Connections of area 2 of somatosensory cortex with the anterior pulvinar and subdivisions of the ventroposterior complex in macaque monkeys

The principal goal of the present study was to determine the thalamic connections of area 2 of postcentral somatosensory cortex of monkeys. The placement of injections of anatomical tracers (horseradish peroxidase, wheat germ agglutinin, or ³H-proline) was guided by extensive microelectrode maps of cortex in the region of the injection site. These maps identified the body parts represented in the cortex included in the injection site, and provided information about the physiological boundaries of area 2, which was related later to the cortical architecture. Most injections were placed in the representation of the hand in area 2, which was highly responsive to cutaneous stimuli and could be mapped in detail. Injections were also placed in other parts of area 2, area 1, or area 5, and some injections involved more than one area. As other investigators have determined, regions of retrograde and anterograde thalamic label overlapped, demonstrating that connections with cortex are reciprocal. Injections completely confined to area 2 consistently produced label in two locations: the anterior pulvinar (Pa) and a dorsal capping zone of the ventroposterior complex that we term the ventroposterior superior nucleus (VPS). Single restricted injection sites resulted in one region of label in VPS, and multiple foci of label in Pa. In some cases where the injection was confined to the representation of the hand in area 2, label was also found more ventrally in the ventroposterior complex in ventroposterior nucleus proper (VP). Thus, area 2 receives input from Pa, VPS, and, at least in some locations and individuals, VP. Injections of tracers into area 1 confirmed previous findings that area 1 is densely interconnected with VP. In addition, there appear to be sparse connections with VPS. There was no evidence of connections with Pa. Evidence from injection sites that extended from area 2 into areas 5 and 7, and from injection sites in area 5, indicates that the lateral posterior nucleus (LP) projects to rostral areas 5 and 7. The results support the conclusion that area 2 is a functionally distinct subdivision of somatosensory cortex, and indicate that area 2 has thalamic connections that are characteristic of both “sensory” (VP and VPS) and “association” (Pa) cortical fields.     

Neurochemical subdivisions of the inferior pulvinar in macaque monkeys

The architecture of the pulvinar of rhesus monkeys was investigated by acetylcholinester ase (AChE) histochemistry, and by immunocytochemiatry for calbindin-D_28k and the SMI-32 antibody. The presence of four inferior subdivisions, comparable to those found in architectonic connectional studies in squirrel monkeys (C. G. Cusick, J Scripter, J. G. Darensbourg, and J. T. Weber, 1993, J. Comp. Neurol. 336:1–30), provided a basis for a proposed revised terminology for visual sectors of the macaque pulvinar. In the present study, the inferior pulvinar (PI) was identified as a neurochemically distinct region that included the traditional cytoarchitectonic nucleus PI and adjacent portions of the lateral and medial pulvmar nuclei, PL and PM. In calbindin-D_28k stains, the lateral. subdivision of the inferior pulvinar (PI_L) had less intense neuropil staining than the adjacent central division, PI_c. The PI_L was characterized by large, intensely immunopositive neurons seldom found within Pl_c. PI_L occupied the traditional PL and PI and exhibited a shell zone, PI_L-S, restricted to PL. The medial division of the inferior pulvinar (PI_M) was in a location previously shown to be strongly connected with the middle temporal visual area (MT) in macaques. PI_M was found in the medial one-half of the traditional PI and extended into adjacent portions of the traditional PM and PL. PI_M was distinguished by less intense staining for calbindin and many cells stained with the SMI-32 antibody for neurofilament protein. In AChE stains, PI_L was moderately dark, Pl_c appeared lighter, and PI_M was characterized by small, intensely stained patches. The small posterior division (PI_P) stained darkly for calbindin, lightly for AChE, and was unstained with the SMI-32 antibody. Thus, neurochemical, and perhaps connectional, subdivisions exist within PI, the region of the pulvinar that relays information to striate, “lower order” extrastriate, and inferotemporal visual cortex. © 1995 Wiley-Liss, Inc.     

Cortical connections to single digit representations in area 3b of somatosensory cortex in squirrel monkeys and prosimian galagos

The ventral posterior nucleus of thalamus sends highly segregated inputs into each digit representation in area 3b of primary somatosensory cortex. However, the spatial organization of the connections that link digit representations of areas 3b with other somatosensory areas is less understood. Here we examined the cortical inputs to individual digit representations of area 3b in four squirrel monkeys and one prosimian galago. Retrograde tracers were injected into neurophysiologically defined representations of individual digits of area 3b. Cortical tissues were cut parallel to the surface in some cases and showed that feedback projections to individual digits overlapped extensively in the hand representations of areas 3b, 1, and parietal ventral (PV) and second somatosensory (S2) areas. Other regions with overlapping populations of labeled cells included area 3a and primary motor cortex (M1). The results were confirmed in other cases in which the cortical tissues were cut in the coronal plane. The same cases also showed that cells were primarily labeled in the infragranular and supragranular layers. Thus, feedback projections to individual digit representations in area 3b mainly originate from multiple digits and other portions of hand representations of areas 3b, 1, PV, and S2. This organization is in stark contrast to the segregated thalamocortical inputs, which originate in single digit representations and terminate in the matching digit representation in the cortex. The organization of feedback connections could provide a substrate for the integration of information across the representations of adjacent digits in area 3b. J. Comp. Neurol. 521:3768–3790, 2013. © 2013 Wiley Periodicals, Inc.     

Thalamic projections to motor, prefrontal, and somatosensory cortex in the sheep studied by means of the horseradish peroxidase retrograde transport method

In this study the motor, prefrontal, and somatosensory areas of the sheep cerebral cortex were defined on the basis of their thalamic afferents traced with the horseradish peroxidase method. The motor area (areas 4 and 6) occupies the cruciate gyrus. It receives a substantial projection from the thalamic nuclei ventralis anterior, ventralis lateralis, medialis dorsalis, and centralis lateralis and a smaller one from the nuclei ventralis medialis, centralis medialis, paracentralis, lateralis dorsalis, lateralis posterior, centromedianus, parafascicularis, suprageniculatus, ventralis posterolateralis, and the midline nuclei. Area 4 receives afferents mainly from the nuclei ventralis anterior, ventralis lateralis, medialis dorsalis, and lateralis posterior, whereas area 6 receives afferents mainly from the nuclei ventralis anterior, medialis dorsalis, and lateralis posterior and fewer afferents from the nucleus ventralis medialis. The prefrontal area occupies the gyrus proreus and receives numerous afferents from the nucleus medialis dorsalis and fewer from the nuclei lateralis posterior and ventralis medialis. The area extending between the lateral fissure, the coronal sulcus, the presylvian sulcus, and the rostral branch of the lateral fissure is connected mainly with sensory thalamic nuclei. Thalamic afferents were found to emanate from the nuclei ventralis posteromedialis (its parvicellular part included), ventralis posterolateralis, ventralis medialis, paracentralis, lateralis posterior, medialis dorsalis, centromedianus, suprageniculatus, paraventricularis, the substantia nigra, and the ventral part of the lateral geniculate nucleus. The first somatosensory area (Johnson et al., '74, J. Comp. Neurol. 158:81-108) was found to extend between the coronal, the diagonal, and the anterior suprasylvian sulci and to receive afferents almost exclusively from the nucleus ventralis posteromedialis.     

Cortical connections of subdivisions of inferior temporal cortex in squirrel monkeys.

Patterns of cortical connections and architectonics were used to determine subdivisions of inferior temporal (IT) cortex of squirrel monkeys. Single or multiple injections of the tracers wheat germ agglutinin-horseradish peroxidase, Fast Blue, Diamidino Yellow, Fluoro-Gold, and 3H-amino acids were placed into IT cortex. Most injections were placed in caudal IT cortex in the region previously shown to receive input from the caudal subdivision of the Dorsolateral Area, DLC; additional injections were placed in more rostral IT cortex. The results indicate the presence of two major regions: a caudal region, ITC, and a rostral region, ITR. An intermediate region of cortex along the ITC-ITR border that displays some connections of ITC and some connections of ITR may be another area. ITC contains a more myelinated dorsal area, ITCd, and a larger ventral area, ITCv. Both ITCd and ITCv receive a major projection from DLC; additional input from DLR, MT, and VII; and send strong projections to ITR, the lateral bank of the superior temporal sulcus, and dorsolateral prefrontal cortex. Only ITCd has strong connections with DLR and cortex in the depths of the superior temporal sulcus, and only ITCv has connections with lateral orbital cortex. The overall pattern of connections between ITC and DLC suggests that ITC has a crude topographic organization, with dorsal cortex representing the lower field and ventral cortex representing the upper field. ITR differs from ITC by receiving little if any input from DLC; projecting to inferior temporal polar cortex, the rostral Sylvian fissure, and medial orbital cortex; and having a less distinct layer IV. Comparison of subdivisions of inferior temporal cortex defined in the present study in squirrel monkeys and those reported in other primates suggests that ITC of squirrel monkeys may correspond to area TEO of macaque monkeys.     

Development of connections between the mediodorsal nucleus of the thalamus and the prefrontal cortex in the rat

The postnatal ingrowth of thalamocortical fibers from the mediodorsal nucleus to the prefrontal cortex was investigated in relation to the development of cortical lamination. Like the dopaminergic fibers in the prefrontal cortex and the thalamic fibers in the visual cortex, the mediodorsal fibers have entered the prefrontal cortex at birth. Most of the fibers are found in the developing layer VI, but, in contrast to the above-mentioned systems, a considerable number of mediodorsal fibers have already penetrated into the upper, most immature part of the cortical plate on postnatal day 1. From day 1 to day 7 an increasing number of mediodorsal fibers reach the upper cortical plate, which by then is developing layer III, the terminal layer of these fibers. The reciprocal connection from the layer VI cells of the prefrontal cortex to the mediodorsal nucleus develops between day 4 and day 9. Finally, the projection from the contralateral prefrontal cortex to the mediodorsal nucleus is established around day 10. The early presence of the mediodorsal fibers in the upper, differentiating cortical plate might indicate an important role for the mediodorsal fibers in the laminar development of the prefrontal cortex.     

Lateral magnocellular thalamic nucleus in rabbits: architecture and projections to cingulate cortex.

The lateral magnocellular nucleus (LM) contains the largest neurons in the rabbit thalamus, yet its cortical connections have not been described. This study evaluates the architecture, cingulate cortical connections, and spontaneous rate of neuronal discharges in LM. At its maximal mediolateral extent in coronal sections, LM underlies the laterodorsal and lateroposterior nuclei. It has a short medial and long lateral limb, both of which have high levels of cytochrome oxidase activity. On the basis of horseradish peroxidase and fluorescent dye injections, LM projects primarily to area 29 and posterior area 24. Projections to area 29d are topographically organized so that the medial limb of LM projects to rostral area 29d, mid levels of LM where the limbs join project to midlevels of area 29d and lateral parts of the lateral limb project to posterior area 29d. It is mainly the midportion of the lateral and medial limbs that projects to areas 29b and 29c. The anterior parts of these areas receive input from dorsal parts of LM, whereas posterior levels of these areas receive input from ventral LM. The midregion of LM also projects to caudal area 24. Injections of 3H-amino acids into area 29d anterogradely label neuronal processes in LM. Finally, single unit electrophysiological recordings from LM in halothane-anesthetized rabbits showed a unique pattern of spontaneous discharges. Over 70% of the LM neurons cycled through a number of different phases with a mean +/- S.E.M. peak discharge rate of 31 +/- 4.7 Hz. This high rate contrasts with the 17.6 +/- 3.2 Hz rate for neurons that maintained a constant rate of discharge and the 7.5 +/- 1.3 Hz rate of discharges for neurons in nuclei dorsal and ventral to LM. LM neurons are large, have high levels of cytochrome oxidase and spontaneous activity, and project extensively to the posterior cingulate cortex. These features suggest that LM neurons are highly active metabolically and may be fast conducting efferents to cingulate cortex.     

Neurochemical organization of inferior pulvinar complex in squirrel monkeys and macaques revealed by acetylcholinesterase histochemistry, calbindin and Cat-301 immunostaining, and Wisteria floribunda agglutinin binding.

To investigate whether the inferior pulvinar complex has a common organization in different primates, the chemoarchitecture of the visual thalamus was re-examined in squirrel monkeys (Saimiri sciureus) and macaques (Macaca mulatta). The inferior pulvinar (PI) complex consisted of multiple subdivisions and encompassed the classic PI, and adjacent ventral parts of the lateral and medial pulvinar (PL and PM, respectively). In keeping with nomenclature suggested previously for macaques, the PI subdivisions were termed the posterior, medial, central, lateral, and lateral-shell (PI(P), PI(M), PI(C), PI(L), and PI(L-S)). In both species, PI(P) was intense for calbindin, light for acetylcholinesterase (AChE), and very light for Wisteria floribunda agglutinin (WFA) histochemistry. The PI(M) was calbindin poor, AChE rich, and moderate for WFA. The PI(C) was calbindin intense, lighter for AChE, and exhibited little WFA binding. PI(L) and PI(L-S) contained populations of large calbindin or WFA cells that were more numerous in PI(L-S). Although staining with the monoclonal antibody Cat-301 differed between macaques and squirrel monkeys, the same subdivisions were displayed. Moderately dense, patchy Cat-301 stain was found in PI(M) of macaques, whereas in squirrel monkeys PI(M) was light. Connections of the rostral dorsolateral (DLr) and middle temporal (MT) areas of visual cortex in squirrel monkeys were compared with PI subdivisions revealed by the newer histochemical methods in the same cases. The major connections of DLr were with PI(C) and of MT were with PI(M).     

Corticothalamic connections from the second somatosensory area and neighboring regions in the lateral sulcus of macaque monkeys

Corticothalamic connections were shown between the second somatosensory area in primates and the ventroposterior nuclei of the thalamus. These projections were topographically arranged with those from the hindlimb portions of SII traced to the most lateral and posterior parts of the ventroposterior lateral nucleus (VPLc) and those from the forelimb located medially within VPLc. The densest labeling was found ventrally in VPLc and dorsally within ventroposterior inferior n. (VPI) only after injections of the forelimb. A more scattered, dorsal distribution of labeling was seen in the rest of VPLc from injections involving more proximal parts of the body representation in SII.     

Connections between the thalamus and the somatosensory areas of the anterior ectosylvian gyrus in the cat

The thalamocortical and corticothalamic connections of the second somatic sensory area (SII) and adjacent cortical areas in the cat were studied with anterograde and retrograde tracers. Injections consisted of horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA) or a mixture of equal parts of tritiated leucine and proline. The cortical regions to be injected were electrophysiologically studied with microelectrodes to determine the localization of the selected components of the body representation in SII. The distribution of recording points was correlated in each case with the extent of the injection mass in the cortex. Distributions of retrograde and anterograde labeling in the thalamus were reconstructed from serial coronal sections. The results from cases with injections of tracers exclusively confined to separate parts of the body map in SII indicated a fairly precise topographical organization of projections from the ventrobasal complex (VB) to SII. The labeled cells and fibers were located within a series of lamella-like rods that curved throughout the dorsoventral and rostrocaudal axis of VB. The position and extent of these lamellae shifted from medial and ventral, in the medial subdivision of ventral posterior lateral nucleus (VPLm) for radial forelimb digit zones of SII, to dorsal, Posterior, and lateral, in the lateral subdivision of ventral posterior lateral nucleus (VPLl) for proximal leg and trunk regions in SII. For every injected area in SII the densest clustering of labeled cells and fibers was usually more posteriorly represented in VB. The distribution in these dense zones of labeling often extended through the central core of VB. SII projecting neurons were also consistently noted in the extreme rostral portion of the medial subdivision of the posterior nuclei (Pom) that lies dorsal to VB. Corticothalamic and thalamocortical connections for SII Were entirely reciprocal. Injections of tracers into cortical areas surrounding SII labeled other parts of the posterior complex but failed to label any part of VB except when the injection mass also diffused into SII. Injections into the somatic sensory cortex located lateral to SII, within the lips and depth of the upper bank of the anterior ectosylvian sulcus (AES), heavily labeled the central and posterior portions of Pom. Substantial labeling was noted in the lateral (Pol) and intermediate (Poi) divisions of Po only when the injections involved some part of the auditory area that occupies the most posterior part of the AEG and both banks of the immediately adjoining AES. The magnocellular nucleus of the medial geniculate (MGmc) was labeled only when some part of the auditory cortex was injected. The suprageniculate nucleus (SG) was labeled from the insula and lower bank of the AES. These results indicated that medial (rostral and caudal Pom) and lateral components (Poi, Pol, MGmc) of the Posterior complex have separate cortical projection zones to somatic sensory and auditory cortical regions, respectively. SIV and the lateral extent of area 5a located in the medial bank of the anterior suprasylvian sulcus sent projections to the deep layers of the supe- rior colliculus and the ventrolateral periaqueductal gray. No cortico-tectal projections were seen from SII.     

Geometry and orientation of thalamocortical arborizations in the cat somatosensory cortex as revealed by computer reconstruction

The geometry of the intracortical arborization of single neurons from the ventroposterolateral thalamic nucleus in cat was studied with computer reconstruction after intraaxonal injections of horseradish peroxidase in fibers whose receptive field had been identified. The terminal arbors of slowly (SA) and rapidly (RA) adapting thalamocortical neurons were often (60%) composed of two separated bushes of 300-600 microns in diameter separated by a region of about the same size containing much less terminal ramifications. The bushes were aligned mainly along the mediolateral axis of the brain. It is proposed that this structural feature underlies the RA-SA banding already described in the somatosensory areas by physiological experiments.     

Crosstalk between the two sides of the thalamus through the reticular nucleus: A retrograde and anterograde tracing study in the rat

In order to investigate the possible routes linking the thalamus in the two sides of the brain, the connections of the reticular nucleus (RT), the major component of the ventral thalamus, with contralateral dorsal thalamic nuclei were systematically investigated in the adult rat. This study was performed with several tract-tracing techniques: single and double retrograde labeling with fluorescent tracers, and anterograde tracing with biocytin. Retrograde tracing was also combined with immunocytochemistry to provide additional criteria for the identification of labeled RT neurons. The data obtained with the retrograde transport of one fluorescent tracer showed that RT neurons project to contralateral dorsal thalamic domains. In particular, retrograde labeling findings indicated that the anterior intralaminar nuclei, as well as the ventromedial (VM) nucleus, are preferential targets of the contralateral RT projections. Commissural neurons were concentrated in two portions of RT: its rostral part, including the rostral pole, which projects to the contralateral central lateral (CL) and paracentral (Pc) nuclei, and the ventromedial sector of the middle third of RT, which projects to the contralateral VM and posterior part of CL and Pc. The double retrograde labeling study of the bilateral RT–intralaminar connection indicated that at least part of the commissural RT cells bifurcate bilaterally to symmetrical portions of the anterior intralaminar nuclei. The targets of the RT commissural system inferred from the retrograde labeling data were largely confirmed by anterograde tracing. Moreover, it was shown that RT fibers cross the midline in the intrathalamic commissure. The present data demonstrate that bilateral RT connections with the dorsal thalamus provide a channel for interthalamic crosstalk. Through these bilateral connections with thalamic VM and intralaminar neurons, RT could influence the activity of wide territories of the cerebral cortex and basal ganglia of both hemispheres. © 1993 Wiley-Liss, Inc.     

Representation of face and intra-oral structures in area 3b of macaque monkey somatosensory cortex

Details of the representation of body regions innervated by the trigeminal nerve were elucidated in monkey cerebral cortex. Microelectrode recording was used to generate somatosensory maps in the posterior bank of the central sulcus and on the exposed cortical surface lateral to the lateral tip of the central sulcus in Macaca nemestrina. The area innervated by the contralateral trigeminal nerve is represented in an 8-mm mediolateral extent of area 3b lateral to the representation of the hand. Lateral to this, still within area 3b, there is an expanded representation of ipsilateral intra-oral structures measuring 6 mm in mediolateral extent. Both representations fill area 3b anteroposteriorly. The ipsilateral representation forms approximately 40% of the trigeminal representation, consistent with the amount of the ventroposterior medial (VPM) thalamic nucleus devoted to representation of ipsilateral intra-oral structures. Comparison of the present results with maps of the face representation in other species of monkey shows a consistent somatotopy of the face between species; size variations are mainly related to the enlarged ipsi- and contralateral representations of the cheek pouches in macaques. The general somatotopy of the trigeminal representation in monkeys is consistent with that in other mammalian species. © 1996 Wiley-Liss, Inc.     

The inferior pulvinar complex in owl monkeys: architectonic subdivisions and patterns of input from the superior colliculus and subdivisions of visual cortex.

Patterns of connections with other visual structures and architectonic characteristics were used to subdivide the inferior pulvinar complex of owl monkeys into three distinct nuclei termed the central inferior pulvinar, IPc, the medial inferior pulvinar, IPm, and the posterior inferior pulvinar, IPp. IPc occupies about 70%; IPm about 20%, and IPp about 10% of the inferior pulvinar complex. Encapsulating fiber bands distinguish the boundaries of the three nuclei. IPm is also identified by a much greater packing density of neurons than IPc and IPp. Both IPp and IPc receive input from the superior colliculus, but the terminations in IPp are denser. Visual cortical Areas 17, 18, MT, DM, M and PP (Allman and Kaas, '76) project to IPc and IPm in patterns that indicate that central vision is represented dorsorostrally and peripheral vision ventrocaudally in both nuclei. Terminations in IPm from Area MT are particularly dense. None of these visual areas projects to IPp. Rather, input to IPp appears to originate in cortex rostral to Area MT in the temporal lobe.     

Parallel thalamic activation of the first and second somatosensory areas in prosimian primates and tree shrews.

In Tupaia belangeri and Galago senegalensis, microelectrode recordings immediately after ablation of the representation of the forelimb in the midportion of the first somatosensory area, S-I, revealed that all parts of the second somatosensory area, S-II, remained highly responsive to cutaneous stimuli. In this way, prosimian primates, close relatives of simian primates, and tree shrews differ markedly from monkeys in which S-II is deactivated by comparable ablations, and resemble such mammals as cats and rabbits in which S-II also remains highly responsive following ablations in S-I. Thus, it appears that the generalized mammalian condition is that S-I and S-II are independently activated via parallel thalamocortical pathways. A dependence of S-II on serial connections from the thalamus to the S-I region and then to S-II apparently evolved with the advent of anthropoid primates, and may be present only in monkeys and perhaps other higher primates.     

Representation of the face and intraoral structures in area 3b of the squirrel monkey (Saimiri sciureus) somatosensory cortex,with special reference to the ipsilateral representation

Studies of the representation of the trigeminal nerve in the thalamus and cerebral cortex of mammals have revealed representations of both contra- and ipsilateral intraoral structures. However, the relative extent of both representations is subject to considerable species variation. The present study employed microelectrode mapping and anatomical tracing to investigate the location and extent of the ipsilateral representation in area 3b of the somatosensory cortex of squirrel monkeys. A small region, approximately 2 mm², was found to be responsive to stimulation of ipsilateral intraoral structures. This region was located on the anteromedial border of area 3b, surrounded by the representation of the contralateral roof of the mouth. This region corresponded to areas of intense anterograde labeling following injections placed in the ventromedial portion of the ventral posterior medial nucleus of the thalamus at the only sites where neural responses could be elicited by stimulation of ipsilateral intraoral structures. The amount of thalamus and cortex given over to the ipsilateral representation in the squirrel monkey is small compared with that of the macaque monkey. This difference may be related to the lack of cheek pouches in the squirrel monkey, and therefore a different strategy for eating. The representation of the contralateral lower lip in area 3b was split by the representation of the contralateral upper lip. This split representation is in agreement with previous studies of the trigeminal representation in area 3b of the macaque monkey and may be a general feature of the representation of the trigeminal nerve in area 3b of primate cerebral cortex. © 1995 Wiley-Liss Inc.     

Mediodorsal nucleus: areal, laminar, and tangential distribution of afferents and efferents in the frontal lobe of rhesus monkeys

The terminal distribution of thalamic afferents in primate prefrontal cortex has never been examined in any detail. In the present study, WGA-HRP was injected into major subdivisions of the mediodorsal nucleus (MD) in the rhesus monkey in order to determine 1) The areal distribution of MD projections, 2) the layer(s) in which MD afferents terminate, 3) the tangential pattern of the MD axonal terminals, 4) the cells of origin of the reciprocal corticothalamic pathway, and 5) the degree of reciprocity between the corticothalamic and thalamocortical pathways in the different regions of the prefrontal cortex. As expected on the basis of retrograde degeneration and transport studies, injections centered in the magnocellular (MDmc) subnucleus of MD labeled cells and terminals in the ventral and medial prefrontal cortex. Injections involving ventral MDmc labeled the more lateral of these areas (Walker's areas 11 and 12); injections of the dorsal MDmc labeled the ventromedial regions (areas 13 and 14). In contrast, injections involving mainly the lateral, parvicellular (MDpc) moiety labeled cells and terminals in dorsolateral and dorsomedial areas (Walker's 46, 9, and 8B). Area 8A was labeled most prominently when injections included the multiform portion of MD (MDmf) and area 10 had connections with anterior portions of MD. A dorsal-ventral topography for MDpc exists with dorsal MDpc labeling dorsal and dorsomedial prefrontal areas and ventral MDpc labeling dorsolateral prefrontal cortex. Our findings with respect to MD are consistent with a nucleus-to-field organization of its thalamocortical projection system. Outside of the traditional boundaries of prefrontal cortex, lateral MD projections extended to the supplementary motor area (SMA) and the dorsal part of the anterior cingulate (AC) whereas the medial MD projection targeted the ventromedial cingulate cortex and spared SMA. In addition, a few labeled cells and sparse terminals were found in the inferior parietal lobule, the superior temporal sulcus, and the anterior part of the insula after injections that involved the medial part of MD. Labeled terminals were invariably confined to layer IV and adjacent deep layer III. No terminal label was ever observed in layers I, II, superficial III, V, or VI in any part of the cerebral cortex following injections confined to any part of MD.(ABSTRACT TRUNCATED AT 400 WORDS)     

Connections of areas 3b and 1 of the parietal somatosensory strip with the ventroposterior nucleus in the owl monkey (Aotus trivirgatus).

Anatomical tracers were injected into electrophysiologically defined sites in somatosensory cortical Area 3b (SI proper) and Area I (posterior cutaneous field) of owl monkeys after these cortical subdivisions had been extensively explored in microelectrode mapping experiments. These mapping experiments revealed that both Areas 3b and 1 contain complete and separate representations of the body surface (Merzenich et al., '78). Restricted injections of the retrograde tracer, horseradish peroxidase (HRP), into either Area 3b or Area 1 labeled neurons within a band of cells in the ventroposterior nucleus (VP). The location of the labeled band in VP varied with the location of the injection site in both representations, and the labeled region of VP was overlapping for injections in corresponding body parts in the two representations. Neurons projecting to the hand and foot cortical representations were in architectonically identified subnuclei. Because injections into either Area 3b or Area 1 labeled over half of the neurons in the appropriate regions of VP, it appears that some neurons in VP project to both cortical representations. Finally, injections of HRP combined with the anterograde tracer, 3H-proline, indicate that VP neurons are reciprocally interconnected with both Areas 3b and 1.     

Representations of the face, teeth and oral cavity in areas 3b and 1 of somatosensory cortex in squirrel monkeys

The somatotopic organization of low threshold inputs from the face and head was determined in the lateral portion of areas 3b and 1 in squirrel monkeys. A complete, topographically organized representation was found in area 3b, and a separate, roughly parallel representation was found in adjacent area 1. In addition, there was evidence for remarkable individual variability in the representation of the lips in area 3b.