distinct connections with the limbic (the posterior ventral bank of the cingulate sulcus, granular retrosplenial cortex, and presubiculum), visual (V2, PO, and the visual motion cortex in the upper bank of the STS), and somatosensory (SSA, and area 5) cortical areas. Each parietal subdivision is extensively interconnected with areas of the contralateral hemisphere, including both the homotopic cortex and widespread heterotopic areas. Indeed, each area is interconnected with as many areas of the contralateral hemisphere as it is within the ipsilateral one, though less intensively. This pattern of distribution allows for a remarkable degree of interhemispheric integration.(ABSTRACT TRUNCATED AT 400 WORDS)     

Early coding of reaching: frontal and parietal association connections of parieto-occipital cortex

The ipsilateral association connections of the cortex of the dorsal part of the rostral bank of the parieto-occipital sulcus and of the adjoining posterior part of the superior parietal lobule were studied by using different retrograde fluorescent tracers. Fluoro-Ruby, Fast blue and Diamidino yellow were injected into visual area V6A, and dorso-caudal (PMdc, F2) and dorso-rostral (PMdr, F7) premotor cortex, respectively. The parietal area of injection had been previously characterized physiologically in behaving monkeys, through a variety of oculomotor and visuomanual tasks. Area V6A is mainly linked by reciprocal projections to parietal areas 7m, MIP (medial intraparietal) and PEa, and, to a lesser extent, to frontal areas PMdr (rostral dorsal premotor cortex, F7) and PMdc (F2). All these areas project to that part of the dorsocaudal premotor cortex that has a direct access to primary motor cortex. V6A is also connected to area F5 and, to a lesser extent, to 7a, ventral (VIP) and lateral (LIP) intraparietal areas. This pattern of association connections may explain the presence of visually-related and eye-position signals in premotor cortex, as well as the influence of information concerning arm position and movement direction on V6A neural activity. Area V6A emerges as a potential 'early' node of the distributed network underlying visually-guided reaching. In this network, reciprocal association connections probably impose, through re-entrant signalling, a recursive property to the operations leading to the composition of eye and hand motor commands.     

Frontal eye field in prosimian galagos: Intracortical microstimulation and tracing studies

The frontal eye field (FEF) in prosimian primates was identified as a small cortical region, above and anterior to the anterior frontal sulcus, from which saccadic eye movements were evoked with electrical stimulation. Tracer injections revealed FEF connections with cortical and subcortical structures participating in higher order visual processing. Ipsilateral cortical connections were the densest with adjoining parts of the dorsal premotor and prefrontal cortex (PFC). Label in a region corresponding to supplementary eye field (SEF) of other primates, suggests the existence of SEF in galagos. Other connections were with ventral premotor cortex (PMV), the caudal half of posterior parietal cortex, cingulate cortex, visual areas within the superior temporal sulcus, and inferotemporal cortex. Callosal connections were mostly with the region of the FEF of another hemisphere, SEF, PFC, and PMV. Most subcortical connections were ipsilateral, but some were bilateral. Dense bilateral connections were to caudate nuclei. Densest reciprocal ipsilateral connections were with the paralamellar portion of mediodorsal nucleus, intralaminar nuclei and magnocellular portion of ventral anterior nucleus. Other FEF connections were with the claustrum, reticular nucleus, zona incerta, lateral posterior and medial pulvinar nuclei, nucleus limitans, pretectal area, nucleus of Darkschewitsch, mesencephalic and pontine reticular formation and pontine nuclei. Surprisingly, the superior colliculus (SC) contained only sparse anterograde label. Although most FEF connections in galagos are similar to those in monkeys, the FEF‐SC connections appear to be much less. This suggests that a major contribution of the FEF to visuomotor functions of SC emerged with the evolution of anthropoid primates.     

Subdivisions and connectional networks of the lateral prefrontal cortex in the macaque monkey

Neuroanatomical studies have long indicated that corticocortical connections are organized in networks that relate distinct sets of areas. Such networks have been emphasized by development of functional imaging methods for correlating activity across the cortex. Previously, two networks were recognized in the orbitomedial prefrontal cortex, the “orbital” and “medial” networks (OPFC and MPFC, respectively). In this study, three additional networks are proposed for the lateral prefrontal cortex: 1) a ventrolateral network (VLPFC) in and ventral to the principal sulcus; 2) a dorsal network (DPFC) in and dorsal to the principal sulcus and in the frontal pole; 3) a caudolateral network (CLPFC) in and rostral to the arcuate sulcus and the caudal principal sulcus. The connections of the first two networks are described here. Areas in each network are connected primarily with other areas in the same network, with overlaps around the principal sulcus. The VLPFC and DPFC are also connected with the OPFC and MPFC, respectively. Outside the prefrontal cortex, the VLPFC connects with specific areas related to somatic/visceral sensation and vision, in the frontoparietal operculum, insula, ventral bank/fundus of the superior temporal sulcus, inferior temporal gyrus, and inferior parietal cortex. In contrast, the DPFC connects with the rostral superior temporal gyrus, dorsal bank of the superior temporal sulcus, parahippocampal cortex, and posterior cingulate and retrosplenial cortex. Area 45a, in caudal VLPFC, is unique, having connections with all the networks. Its extrinsic connections resemble those of the DPFC. In addition, it has connections with both auditory belt/parabelt areas, and visual related areas. J. Comp. Neurol. 522:1641–1690, 2014. © 2013 Wiley Periodicals, Inc.     

Frontal eye field as defined by intracortical microstimulation in squirrel monkeys, owl monkeys, and macaque monkeys. II. Cortical connections

Physiological (intracortical microstimulation) and anatomical (transport of horseradish peroxidase conjugated to wheat germ agglutinin as shown by tetramethyl benzidine) approaches were combined in the same animals to reveal the locations, extents, and cortical connections of the frontal eye fields (FEF) in squirrel, owl, and macaque monkeys. In some of the same owl and macaque monkeys, intracortical microstimulation was also used to evoke eye movements from dorsomedial frontal cortex (the supplementary motor area). In addition, in all of the owl and squirrel monkeys, intracortical microstimulation was also used to evoke body movements from the premotor and motor cortex situated between the central dimple and the FEF. These microstimulation data were directly compared to the distribution of anterogradely and retrogradely transported label resulting from injections of tracer into the FEF in each monkey. Since the injection sites were limited to the physiologically defined FEF, the demonstrated connections were solely those of the FEF. To aid in the interpretation of areal patterns of connections, the relatively smooth cortex of owl and squirrel monkeys was unfolded, flattened, and cut parallel to the flattened surface. Cortex of macaque monkeys, which has numerous deep sulci, was cut coronally. Reciprocal connections with the ipsilateral frontal lobe were similar in all three species: dorsomedial cortex (supplementary motor area), cortex just rostral (periprincipal prefrontal cortex) to the FEF, and cortex just caudal (premotor cortex) to the FEF. In squirrel and owl monkeys, extensive reciprocal connections were made with cortex throughout the caudal half of the lateral fissure and, to a much lesser extent, cortex around the superior temporal sulcus. In macaque monkeys, only sparse connections were present with cortex of the lateral fissure, but extensive and dense connections were made with cortex throughout the caudal one-third to one-half of the superior temporal sulcus. In addition, very dense reciprocal connections were made with the cortex of the lateral, or inferior, bank of the intraparietal sulcus. Contralateral reciprocal connections in all three species were virtually limited to regions that correspond in location to the FEF and the supplementary motor area. The results of this study reveal connections between the physiologically defined frontal eye field and cortical regions known to participate in higher order visual processing, short-term memory, multimodal, visuomotor, and skeletomotor functions.(ABSTRACT TRUNCATED AT 400 WORDS)     

Pathways for motion analysis: cortical connections of the medial superior temporal and fundus of the superior temporal visual areas in the macaque

To identify the cortical connections of the medial superior temporal (MST) and fundus of the superior temporal (FST) visual areas in the extrastriate cortex of the macaque, we injected multiple tracers, both anterograde and retrograde, in each of seven macaques under physiological control. We found that, in addition to connections with each other, both MST and FST have widespread connections with visual and polysensory areas in posterior prestriate, parietal, temporal, and frontal cortex. In prestriate cortex, both areas have connections with area V3A. MST alone has connections with the far peripheral field representations of V1 and V2, the parieto-occipital (PO) visual area, and the dorsal prelunate area (DP), whereas FST alone has connections with area V4 and the dorsal portion of area V3. Within the caudal superior temporal sulcus, both areas have extensive connections with the middle temporal area (MT), MST alone has connections with area PP, and FST alone has connections with area V4t. In the rostral superior temporal sulcus, both areas have extensive connections with the superior temporal polysensory area (STP) in the upper bank of the sulcus and with area IPa in the sulcal floor. FST also has connections with the cortex in the lower bank of the sulcus, involving area TEa. In the parietal cortex, both the central field representation of MST and FST have connections with the ventral intraparietal (VIP) and lateral intraparietal (LIP) areas, whereas MST alone has connections with the inferior parietal gyrus. In the temporal cortex, the central field representation of MST as well as FST has connections with visual area TEO and cytoarchitectonic area TF. In the frontal cortex, both MST and FST have connections with the frontal eye field. On the basis of the laminar pattern of anterograde and retrograde label, it was possible to classify connections as forward, backward, or intermediate and thereby place visual areas into a cortical hierarchy. In general, MST and FST receive forward inputs from prestriate visual areas, have intermediate connections with parietal areas, and project forward to the frontal eye field and areas in the rostral superior temporal sulcus. Because of the strong inputs to MST and FST from area MT, an area known to play a role in the analysis of visual motion, and because MST and FST themselves have high proportions of directionally selective cells, they appear to be important stations in a cortical motion processing system.     

Ipsilateral cortical connections of dorsal and ventral premotor areas in New World owl monkeys

In order to compare connections of premotor cortical areas of New World monkeys with those of Old World macaque monkeys and prosimian galagos, we placed injections of fluorescent tracers and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in dorsal (PMD) and ventral (PMV) premotor areas of owl monkeys. Motor areas and injection sites were defined by patterns of movements electrically evoked from the cortex with microelectrodes. Labeled neurons and axon terminals were located in brain sections cut either in the coronal plane or parallel to the surface of flattened cortex, and they related to architectonically and electrophysiologically defined cortical areas. Both the PMV and PMD had connections with the primary motor cortex (M1), the supplementary motor area (SMA), cingulate motor areas, somatosensory areas S2 and PV, and the posterior parietal cortex. Only the PMV had connections with somatosensory areas 3a, 1, 2, PR, and PV. The PMD received inputs from more caudal portions of the cortex of the lateral sulcus and more medial portions of the posterior parietal cortex than the PMV. The PMD and PMV were only weakly interconnected. New World owl monkeys, Old World macaque monkeys, and galagos share a number of PMV and PMD connections, suggesting preservation of a common sensorimotor network from early primates. Comparisons of PMD and PMV connectivity with the cortex of the lateral sulcus and posterior parietal cortex of owl monkeys, galagos, and macaques help identify areas that could be homologous.     

Connections of the ventral granular frontal cortex of macaques with perisylvian premotor and somatosensory areas: anatomical evidence for somatic representation in primate frontal association cortex

In macaque monkeys with injections of tritiated amino acids or horseradish peroxidase in the ventrolateral granular frontal cortex, we observed extensive anterograde and retrograde labeling of the premotor and somatosensory cortex in and around the lateral sulcus. Comparable labeling was not present with large and small control injections of the dorsal granular cortex. Cytoarchitectonic evaluation of the perisylvian cortex in the three cases examined in detail indicated that labeled areas included the ventral premotor cortex (area 6V); the precentral opercular and orbitofrontal opercular areas (PrCO and OFO); the second somatosensory area (S-II); the opercular cortex immediately anterior to S-II, possibly corresponding to area 2 of the S-I complex; and the central part of the insular cortex, including portions of the granular and dysgranular insular fields (Ig, Idg). Labeling was particularly dense and extensive in areas 6V, S-II, and OFO. Lighter labeling was also present in the rostral inferior parietal lobule (areas 7b and POa). The distribution of label within perisylvian areas was not uniform: certain parts were heavily labeled, while other parts were lightly labeled or unlabeled. Comparison of label distribution with published accounts of the somatotopy of these areas indicates that forelimb and orofacial representations were selectively labeled. Further, our results, taken together with other recent anatomical findings (e.g., Matelli et al.: Journal of Comparative Neurology 251:281-298, 1987; Barbas and Pandya: Journal of Comparative Neurology 256:211-228, 1987) suggest strongly that there is a network of interconnected forelimb and orofacial representations in macaque cortex, involving the ventral granular frontal cortex, area 6V, OFO, opercular area 2, S-II, the central insula, and area 7b. Each injection of frontal cortex which labeled the perisylvian somatic cortex involved the cortex of the ventral rim of the principal sulcus (PSvr). The cortex surrounding the PSvr does not stand out as a distinct area in Nissl-stained material. However, examination of myelin-stained sections prepared from uninjected hemispheres with the Gallyas technique revealed the existence of a distinct zone centered on the PSvr. This myeloarchitectonic area, which we term area 46vr, is more heavily myelinated than the ventral bank and fundus of the principal sulcus (area 46v) but is less heavily myelinated than the ventral (inferior) convexity (area 12). Involvement of area 46vr in our injections was probably responsible for the strong labeling observed in perisylvian somatic areas.(ABSTRACT TRUNCATED AT 400 WORDS)     

Interhemispheric connections of the ventral premotor cortex in a new world primate

This study describes the pattern of interhemispheric connections of the ventral premotor cortex (PMv) distal forelimb representation (DFL) in squirrel monkeys. Our objectives were to describe qualitatively and quantitatively the connections of PMv with contralateral cortical areas. Intracortical microstimulation techniques (ICMS) guided the injection of the neuronal tract tracers biotinylated dextran amine or Fast blue into PMv DFL. We classified the interhemispheric connections of PMv into three groups. Major connections were found in the contralateral PMv and supplementary motor area (SMA). Intermediate interhemispheric connections were found in the rostral portion of the primary motor cortex, the frontal area immediately rostral and ventral to PMv (FR), cingulate motor areas (CMAs), and dorsal premotor cortex (PMd). Minor connections were found inconsistently across cases in the anterior operculum (AO), posterior operculum/inferior parietal cortex (PO/IP), and posterior parietal cortex (PP), areas that consistently show connections with PMv in the ipsilateral hemisphere. Within-case comparisons revealed that the percentage of PMv connections with contralateral SMA and PMd are higher than the percentage of PMv connections with these areas in the ipsilateral hemisphere; percentages of PMv connections with contralateral M1 rostral, FR, AO, and the primary somatosensory cortex are lower than percentages of PMv connections with these areas in the ipsilateral hemisphere. These studies increase our knowledge of the pattern of interhemispheric connection of PMv. They help to provide an anatomical foundation for understanding PMv's role in motor control of the hand and interhemispheric interactions that may underlie the coordination of bimanual movements.     

Striatal connections of the parietal association cortices in rhesus monkeys

The corticostriatal connections of the parietal association cortices were examined by the autoradiographic technique in rhesus monkeys. The results show that the rostral portion of the superior parietal lobule projects predominantly to the dorsal portion of the putamen, whereas the caudal portion of the superior parietal lobule and the cortex of the upper bank of the intraparietal sulcus have connections with the caudate nucleus as well as with the dorsal portion of the putamen. The medial parietal convexity cortex projects strongly to the caudate nucleus, and has less extensive projections to the putamen. In contrast, the medial parietal cortex within the caudal portion of the cingulate sulcus projects predominantly to the dorsal portion of the putamen, and has only minor connections with the caudate nucleus. The rostral portion of the inferior parietal lobule projects mainly to the ventral sector of the putamen, and has only minor connections with the caudate nucleus. The middle portion of the inferior parietal lobule has sizable projections to both the putamen and the caudate nucleus. The caudal portion of the inferior parietal lobule as well as the lower bank of the intraparietal sulcus project predominantly to the caudate nucleus, and have relatively minor connections with the putamen. The cortex of the parietal opercular region also shows a specific pattern of corticostriatal projections. Whereas the rostral portion projects exclusively to the ventral sector of the putamen, the caudal portion has connections to the caudate nucleus as well. Thus, it seems that parietostriatal projections show a differential topographic distribution; within both the superior and the inferior parietal region, as one progresses from rostral to caudal, there is a corresponding shift in the predominance of projections from the putamen to the caudate nucleus. In addition, with regard to the projections to the putamen, the superior parietal lobule is related mainly to the dorsal portion, and the inferior parietal lobule to the ventral portion. The striatal projections of the cortex of the caudal portion of the cingulate gyrus (corresponding in part to the supplementary sensory area) and of the rostral parietal opercular region (corresponding in part to the second somatosensory area) are directed almost exclusively to the dorsal and ventral sectors of the putamen, respectively. This pattern resembles that of the primary somatosensory cortex. The results are discussed with regard to the overall architectonic organization of the posterior parietal region. Possible functional aspects of parietostriatal connectivity are considered in the light of physiological and behavioral studies. © 1993 Wiley-Liss, Inc.     

Distribution of cat-301 immunoreactivity in the frontal and parietal lobes of the macaque monkey

The distribution of the monoclonal antibody Cat-301 was examined in the frontal and parietal cortex of macaque monkeys. In both regions the distribution was uniform within cytoarchitecturally defined areas (or subareas) but varied between them. In all areas, Cat-301 labeled the soma and proximal dendrites of a restricted population of neurons. In the frontal lobe, Cat-301-positive neurons were intensely immunoreactive and present in large numbers in the motor cortex (area 4), premotor cortex (area 6, excluding its lower ventral part), the supplementary motor area (SMA), and the caudal prefrontal cortex (areas 8a, 8b and 45). In the parietal lobe, large numbers of intensely immunoreactive neurons were evident in the post-central gyrus (areas 1 and 2), the superior parietal lobule (PE/5), and the dorsal bank (PEa), fundus (IPd), and deep half of the ventral bank (POa(i] of the intraparietal sulcus (IPS). Two major patterns of laminar distribution were evident. In motor, supplementary motor, premotor (excluding the lower part of its ventral division), and the caudal prefrontal cortex (Walker's areas 8a, 8b and 45), and throughout the parietal cortex (with the exception of area 3), Cat-301-positive neurons were concentrated in the lower part of layer III and in layer V. The laminar positions of labeled cells in these areas were remarkably constant, as were the proportions of labeled neurons that had pyramidal and nonpyramidal morphologies (means of 30.2% and 69.8%, respectively). In contrast, in prefrontal areas 9, 10, 11, 12, 13, 14, and 46, in the cingulate cortex (areas 23, 24 and 25), and in the lower part of the ventral premotor cortex, Cat-301-positive neurons were spread diffusely across layers II to VI and a mean of 3.6% of the labeled neurons were pyramidal while 96.4% were nonpyramidal. Area 3 was unique among frontal and parietal areas, in that the labeled neurons in this area were concentrated in layers IV and VI. The areas in the frontal lobe which were heavily labeled are thought to be involved in the control of somatic (areas 4 and 6) and ocular (areas 8 and 45) movements. Those in parietal cortex may be classified as areas with somatosensory functions (1, 2, PE/5, and PEa) and areas which may participate in the analysis of visual motion (Pandya and Seltzer's IPd and POa(i), which contain Maunsell and Van Essen's VIP). The parietal somatosensory areas are connected to frontal areas with somatic motor functions, while POa(i) is interconnected with the frontal eye fields (8a and 45).(ABSTRACT TRUNCATED AT 250 WORDS)     

Corticocortical connections between frontal periarcuate regions and visual areas of the superior temporal sulcus and the adjoining inferior parietal lobule in the macaque monkey

In macaque monkeys, corticocortical connections between distinct parietotemporal visual areas (areas MST–FST, DP, and 7a) and frontal periarcuate areas are studied using tritiated aminoacids and WGA-HRP. While labeling within the banks of the principal sulcus, the dorsal part of the arcuate concavity, and the banks of the upper arcuate limb were present in both 7a and MST–FST injected animals; in the latter cases, additional projections were found towards frontal regions including the dorsomedial frontal cortex and the posterior bank of the arcuate ventral limb. Our results point to widespread frontal connections of the MST–FST complex, involving both prefrontal and premotor cortical regions.     

Organization of the posterior parietal cortex in galagos: II. Ipsilateral cortical connections of physiologically identified zones within anterior sensorimotor region

We studied cortical connections of functionally distinct movement zones of the posterior parietal cortex (PPC) in galagos identified by intracortical microstimulation with long stimulus trains (～500 msec). All these zones were in the anterior half of PPC, and each of them had a different pattern of connections with premotor (PM) and motor (M1) areas of the frontal lobe and with other areas of parietal and occipital cortex. The most rostral PPC zone has major connections with motor and visuomotor areas of frontal cortex as well as with somatosensory areas 3a and 1‐2 and higher order somatosensory areas in the lateral sulcus. The dorsal part of anterior PPC region representing hand‐to‐mouth movements is connected mostly to the forelimb representation in PM, M1, 3a, 1‐2, and somatosensory areas in the lateral sulcus and on the medial wall. The more posterior defensive and reaching zones have additional connections with nonprimary visual areas (V2, V3, DL, DM, MST). Ventral aggressive and defensive face zones have reciprocal connections with each other as well as connections with mostly face, but also forelimb representations of premotor areas and M1 as well as prefrontal cortex, FEF, and somatosensory areas in the lateral sulcus and areas on the medial surface of the hemisphere. Whereas the defensive face zone is additionally connected to nonprimary visual cortical areas, the aggressive face zone is not. These differences in connections are consistent with our functional parcellation of PPC based on intracortical long‐train microstimulation, and they identify parts of cortical networks that mediate different motor behaviors. J. Comp. Neurol. 517:783–807, 2009. © 2009 Wiley‐Liss, Inc.     

Cortical connections of the caudal subdivision of the dorsolateral area (V4) in monkeys.

Evidence suggests that all primates have rostral and caudal subdivisions in the region of visual cortex identified as the dorsolateral area (DL) or V4. However, the connections of DL/V4 have not been examined in terms of these subdivisions. To determine the cortical connections of the caudal subdivision of DL (DLC) in squirrel monkeys, injections of the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase, Diamidino Yellow, and Fluoro-Gold were made in cortex rostral to V II. To aid in delineating the borders of DLC, cortex was also evaluated architectonically. Based on similar patterns of connections, DLC extends from dorsolateral to ventrolateral cortex. DLC receives strong, feedforward input from V II and projects in a feedforward fashion to the rostral subdivision of DL (DLR) and caudal inferior temporal (IT) cortex, including a separate location in the inferior temporal sulcus. DLC has weaker connections with V I, the middle temporal area (MT), cortex rostral to MT in the location of the fundal superior temporal area (FST), cortex dorsal to DLC, ventral cortex rostral to V II, and cortex in the frontal lobe, lateral to the inferior arcuate sulcus. Only lateral DLC has connections with V I, and only dorsolateral DLC has connections with cortex dorsal to DLC. The topographic organization of DLC was inferred from its connections with V II. Thus, dorsolateral DLC represents the lower field, lateral DLC represents central vision, and ventrolateral DLC represents the upper field. Limited observations were made on DLR. Confirming earlier observations (Cusick and Kaas: Visual Neurosci. 1:211, 1988), DLR is paler than DLC myeloarchitectonically. DLR receives only sparse feedforward input from V II, but stronger input from DLC. DLR has strong connections with cortex just rostral to dorsal V II, ventral posterior parietal cortex in the sylvian fissure, MT, the medial superior temporal area, FST, and the inferior temporal sulcus. DLR also shares connections with IT cortex. Thus, while both DLC and DLR are involved in the pathway relaying visual information to IT cortex, an area specialized for object vision, DLR also projects densely to areas such as MT involved in the pathway relaying to posterior parietal cortex, a region specialized for spatial localization and motion perception.     

Corpus callosum connections of subdivisions of motor and premotor cortex, and frontal eye field in a prosimian primate, Otolemur garnetti

The callosal connections of motor and premotor fields in the frontal cortex of galagos were examined by placing multiple tracers into the primary motor area (M1), dorsal premotor area (PMD), ventral premotor area (PMV), supplementary motor area (SMA), and frontal eye field (FEF) following intracortical microstimulation. Retrogradely labeled neurons in the opposite hemisphere were plotted and superimposed onto brain sections stained with myelin and cytochrome oxidase for architectonic analysis. The main callosal connections of M1 and the caudal portion of PMD (PMDc) were with homotopic sites, and the major callosal connections of the rostral portion of PMD (PMDr), SMA, and FEF were with homotopic sites and adjoining cortex in the frontal lobe. In addition, M1 forelimb representation had sparse callosal connections, whereas M1 trunk and face representations, as well as the premotor areas, had dense callosal connections. The sparse interhemispheric connections of the forelimb sector of M1 suggests that the control of each forelimb is largely from the contralateral M1 in galagos, as in other primates.     

Corticocortical projections to area 1 in squirrel monkeys (Saimiri sciureus)

Cortical area 1 is a non‐primary somatosensory area in the primate anterior parietal cortex that is critical to tactile discrimination. The corticocortical projections to area 1 in squirrel monkeys were determined by placing multiple injections of anatomical tracers into separate body part representations defined by multiunit microelectrode mapping in area 1. The pattern of labeled cells in the cortex indicated that area 1 has strong intrinsic connections within each body part representation and has inputs from somatotopically matched regions of areas 3b, 3a, 2 and 5. Somatosensory areas in the lateral sulcus, including the second somatosensory area (S2), the parietal ventral area (PV), and the presumptive parietal rostral (PR) and ventral somatosensory (VS) areas, also project to area 1. Topographically organized projections to area 1 also came from the primary motor cortex (M1), the dorsal and ventral premotor areas (PMd and PMv), and the supplementary motor area (SMA). Labeled cells were also found in cingulate motor and sensory areas on the medial wall of the hemisphere. Previous studies revealed a similar pattern of projections to area 1 in Old World macaque monkeys, suggesting a pattern of cortical inputs to area 1 that is common across anthropoid primates.     

Cortical connections of the frontoparietal opercular areas in the Rhesus monkey

The connections of the frontoparietal opercular areas were studied in rhesus monkeys by using antero- and retrograde tracer techniques. The rostral opercular cortex including the gustatory and proisocortical motor (ProM) areas is connected with precentral areas 3, 1, and 2 as well as with the rostral portion of the opercular area which resembles the second somatosensory type of cortex (area SII) and the ventral portion of area 6. Its distant connections are with the ventral portion of prefrontal areas 46, 11, 12, and 13 as well as with the rostral insula and cingulate motor area (CMAr). The mid opercular region (areas 1 and 2) is connected with pre- and postcentral areas 3, 1, and 2 as well as SII. Additionally, it is connected with the ventral portion of area 6, area 44, area ProM, the gustatory area, and the rostral insula. Its distant connections are with area 4, the ventral portion of area 46, area 7b, and area POa in the intraparietal sulcus (IPS). The rostral parietal opercular region is connected with the postcentral portions of areas 3, 1, and 2; areas 5, 7, and SII; the gustatory area; and the vestibular area. Its other connections are with area 4, area 44, the ventral portion of area 46, area ProM, CMAr, and the supplementary motor area (SMA). The caudal opercular region is connected with the dorsal portion of area 3; areas 2, 5, and 7a; and areas PEa as well as IPd of IPS. It is also connected with area SII, insula, and the superior temporal sulcus. Its distant connections are with area 44; the dorsal portion of area 8 and the ventral portion of area 46; as well as CMAr, SMA, and the supplementary sensory area. This connectivity suggests that the ventral somatosensory areas are involved in sensorimotor activities mainly related to head, neck, and face structures as well as to taste. Additionally, these areas may have a role in frontal (working) and temporal (tactile) memory systems. J. Comp. Neurol. 403:431–458, 1999. © 1999 Wiley-Liss, Inc.