Modular segregation of functional cell classes within the postcentral somatosensory cortex of monkeys.

The distribution of two functionally distinct cell types, presumably related to slowly and rapidly adapting mechanoreceptors in the skin, was explored within the representation of the glabrous hand in area 3b of the somatosensory cortex of monkeys. The two cell classes lie in relatively segregated alternating anteroposterior bands within the middle layers of the cortex.

Recovery of normal topography in the somatosensory cortex of monkeys after nerve crush and regeneration.

After median nerve fibers to glabrous skin on the hands of monkeys were crushed and allowed to regenerate, normal topographical organization was recovered in the representation of the hand in primary somatosensory cortex. Similar recovery of normal cortical organization may underlie the sensory restoration that usually follows nerve crush injury in humans.

Evidence for brainstem and supra-brainstem contributions to rapid cortical plasticity in adult monkeys.

Cortical maps can undergo amazingly rapid changes after injury of the body. These changes involve functional alterations in normal substrates, but the cortical and/or subcortical location(s) of these alterations, and the relationships of alterations in different substrates, remain controversial. The present study used neurophysiological approaches in adult monkeys to evaluate how brainstem organization of tactile inputs in the cuneate nucleus (CN) changes after acute injury of hand nerves. These data were then compared with analogous data from our earlier cortical area 3b studies, which used the same approaches and acute injury, to assess relationships of cuneate and cortical changes. The results indicate that cuneate tactile responsiveness, receptive field locations, somatotopic organization, and spatial properties of representations (i.e., location, continuity, size) change during the first minutes to hours after injury. The comparisons of cuneate and area 3b organization further show that some cuneate changes are preserved in area 3b, whereas other cuneate changes are transformed before being expressed in area 3b. The findings provide evidence that rapid reorganization in area 3b, in part, reflects mechanisms that operate from a distance in the cuneate nucleus and, in part, reflects supracuneate mechanisms that modify brainstem changes.

Functional organization of tactile inputs from the hand in the cuneate nucleus and its relationship to organization in the somatosensory cortex.

Central processing of tactile inputs from the hand begins in the main cuneate nucleus and continues in the thalamus and area 3b cortex. Little is known about cuneate functional organization in primates or about how cuneate and area 3b organization are related. In this study, neurophysiologic approaches were used to evaluate how tactile inputs from the hand and adjacent body are organized in the cuneate nucleus of squirrel monkeys. Cuneate data on the organization of hand inputs were then compared with analogous area 3b data from our earlier cortical studies that used the same approaches. Evaluations of several cuneate properties, including (1) responsiveness to tactile stimulation, (2) incidences and sizes of receptive fields, (3) somatotopic progressions, (4) properties of representations, and (5) relationships between functional inputs and cytochrome oxidase staining, suggest that tactile afferents from the hand form consistently organized cuneate representations that, in turn, relate to the parcellated organization of cuneate structural substrates. Comparisons of cuneate and area 3b organization indicate that tactile processing from the brainstem to cortex involves a preservation of tactile responsiveness and somatotopic organization but, in addition, involves transformations that produce receptive field sharpening, suppression of hairy hand inputs, amplification and refinement of glabrous inputs, and relocations of representations. Ascending lemniscal substrates are characterized by cascading excitatory convergence/divergence that increments at successively higher levels between sensory afferents and area 3b. It is suggested that the observed preservations and transformations reflect this organization but, in addition, reflect mechanisms that cause counterbalancing sharpening and suppressions of hand inputs.

Nerve innervation of the hand and associated nerve dominance aggregates in the somatosensory cortex of a primate (squirrel monkey).

The cutaneous innervation territories of the median, ulnar, and radial nerves to the hand were determined from neurophysiological recordings of peripheral mechanoreceptor axons in adult squirrel monkeys. These territories were then related to cutaneous receptive fields of cortical area 3b neurons to determine how low-threshold inputs from each hand nerve map onto the primary somatosensory cortex. The results indicate that mechanoreceptor axons in each nerve innervate a continuous skin territory covering about 40% of the hand surface. The total territory of each nerve contains subregions of skin that are either autonomously innervated by that nerve or that receive overlapping innervation from more than one nerve. The autonomous, overlap, and total territories of each nerve are relatively constant from hand to hand. In the area 3b cortex, low-threshold afferents from each nerve provide inputs to aggregates of cortical neurons. The cortical aggregates relating to the median and ulnar nerves are arranged as continuous, rostrocaudally oriented bands, whereas aggregates relating to the radial nerve are discontinuous and more patch-like. Similar patterns of bands and patches, and similar compression ratios of skin/cortical area, are seen across different monkeys. These findings demonstrate that the primary somatosensory cortex of normal adult primates contains bands or patches of neurons that are dominantly activated by low-threshold inputs from specific hand nerves. This approach of delineating nerve territories and their related cortical dominance aggregates provides a useful means of analyzing cortical images of nerves and of quantitating peripheral and central patterns of deprivation after nerve injury.

Somatotopic organization of inputs from the hand to the spinal gray and cuneate nucleus of monkeys with observations on the cuneate nucleus of humans.

Central termination patterns of primary afferents from the hand and forelimb were studied following subdermal injections of HRP conjugates in macaque monkeys. In the middle layers of the dorsal horn of the spinal cord, afferents from digits 1-5 terminated in a rostrocaudal sequence in separate, elongated columns at cervical levels 5-7. Afferents from the glabrous digits extended to the medial margin of the dorsal gray, while afferents from the dorsal skin of the digits terminated more laterally. Afferents from the dorsal hand and palm terminated lateral to those from the digits, while inputs from the forearm occupied tissue rostral and caudal to the representation of the hand. In the cuneate nucleus, terminations from each digit formed an elongated column that was densely labelled in the central pars rotunda and sparsely labelled in both the rostral and caudal reticular poles. Within the pars rotunda, digits 1-5 were represented in order from lateral to medial. Inputs from the digit tips terminated ventral to inputs from the proximal digits. Afferents from the dorsal skin of the digits terminated in an even more dorsal position, while the most dorsal portion of the pars rotunda related to the glabrous and dorsal hand. Within the pars rotunda, terminations from specific parts of the hand overlapped parcellated clusters of neurons. These clusters were densely reactive for cytochrome oxidase (CO) and were surrounded by myelinated fibers. Much sparser label in the reticular poles was found consistently only after injections in the glabrous digits. Inputs to the poles appeared diffuse and overlapping while preserving some somatotopic order. When treated for CO or stained for Nissl substance or myelin, the pars rotunda of humans showed parcellation patterns that closely resembled the patterns seen in monkeys. From the relationship of inputs to the CO dense cell clusters in monkeys, it was possible to postulate in detail the somatotopic organization of inputs to pars rotunda of humans. The present results provide a comprehensive description of the somatotopic patterns of termination of afferents from the skin of the hand and forearm in the spinal cord and cuneate nucleus of macaque monkeys. A direct relationship of afferent somatotopy and identifiable cell clusters in the pars rotunda of the cuneate nucleus is further demonstrated. Finally, the patterns of cell clusters in the pars rotunda of macaque monkeys and humans suggest that the somatotopic organization of the cuneate nucleus may be very similar in human and nonhuman primates.

Cortical connections of the middle temporal visual area (MT) and the superior temporal cortex in owl monkeys.

The connections of the middle temporal visual area (MT) and an adjoining superior temporal visual region (ST) were investigated with injections of 3H-proline and horseradish peroxidase (HRP) in adult owl monkeys. Injections in MT revealed an extensive pattern of intrinsic connections that appeared to be organized in a series of bands across MT. MT was found to project ipsilaterally to an array of visual areas including the first (V I) and second (V II) visual areas, the dorsolateral visual area (DL), and the dorso-medial visual area (DM). When injection sites and projection zones were related to previously described retinotopic maps, it was apparent that the projections of MT to these fields were largely homotopic. Other projections were to posterior parietal cortex, the dorsointermediate visual area (DI), the ventral visual area (V), and possibly the medial visual area (M). In addition, dense projections to cortex on the rostral border of MT were used to define a new subdivision of visual cortex, the superior temporal visual region (ST), as the major projection zone of MT. Callosal connections of MT were mainly to MT, with some terminations in DL and ST. Injections of 3H-proline into ST revealed a diffuse projection to largely layer I of MT, and dense projections to posterior parietal cortex, cortex in more rostral parts of the superior temporal sulcus, ventromedial inferior temporal cortex, and the region of the frontal eye fields. Callosal projections were largely to ST cortex of the other cerebral hemisphere. The results place MT and V II in distinctly different processing chains. While both MT and V II receive the major cortical outputs of V I, V II relays to DL and DL relays to subdivisions of inferior temporal cortex. In contrast, the most significant cortical target of MT appears to be to ST, which relays to posterior parietal cortex and other targets.

Cortical and subcortical projections of the middle temporal area (MT) and adjacent cortex in galagos.

Projections of the middle temporal visual area, MT, and of visual cortex adjoining MT were investigated with autoradiographic methods in the prosimian primate, Galago senegalensis. Ipsilateral cortical targets of MT included area 17, area 18, cortex caudal to MT, cortex ventral to MT, and parietal-occipital cortex dorsal to MT. This pattern of projections suggests that extrastriate cortex contains a number of visual subdivisions in addition to MT. Contralateral projections were to MT and parietal-occipital cortex. Projections from MT to areas 17 and 18 connected regions representing similar parts of the visual hemifield while the location of callosal projections in MT matched the location of the injection site in the other hemisphere. Label in area 17 was concentrated in layers I, III, and VI whereas other cortical areas were most densely labeled in the granular and supragranular layers. Subcortical projections of MT included the reticular nucleus of the thalamus, the lateral posterior nucleus, the superior pulvinar, the inferior pulvinar, the superior colliculus, and the pontine nuclei. The projection pattern to the superior and inferior pulvinar nuclei suggests that MT projects in a topographic manner to two subdivisions within each of these structures. Injections in cortex just outside of MT labeled area 18, inferotemporal cortex, parietal-occipital cortex, and, to a lesser extent, MT. The projections to inferotemporal cortex clearly distinguish the bordering cortex from MT. Contralateral cortical terminations were in locations corresponding to the injection site. Subcortical targets were generally similar to those seen after MT injections, although additional projections were observed depending on the location of the injection. Comparison of these results from the prosimian galago with studies in New and Old World monkeys indicates there are substantial similarities in projections. Thus, some of the cortical and thalamic subdivisions described for monkeys appear to exist in prosimians.

Central projections from the skin of the hand in squirrel monkeys.

Central termination patterns of afferents from the hands of squirrel monkeys were studied after subdermal injections of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) or cholera toxin subunit B conjugated to HRP (BHRP). WGA-HRP more effectively labeled axons terminating in the superficial dorsal horn of the spinal cord, while BHRP more effectively labeled axons terminating in the deeper layers. Injections of both tracers, when restricted to parts of glabrous digits, palm, or dorsal hand, revealed somatotopic patterns in the spinal cord and pars rotunda of the cuneate nucleus that were, in some respects, similar and, in other respects, quite different from those previously reported for macaque monkey (Florence et al., J. Comp. Neurol. 286:48-70, '89). As in macaques, injections in digits 1-5 produced a rostrocaudal sequence of foci of terminations in the cervical spinal cord. However, inputs from the palm were located medial to those from the digits, whereas the palm is represented lateral to the digits in macaque monkeys. Since inputs from the palm is also medial in the dorsal horn in cats (Nyberg and Blomqvist, J. Comp. Neurol. 242:28-39, '85), the condition in squirrel monkeys may be similar to the generalized state. In the cuneate nucleus, single injections in the hand produced dense label in the pars rotunda, and sparse label in the rostral and caudal poles. As in macaque monkeys, inputs from specific parts of the hand related to rostrocaudal clusters of cells that are cytochrome oxidase dense. The representation of the digits differed from macaques in that the digits were represented dorsal to the palm, rather that ventral to the palm as in macaques. Again, comparisons with cats suggest that squirrel monkeys have the more generalized pattern. Finally, inputs from the hair, dorsal surfaces of the digits terminated on the same clusters as the inputs from the glabrous, ventral surfaces, apparently overlapping somewhat. The proximity of these terminations from dorsal and ventral surfaces of the digits may be related to observations that cortical representations of the glabrous surfaces of digits become responsive to dorsal surfaces of the same digits when inputs from glabrous skin are chronically deactivated (e.g., Merzenich et al., Neuroscience 3:33-55, '83).

Initial cortical reactions to injury of the median and radial nerves to the hands of adult primates.

The area 3b hand cortex of adult squirrel monkeys was mapped during the first minutes to hours after transecting the radial and median nerves to the hand. The objective was to evaluate initial cortical reactions to this injury and to determine whether patterns and extents of cortical change are similar in different individuals. There are 5 main findings. First, cortical aggregates related to ulnar nerve inputs from the hand rapidly expanded to occupy an additional 21% of the cortical hand map. Second, face and forearm inputs, which normally activate areas adjacent to hand cortex, rapidly expanded into areas of 4% and 1% of the hand cortex respectively. Third, cortical changes involved shifts in receptive field locations that were initiated within minutes after injury. Fourth, the spatial patterns and extents of cortical change were similar in different individuals. Finally, the pattern of cortical change produced after this injury differed from the pattern seen after injury of the median and ulnar nerves. These rapid expansions are a beginning point from which further changes must progress; however, in contrast to changes accompanying chronic hand injuries, these initial cortical reactions do not appear dictated by use of uninjured inputs.

Cortical organization after treatment of a peripheral nerve with ricin: an evaluation of the relationship between sensory neuron death and cortical adjustments after nerve injury.

The present study was designed to assess whether cortical changes after peripheral nerve damage are related to the degree of death of primary sensory neurons in the damaged nerve. The cytotoxin ricin was injected into the sciatic nerves of adult rats to kill primary sensory neurons with axons through the injection site. Following periods of 6-101 days, the S-I hindpaw map was evaluated with neurophysiological techniques and compared with the hindpaw maps of previously studied normal adult rats and adult rats that had undergone adult or neonatal sciatic section at a comparable level of the nerve. These comparisons allowed evaluation of cortical functional organization following different degrees of sensory neuron loss after sciatic nerve injury. There were three main results. 1) The comparison of ricin-treated and normal adult rats indicated that ricin treatment interrupted inputs from the sciatic skin territory on the hindpaw and caused a limited increase in the size of the cortical area that was activated by stimulation of hindpaw skin innervated by the remaining saphenous nerve. 2) The cortical maps of rats that had undergone adult ricin treatment (relatively large primary neuron loss) or section during adulthood (small to moderate primary neuron loss) were similar. In both groups, only the saphenous hindpaw skin was represented in cortex, and the cortical area that was activated by stimulation of the saphenous hindpaw skin had undergone a comparable limited enlargement. 3) The comparison of ricin-treated adult rats (relatively large primary neuron loss) and adult rats that had undergone neonatal section (relatively large primary neuron loss) indicated that cortical organization differed after these treatments. In particular, after ricin treatment the cortical area that was activated by stimulation of the saphenous hindpaw skin was larger than the comparable area in neonatal denervates, and the topographical progressions between the hindpaw and adjacent body representations were not as variable as after neonatal section. These findings indicate that cortical maps are altered after injection of ricin into a nerve. The similarity in cortical organization after ricin treatment (relatively large sensory neuron loss) and nerve section in adults (relatively small sensory neuron loss) and the differences in cortical organization after ricin treatment and nerve section in neonates (both relatively large sensory neuron loss) indicate cortical changes do not covary as a simple function of the degree of peripheral neuron death.

Somatotopic organization of the lateral sulcus of owl monkeys: area 3b, S-II, and a ventral somatosensory area.

Multiunit microelectrode recordings and injections of horseradish peroxidase (HRP) were used to reveal neuron response properties, somatotopic organization, and interconnections of somatosensory cortex in the lateral sulcus (sylvian fissure) of New World owl monkeys. There were a number of main findings. 1) Representations of the face and head in areas 3b, 1, and S-II are found on the upper bank of the lateral sulcus. Most of the mouth and lip representations of area 3b were found in a rostral extension along the lip of the lateral sulcus. Adjacent cortex deeper in the lateral sulcus represented the nose, eye, ear, and scalp. 2) S-II was located on the upper bank of the lateral sulcus and extended past the fundus onto the deepest part of the lower bank. The face was represented most superficially in the sulcus, with the hand, foot, and trunk located in a rostrocaudal sequence deeper in the sulcus. The orientation of S-II is "erect," with the limbs pointing away from area 3b. 3) Neurons in S-II were activated by light tactile stimulation of the contralateral body surface. Receptive fields were several times larger than for area 3b neurons. 4) A 1-2-mm strip of cortex separating the face and hand representations in S-II was consistently responsive to the stimulation of deep receptors but was unresponsive to light cutaneous stimulation. 5) Injections of horseradish peroxidase in the electrophysiologically identified hand or foot representations of area 3b revealed somatotopically matched interconnections with mapped hand and foot representations in S-II. 6) A systematic representation of the body, termed the "ventral somatic" area, VS, was found extending laterally from S-II on the lower bank of the lateral sulcus. Within VS, the hand and foot were represented deep in the sulcus along the hand and foot regions of S-II, and the face was lateral near the ventral lip of the sulcus. 7) Neurons at most recording sites in the VS region were activated by contralateral cutaneous stimuli. However, a few sites had neurons with bilateral receptive fields. Receptive field sizes were comparable to those in S-II. In addition, neurons in islands of cortex in the VS region had properties that suggested that they were activated by pacinian receptors, while other regions were difficult to activate by light tactile stimuli but responded to stimuli that would activate deep receptors. 8) A few recording sites caudal to S-II on the upper bank of the lateral sulcus were responsive to somatic stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Lesion-induced changes in the central terminal distribution of galanin-immunoreactive axons in the dorsal column nuclei.

Rats that sustained forelimb removal on either embryonic day (E) 16, on the day of birth (P-0), or transection of the brachial plexus in adulthood had brainstem sections stained for galanin, calcitonin gene-related peptide (CGRP), or substance P (SP) at various intervals after these lesions were made. In normal adult rats, only a few galanin-immunoreactive fibers are present in the cuneate nucleus and most are located in its caudal portion. CGRP-positive axons are also sparse in the cuneate and are distributed mainly in the periphery of the nucleus. SP-positive axons are seen throughout the cuneate nucleus. In rats that sustained forelimb removals at birth or transection of the brachial plexus in adulthood, dense galanin immunoreactivity was present throughout the cuneate nucleus at all rostrocaudal levels on the side of the brainstem ipsilateral to the lesion. The changes after lesions that were made in the adult animals were apparent within 1 week, the earliest time analyzed. Increases in galanin immunoreactivity in the cuneate of animals that sustained forelimb removals on P-0 were first visible on P-2. Neither forelimb removal at birth nor brachial plexus lesions in adulthood had any qualitative effect upon the distribution or density of CGRP- or SP-immunoreactivity in the cuneate nucleus. Removal of a forelimb on E-16 did not increase the density of galanin-immunoreactive fibers in the cuneate nucleus. Such lesions also failed to produce any appreciable change in the density of either CGRP- or SP-positive fibers in the cuneate nucleus. The present data raise the possibility that large caliber, non-peptidergic primary afferent axons which innervate the cuneate nucleus may express galanin after damage at birth or in adulthood.

Progression of change following median nerve section in the cortical representation of the hand in areas 3b and 1 in adult owl and squirrel monkeys.

In an earlier study (Neuroscience 8, 33-55, 1983), we found that the cortex representing the skin of the median nerve within parietal somatosensory fields 3b and 1 was completely occupied by 'new' inputs from the ulnar and radial nerves, 2-9 months after the median nerve was cut and tied in adult squirrel and owl monkeys. In this report, we describe the results of studies directed toward determining the time course and likely mechanisms underlying this remarkable plasticity. Highly detailed maps of the hand surface representation were derived in monkeys before, immediately after, and at subsequent short and intermediate time stages after median nerve section. In one monkey, maps were derived before nerve section, immediately after nerve section, and 11, 22 and 144 days later. Thus, direct comparisons in cortical map structure could be made over time in this individual monkey. In other experiments, single maps were derived at given post-section intervals. These studies revealed that: (1) large cortical sectors were 'silenced' by median nerve transection. (2) Significant inputs restricted to the dorsum of the radial hand and the dorsum of digits 1, 2 and 3 were immediately 'unmasked' by median nerve transection. (3) These immediately 'unmasked' regions were topographically crude, and represented only fragments of this dorsal skin. They were transformed, over time, into very large, highly topographic and complete representations of dorsal skin surfaces. (4) Representations of bordering glabrous skin surfaces progressively expanded to occupy larger and larger portions of the former median nerve cortical representational zone. (5) These 'expanded' representations of ulnar nerve-innervated skin surfaces sometimes moved, in entirety, into the former median nerve representational zone. (6) Almost all of the former median nerve zone was driven by new inputs in a map derived 22 days after nerve section. At shorter times (3, 6 and 11 days), 'reoccupation' was still incomplete. (7) Very significant changes in map dimensions within and outside of the former median skin cortical field were seen after the 'reoccupation' of the deprived cortex by 'new' inputs was initially completed. (8) Progressive changes were recorded within the original ulnar and radial nerve cortical representational zones, as skin surfaces originally overtly represented wholly within these regions expanded into the former median nerve zone. (9) Throughout the studied period, the cortical representational loci of many skin sites appeared to change continually and often markedly. (10) The locations of map discontinuities also shifted significantly over time. (11) Concomitant with changes in representational magnification over time, inverse changes in receptive field sizes were recorded.(ABSTRACT TRUNCATED AT 400 WORDS)

Rapid changes in brainstem maps of adult primates after peripheral injury.

Cerebral cortical maps in adult primates reorganize within minutes-hours after peripheral injuries, but subcortical versus intracortical contributions to this rapid reorganization remain controversial. The present results show that injury of nerves to the hands of adult monkeys triggers rapid (minutes-hours) changes in maps of the hand in the brainstem main cuneate nucleus. These findings suggest that peripheral injury causes an initial concurrent reorganization of brainstem and cortical substrates and that early sensory changes emerge from reorganization involving multiple central levels.

Parcellated organization in the trigeminal and dorsal column nuclei of primates.

The subdivisions of the brainstem trigeminal complex in non-primate mammals are characterized by aggregated or parcellated patterns of neural organization. The present studies used cytochrome oxidase histochemistry to test if parcellated organization patterns also occur in the brainstems of primates. The results demonstrate that a parcellated pattern of neural organization exists in the trigeminal nucleus principalis, but not in the spinal trigeminal nuclei, of macaque and squirrel monkeys. The results further suggest that parcellation in the nucleus principalis qualitatively resembles the aggregated organization in dorsal column nuclei. Taken together with previous findings from non-primates, these results indicate that central parcellation is an organizational feature of specific ascending somatosensory projections in many mammals including primates.

Long-term cortical consequences of reinnervation errors after nerve regeneration in monkeys.

Sensory innervation patterns are commonly altered after nerve regeneration, but the long-term consequences of these peripheral changes on the central nervous system are not understood. We report here that when innervation patterns to the hands of two adult monkeys were changed by cross-repair of nerves, topographical features that were clearly related to the new innervation pattern remained apparent in primary somatosensory cortical area 3b as long as 2.9 years after repair. These findings indicate that peripheral innervation changes are not easily corrected by central circuits leading to primary cortex.

Current hypotheses of structural pattern formation in the somatosensory system and their potential relevance to humans.

Current hypotheses of structural pattern formation in the mammalian somatosensory system are modeled on experimental findings from the trigeminal system of rodents. The present results show that, like rodents, the trigeminal nucleus principalis of humans contains a parcellated pattern of cytochrome oxidase dense patches. These results provide an indication of the potential usefulness of rodent-based hypotheses for understanding pattern formation in human somatosensory connections.

The somatotopic pattern of afferent projections from the digits to the spinal cord and cuneate nucleus in macaque monkeys.

The somatotopic patterns of terminations in the spinal cord and cuneate nucleus of afferents from the digits of macaque monkeys were determined by the transganglionic transport of a mixture of wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) and free horseradish peroxidase (HRP). Injections placed in either a single digit or in various combinations of digits indicate that terminations from the digits are located medially in the superficial laminae of cervical segments 5-7 in the dorsal horn. Each digit has a distinct zone of terminations, and inputs from D1-D5 terminate in order in a rostrocaudal sequence. In the cuneate nucleus, afferents from single digits are ventrally situated and organized into rostrocaudally elongated columns of label. In the pars rotunda of the cuneate nucleus, the representations of the digits appear to be offset from one another with D1 represented most laterally, and the other digits represented in order progressively more medially. In portions of the cuneate nucleus rostral and caudal to the pars rotunda, the projections from the digits are more diffuse and overlap one another.

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.