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.     

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)     

Architectionis,somatotopic organization,and ipsilateral cortical connections of the primary motor area (M1) of owl monkeys

The ipsilateral cortical connections of primary motor cortex (M1) of owl monkeys were revealed by injecting WGA-HRP and fluorescent tracers into M1 sites identified by intracortical microstimulation. In some of the same animals, the extent and somatotopic organization of M1 was determined by making detailed microstimulation movement maps and relating the results to cortical architectonics. Thus, delineation of M1 was based on a combination of physiological and anatomical characteristics. M1 comprised most, but not all, of the cortex rostral to area 3a where movements were evoked at low levels of current (40 μA or less). Analysis of somatotopic patterns and architectonics placed some of the low-threshold sites in a ventral premotor field (PMV) and the dorsomedially situated supplementary motor area (SMA). Movements were also reliably elicited from a dorsal premotor area (PMD) at higher currents. M1 was characterized by a somatotopic global organization, representing hindlimb, trunk, forelimb, and face movements in a mediolateral sequence, and a mosaic local organization, with a given movement typically represented at several different sites. Architectionically, M1 was characterized by the absence of a granular layer IV and the presence of very large layer V pyramidal cells. However, M1 was not uniform in structure: pyramidal cells were larger caudally than rostrally, a feature we used to distinguish caudal (M1c) and rostral (M1r) subdivisions of the area. M1 resembles Brodmann's area 4, although the rostral subdivision has probably been considered as part of area 6 by some workers. Tracer injections of M1 revealed somatotopically distributed connections with motor areas PMD, PMV, and SMA, as well as in somatosensory areas 3a, 1, 2, and S2. Weaker connections were with area 3b, posterior parietal cortex, the parietal ventral area (PV), and cingulate cortex. M1r and M1c differed connectionally as well as architectonically, M1c being connected primarily with somatosensory areas, while M1r was strongly connected with both non-primary motor cortex and somatosensory cortex. These results indicate that M1 interacts directly with at least three non-primary motor areas and at least six somatosensory areas.     

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

The present study describes the pattern of connections of the ventral premotor cortex (PMv) with various cortical regions of the ipsilateral hemisphere in adult squirrel monkeys. Particularly, we 1) quantified the proportion of inputs and outputs that the PMv distal forelimb representation shares with other areas in the ipsilateral cortex and 2) defined the pattern of PMv connections with respect to the location of the distal forelimb representation in primary motor cortex (M1), primary somatosensory cortex (S1), and supplementary motor area (SMA). Intracortical microstimulation techniques (ICMS) were used in four experimentally naïve monkeys to identify M1, PMv, and SMA forelimb movement representations. Multiunit recording techniques and myelin staining were used to identify the S1 hand representation. Then, biotinylated dextran amine (BDA; 10,000 MW) was injected in the center of the PMv distal forelimb representation. After tangential sectioning, the distribution of BDA‐labeled cell bodies and terminal boutons was documented. In M1, labeling followed a rostrolateral pattern, largely leaving the caudomedial M1 unlabeled. Quantification of somata and terminals showed that two areas share major connections with PMv: M1 and frontal areas immediately rostral to PMv, designated as frontal rostral area (FR). Connections with this latter region have not been described previously. Moderate connections were found with PMd, SMA, anterior operculum, and posterior operculum/inferior parietal area. Minor connections were found with diverse areas of the precentral and parietal cortex, including S1. No statistical difference between the proportions of inputs and outputs for any location was observed, supporting the reciprocity of PMv intracortical connections. J. Comp. Neurol. 495:374–390, 2006. © 2006 Wiley‐Liss, Inc.     

Corticocortical projections to representations of the teeth,tongue, and face in somatosensory area 3b of macaques

We placed injections of anatomical tracers into representations of the tongue, teeth, and face in the primary somatosensory cortex (area 3b) of macaque monkeys. Our injections revealed strong projections to representations of the tongue and teeth from other parts of the oral cavity responsive region in 3b. The 3b face also provided input to the representations of the intraoral structures. The primary representation of the face showed a pattern of intrinsic connections similar to that of the mouth. The area 3b hand representation provided little to no input to either the mouth or the face representations. The mouth and face representations of area 3b received projections from the presumptive oral cavity and face regions of other somatosensory areas in the anterior parietal cortex and the lateral sulcus, including areas 3a, 1, 2, the second somatosensory area (S2), the parietal ventral area (PV), and cortex that may include the parietal rostral (PR) and ventral somatosensory (VS) areas. Additional inputs came from primary motor (M1) and ventral premotor (PMv) areas. This areal pattern of projections is similar to the well‐studied pattern revealed by tracer injections in regions of 3b representing the hand. The tongue representation appeared to be unique in area 3b in that it also received inputs from areas in the anterior upper bank of the lateral sulcus and anterior insula that may include the primary gustatory area (area G) and other cortical taste‐processing areas, as well as a region of lateral prefrontal cortex (LPFC) lining the principal sulcus. J. Comp. Neurol. 522:546–572, 2014. © 2013 Wiley Periodicals, Inc.     

A quantitative study of the distribution of neurons projecting to the precentral motor cortex in the monkey (M. fascicularis)

The relative numbers and locations of neurons projecting to the "forelimb" region of the precentral motor cortex were studied in three monkeys by using the retrograde transport of horseradish peroxidase. Within the forelimb area of the motor cortex itself, there are extensive and profuse interconnections. However, regions within this area receive afferents from very few neurons in other parts of the motor cortex representing hindlimb or head movements. Most of the motor cortical representation of the forelimb in the anterior bank of the central sulcus is devoid of callosal connections. In both the ipsilateral and contralateral hemispheres, the premotor (lateral area 6) and supplementary motor (medial area 6) areas dominate quantitatively the inputs to the motor cortical representation of the forelimb. The afferents from the premotor area are restricted and come from a region immediately behind the arcuate spur and adjacent parts of the superior and inferior limbs of the arcuate sulcus in the floor, caudal bank, and caudal lip of that sulcus. From the supplementary motor area (SMA), afferents originate from its whole rostrocaudal extent. Thalamic nuclear regions projecting to a restricted zone in the anterior bank of the central sulcus are recipients of cerebellar and somatosensory outputs. Involvement of more anterior parts of the motor cortex by the tracer labels thalamocortical cells, which are targets of pallidal output also. Within the first somatosensory cortex, cytoarchitectonic areas 1, 2, and 3a project to area 4. The projection from area 3a may provide one pathway by which short-latency peripheral inputs, especially from muscles, reach the motor cortex.     

High‐order motor cortex in rats receives somatosensory inputs from the primary motor cortex via cortico‐cortical pathways

The motor cortex of rats contains two forelimb motor areas; the caudal forelimb area (CFA) and the rostral forelimb area (RFA). Although the RFA is thought to correspond to the premotor and/or supplementary motor cortices of primates, which are higher‐order motor areas that receive somatosensory inputs, it is unknown whether the RFA of rats receives somatosensory inputs in the same manner. To investigate this issue, voltage‐sensitive dye (VSD) imaging was used to assess the motor cortex in rats following a brief electrical stimulation of the forelimb. This procedure was followed by intracortical microstimulation (ICMS) mapping to identify the motor representations in the imaged cortex. The combined use of VSD imaging and ICMS revealed that both the CFA and RFA received excitatory synaptic inputs after forelimb stimulation. Further evaluation of the sensory input pathway to the RFA revealed that the forelimb‐evoked RFA response was abolished either by the pharmacological inactivation of the CFA or a cortical transection between the CFA and RFA. These results suggest that forelimb‐related sensory inputs would be transmitted to the RFA from the CFA via the cortico‐cortical pathway. Thus, the present findings imply that sensory information processed in the RFA may be used for the generation of coordinated forelimb movements, which would be similar to the function of the higher‐order motor cortex in primates.     

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.     

Movement representation in the dorsal and ventral premotor areas of owl monkeys: A microstimulation study

We used intracortical microstimulation to investigate the lateral premotor cortex and neighboring areas in 14 hemispheres of owl monkeys, focusing on the somatotopic distribution of evoked movements, thresholds for forelimb movements, and the relative representation of proximal and distal forelimb movements. We elicited movements from the dorsal and ventral premotor areas (PMD, PMV), the caudal and rostral divisions of primary motor cortex (Mlc, Mlr), the frontal eye field (FEF), the dorsal oculomotor area (OMD; area 8b), the supplementary motor area (SMA), and somatosensory cortex (areas 3a and 3b). Area PMD was composed of architectonically distinguishable caudal and rostral subdivisions (PMDc, PMDr). Stimulation of PMD elicited movements of the hindlimb, forelimb, neck and upper trunk, face, and eyes. Hindlimb and forelimb movements were represented in the caudalmost part of PMDc. Face, neck, and eye movements were represented in the lateral and rostral parts of PMDc and in PMDr. Stimulation of PMV elicited forelimb and orofacial movements, but not hindlimb movements. Both proximal and distal forelimb movements were elicited from PMDc and PMV, although PMD stimulation elicited mainly shoulder and elbow movements, while PMV stimulation evoked primarily wrist and digit movements. Distal movements were evoked more frequently from PMV than from Mlr or Mlc. Across cases, the median forelimb thresholds for PMDc and PMV were 60 and 36 μA, respectively, values that differ significantly from each other and from the value of 11 μA obtained for Mlr. Our observations indicate that premotor cortex is much more responsive to electrical stimulation than commonly thought, and contains a large territory from which eye movements can be elicited. These results suggest that in humans, much of the electrically excitable cortex located on the precentral gyrus, including cortex sometimes considered part of the frontal eye field, is probably homologous to the premotor cortex of nonhuman primates. © 1996 Wiley-Liss, Inc.     

Cortical and thalamic connections of the parietal ventral somatosensory area in marmoset monkeys (Callithrix jacchus).

Microelectrode mapping methods were used to define the parietal ventral somatosensory area (PV) on the upper bank of the lateral sulcus in five marmosets (Callithrix jacchus). In the same animals, neuroanatomical tracers were placed into electrophysiologically identified sites in PV and/or the second somatosensory area (S2). Foci of anterograde and retrograde label were related to electrophysiological maps of cortical areas and cortical and thalamic architecture. The results lead to the following conclusions: (1) Multiunit recordings from cortex on the upper bank of the lateral sulcus demonstrate that PV is somatotopically organized, with the face representation adjoining area 3b and the hindlimb and tail representations away from this border in cortex deep on the upper bank of the lateral sulcus. The forelimb representation is caudal in PV adjacent to the S2 forelimb representation. The body surface representation in PV approximates a mirror image of that in S2; (2) Areas PV and S2 are less myelinated and have less cytochrome oxidase enzyme activity than area 3b; (3) The ventroposterior inferior nucleus (VPI) of the thalamus provides the major somatosensory projections to PV. PV is reciprocally connected with VPI and anterior pulvinar; (4) PV has ipsilateral cortical connections with areas 3a, 3b, 1, and M1 and higher order somatosensory fields, and at least most of these connections are somatotopically matched; and (5) Callosal connections of PV are with S2 and PV of the other cerebral hemisphere. These results further establish PV as one of at least four somatosensory areas of the lateral sulcus of primates.     

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.     

A chronic unit study of the sensory properties of neurons in the forelimb areas of rat sensorimotor cortex

The sensory properties of neurons in the several forelimb areas of rat sensorimotor cortex were examined using the technique of extracellular single-unit recording in the awake, head-restrained rat. Cells with peripheral receptive fields were tested for the amount and modality of sensory input during joint manipulation and brushing and tapping of limbs, face and trunk. Input-output correlations were made on the basis of the results of receptive field mapping and intracortical microstimulation in the same electrode penetration. It was found that neurons (n = 117) in the rostral forelimb area receive virtually no sensory input while 30% of neurons (n = 114) in the caudal forelimb primary motor area do receive such input. The inputs to caudal forelimb motor area neurons were primarily (83%) from single joints; along perpendicular electrode penetrations the same joint that activated a cortical cell also moved when microstimulation was delivered along the same electrode penetration. In the granular and dysgranular zones of somatic sensory forelimb cortex, 70% of neurons (n = 82) were responsive to peripheral sensory inputs, with most of the cells in the granular cortex responsive to cutaneous inputs while cells in the dysgranular cortex were more responsive to deep inputs. The lack of sensory inputs to the rostral forelimb motor area is consistent with the proposal that this region may be a part of the supplementary motor area of the rat.     

Topography,architecture, and connections of somatosensory cortex in opossums: Evidence for five somatosensory areas

Microelectrode maps of somatosensory inputs were related to cortical architecture and patterns of cortical connections to provide evidence for five subdivisions of the somatosensory or sensorimotor cortex in North American opossums (Didelphis marsupialis). Microelectrode recordings revealed three systematic representations of the body surface. A large mediolaterally oriented representation was identified as the primary somatosensory area (S1) by its relative position, somatotopy, architecture, and connections. S1 represented the hindlimb, trunk, forelimb, and face in a mediolateral sequence. Two additional representations of cutaneous receptors were found caudolateral to S1, each with face representations adjacent to the border of lateral S1 and other body-part representations progressing more caudally toward the auditory cortex. We identified the more dorsal field as the second somatosensory area (S2) and the more ventral field as the parietal ventral area (PV). Tracers injected into S1 labeled neurons and terminals in architectonically distinct fields rostral and caudal to S1, the somatosensory caudal area (SC) and the somatosensory rostral area (SR). Movements could be evoked by microstimulation from sites scattered over S1, SR, and the frontal cortex, but thresholds were high and uncharacteristic of motor cortex. S2 and PV merged caudally with the cortex responsive to auditory stimuli, possibly A1, and neurons in some caudal recording sites in PV were activated by both auditory and cutaneous stimuli. Primary (V1) and secondary (V2) visual areas were also identified by microelectrode mapping, architecture, and connections. In addition, at least part of the cortex between V2 and the somatosensory cortex had visual connections. Thus, most of the dorsolateral cortex of opossums appears to be somatosensory, auditory, or visual. © 1996 Wiley-Liss, Inc.     

Microstimulation and architectonics of frontoparietal cortex in common marmosets (Callithrix jacchus)

We investigated the organization of frontoparietal cortex in the common marmoset (Callithrix jacchus) by using intracortical microstimulation and an architectonic analysis. Primary motor cortex (M1) was identified as an area that evoked visible movements at low levels of electric current and had a full body representation of the contralateral musculature. Primary motor cortex represented the contralateral body from hindlimb to face in a mediolateral sequence, with individual movements such as jaw and wrist represented in multiple nearby locations. Primary motor cortex was coextensive with an agranular area of cortex marked by a distinct layer V of large pyramidal cells that gradually decreased in size toward the rostral portion of the area and was more homogenous in appearance than other New World primates. In addition to M1, stimulation also evoked movements from several other areas of frontoparietal cortex. Caudal to primary motor cortex, area 3a was identified as a thin strip of cortex where movements could be evoked at thresholds similar to those in M1. Rostral to primary motor cortex, supplementary motor cortex and premotor areas responded to higher stimulation currents and had smaller layer V pyramidal cells. Other areas evoking movements included primary somatosensory cortex (area 3b), two lateral somatosensory areas (areas PV and S2), and a caudal somatosensory area. Our results suggest that frontoparietal cortex in marmosets is organized in a similar fashion to that of other New World primates.     

Anatomical and physiological definition of the motor cortex of the marmoset monkey

We used a combination of anatomical and physiological techniques to define the primary motor cortex (M1) of the marmoset monkey and its relationship to adjacent cortical fields. Area M1, defined as a region containing a representation of the entire body and showing the highest excitability to intracortical microstimulation, is architecturally heterogeneous: it encompasses both the caudal part of the densely myelinated "gigantopyramidal" cortex (field 4) and a lateral region, corresponding to the face representation, which is less myelinated and has smaller layer 5 pyramidal cells (field 4c). Rostral to M1 is a field that is strongly reminiscent of field 4 in terms of cyto- and myeloarchitecture but that in the marmoset is poorly responsive to microstimulation. Anatomical tracing experiments revealed that this rostral field is interconnected with visual areas of the posterior parietal cortex, whereas M1 itself has no such connections. For these reasons, we considered this field to be best described as part of the dorsal premotor cortex and adopted the designation 6Dc. Histological criteria were used to define other fields adjacent to M1, including medial and ventral subdivisions of the premotor cortex (fields 6M and 6V) and the rostral somatosensory field (area 3a), as well as a rostral subdivision of the dorsal premotor area (field 6Dr). These results suggest a basic plan underlying the histological organization of the caudal frontal cortex in different simian species, which has been elaborated during the evolution of larger species of primate by creation of further morphological and functional subdivisions.     

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.     

Thalamocortical and corticothalamic connections of multiple functional domains in posterior parietal cortex of galagos

In prosimian galagos, the posterior parietal cortex (PPC) is subdivided into a number of functional domains where long-train intracortical microstimulation evoked different types of complex movements. Here, we placed anatomical tracers in multiple locations of PPC to reveal the origins and targets of thalamic connections of four PPC domains for different types of hindlimb, forelimb, or face movements. Thalamic connections of all four domains included nuclei of the motor thalamus, ventral anterior and ventral lateral nuclei, as well as parts of the sensory thalamus, the anterior pulvinar, posterior and ventral posterior superior nuclei, consistent with the sensorimotor functions of PPC domains. PPC domains also projected to the thalamic reticular nucleus in a somatotopic pattern. Quantitative differences in the distributions of labeled neurons in thalamic nuclei suggested that connectional patterns of these domains differed from each other.     

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.     

Intact intracortical microstimulation (ICMS) representations of rostral and caudal forelimb areas in rats with quinolinic acid lesions of the medial or lateral caudate-putamen in an animal model of Huntington's disease

Neurotoxic, cell-specific lesions of the rat caudate-putamen (CPu) have been proposed as a model of human Huntington's disease and as such impair performance on many motor tasks, including skilled forelimbs tasks such as reaching for food. Because the CPu and motor cortex share reciprocal connections, it has been proposed that the motor deficits are due in part to a secondary disruption of motor cortex. The purpose of the present study was to examine the functionality of the motor cortex using intracortical microstimulation (ICMS) following neurotoxic lesions of the CPu. ICMS maps have been shown to be sensitive indicators of motor skill, cortical injury, learning, and experience. Long-evans hooded rats received a sham, a medial, or a lateral CPu lesion using the neurotoxin, quinolinic acid (2,3-pyridinedicarboxylic acid). Two weeks later the motor cortex was stimulated under light ketamine anesthesia. Neither lateral nor medial lesions of the CPu altered the stimulation threshold for eliciting forelimb movements, the type of movements elicited, or the size of the rostral forelimb (RFA) and caudal forelimb areas (CFA) from which movements were elicited. The preservation of ICMS forelimb movement representations (the forelimb map) in rats with cell-specific CPu lesions suggests motor impairments following lesions of the lateral striatum are not due to the disruption of the motor map. Therefore, the impairments that follow striatal cell loss are due either to alterations in circuitry that is independent of motor cortex or to alterations in circuitry afferent to the motor cortex projections.     

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.