Areal Distributions of Cortical Neurons Projecting to Different Levels of the Caudal Brain Stem and Spinal Cord in Rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Ag_m), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb.

The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI. Injections in lateral SI representing the face produced dense terminal label in the contralateral trigeminal complex. Injections in cortex devoted to the forelimb and forepaw labeled the contralateral cuneate nucleus and parts of the dorsal horn of the spinal cord. The cortical injections also demonstrated interconnections of parts of SI with some of the other regions of cortex with projections to the spinal cord, and provided further evidence for the existence of PV in rats.     

An examination of somatosensory area SIII in ferret cortex

A somatotopically organized region on the suprasylvian gyrus of the ferret was examined using multiunit recordings and anatomical tracer injections. This area, which contains a representation of the face, was bordered by the primary somatosensory area (SI), anteriorly, and by the visually responsive rostral posterior parietal cortex (PPr), posteriorly. Anatomical tracers revealed connections to this region from cortical areas MI, SI, MRSS, PPr, and the thalamic posterior nucleus. These results are consistent with previous work in ferrets as well as with the location, physiology, and connectivity of area SIII in cats. Given its associations, functional properties, location, and homology, it is proposed that this region represents the third cortical somatosensory area (SIII) in ferrets.     

Areal distributions of cortical neurons projecting to different levels of the caudal brain stem and spinal cord in rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Agm), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb. The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI.(ABSTRACT TRUNCATED AT 400 WORDS)     

Multiple Representations of the Body and Input-Output Relationships in the Agranular and Granular Cortex of the Chronic Awake Guinea Pig

The organization of somatosensory input and the input-output relationships in regions of the agranular frontal cortex (AGr) and granular parietal cortex (Gr) were examined in the chronic awake guinea pig, using the combined technique of single-unit recording and intracortical microstimulation (ICMS). AGr, which was cytoarchitectonically subdivided into medial (AGrm) and lateral (AGrl) parts, also can be characterized on a functional basis. AGrl contains the head, forelimb, and most hindlimb representations; only a small number of hindlimb neurons are confined in AGrm. Different distributions of submodalities exist in AGr and Gr: AGr receives predominantly deep input (with the exception of the vibrissa region, which receives cutaneous input), whereas neurons of Gr respond almost exclusively to cutaneous input. The cutaneous or deep receptive field (RF) of each neuron was determined by natural peripheral stimulation. All studied neurons were activated by small RFs, with the exception of lip, nose, pinna, and limb units of lateral Gr (Grl), for which the RFs were larger.

Microelectrode mapping experiments revealed the existence of three spatially separate, incomplete body maps in which somatosensory and motor representations overlap. One body map, with limbs medially and head rostrolaterally, is contained in AGr. A second map, comparable to the first somatosensory cortex (SI) of other mammals, is found in Gr, with hindlimb, trunk, forelimb, and head representations in an orderly mediolateral sequence. An unresponsive zone separates the head area from the forelimb region. A third map, with the forelimb rostrally and the hindlimb caudally, lies adjacent and lateral to the SI head area. This limb representation, which is characterized by an upright and small size compared to that found in SI, can be considered to be part of the second somatosensory cortex (SII). A distinct head representation was not recognized as properly belonging to SII, but the evidence that neurons of the SI head region respond to stimulation of large RFs located in lips, nose, and pinna leads us to hypothesize that the SII face area overlaps that of SI to some extent, or, alternatively, that the two areas are strictly contiguous and the limits are ambiguous, making them difficult to distinguish.

The input-output relationships were based on the results of RF mapping and ICMS in the same electrode penetration. The intrinsic specific interconnections of cortical neurons whose afferent input and motor output is related to identical body regions show a considerable degree of refinement. The input-output correspondence is especially pronounced for neurons with small RFs. This study confirms and extends similar data recently reported for other rodents.     

Topical organization of somatic projections in the fur seal cerebral cortex

To map somatic projections in the cerebral cortex of the fur sealCallorhinus ursinus multiple spike activity of cortical neurons evoked by tactile stimulation of different parts of the body surface was recorded in acute experiments. The region of somatic representation is bounded rostrally by the postcruciate and coronal sulci, caudally by the anterior suprasylvian sulcus, and dorsomedially by the ansate sulcus. The somatotopic map is oriented so that the projection of the head faces ventrolaterally, and that of the caudal part of the trunk faces dorsomedially; the projection region of the forelimb is buried in the coronal sulcus. The projection area of the head occupies the greatest area, and in it, the greatest area is occupied by the region of the superior labial vibrissae.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 344–351, May–June, 1985.     

A Comparison of the Ipsilateral Cortical Projections to the Dorsal and Ventral Subdivisions of the Macaque Premotor Cortex

The cortical connections of the dorsal (PMd) and ventral (PMv) subdivisions of the premotor area (PM, lateral area 6) were studied in four monkeys (Macaca fascicularis) through the use of retrograde tracers. In two animals, tracer was injected ventral to the arcuate sulcus (PMv), in a region from which forelimb movements could be elicited by intracortical microstimulation (ICMS). Tracer injections dorsal to the arcuate sulcus (PMd) were made in two locations. In one animal, tracer was injected caudal to the genu of the arcuate sulcus (in caudal PMd [cPMd], where ICMS was effective in eliciting forelimb movements); in another animal, it was injected rostral to the genu of the arcuate sulcus (in rostral PMd [rPMd], where ICMS was ineffective in eliciting movements). Retrogradely labeled neurons were counted in the ipsilateral hemisphere and located in cytoarchitectonically identified areas of the frontal and parietal lobes. Although both PMv and PMd were found to receive inputs from other motor areas, the prefrontal cortex, and the parietal cortex, there were differences in the topography and the relative strength of projections from these areas.

There were few common inputs to PMv and PMd; only the supplementary eye fields projected to all three areas studied. Interconnections within PMd or PMv appeared to link hindlimb and forelimb representations, and forelimb and face representations; however, connections between PMd and PMv were sparse. Areas cPMd and PMv were found to receive inputs from other motor areas—the primary motor area, the supplementary motor area, and the cingulate motor area—but the topography and strength of projections from these areas varied. Area rPMd was found to receive sparse inputs, if any, from these motor areas. The frontal eye field (area 8a) was found to project to PMv and rPMd, and area 46 was labeled substantially only from rPMd. Parietal projections to PMv were found to originate from a variety of somatosensory and visual areas, including the second somatosensory cortex and related areas in the parietal operculum of the lateral sulcus, as well as areas 5, 7a, and 7b, and the anterior intraparietal area. By contrast, projections to cPMd arose only from area 5. Visual areas 7m and the medial intraparietal area were labeled from rPMd. Relatively more parietal neurons were labeled after tracer injections in PMv than in PMd. Thus, PMv and PMd appear to be parts of separate, parallel networks for movement control.     

Cytoarchitecture of the Ferret Suprasylvian Gyrus Correlated with Areas Containing Multiunit Responses Elicited by Stimulation of the Face

The cytoarchitecture was studied in a segment of the ferret suprasylvian gyrus containing at least two and possibly four somesthetic representations of the face that were observed in the primary somatosensory cortex. These representations were restricted to the crown of the gyrus and were surrounded by somesthetically unresponsive cortex that extended down both sides to the base of adjacent sulci. Numerous cytoarchitectonic subdivisions were found on a qualitative basis, and were confirmed quantitatively by cluster analyses and relevant statistical tests of 10 prominent features from layers III, IV, and V. Four distinct cytoarchitectonic subdivisions, each with a well-developed and homogeneous granular layer IV, were found distributed from anterior to posterior along the crown of the gyrus at sites corresponding to the locations of the four facial representations. The surrounding unresponsive cortex had a fragmented cytoarchitecture, especially along the medial bank and base of the coronal sulcus. This unresponsive cortex separated the facial representations from the body representations, which were located on the adjacent posterior cruciate gyrus. Most of the unresponsive subdivisions had a heterogeneous or agranular layer IV and fairly well-developed sublamination in layer III, which may be indicative of extensive corticocortical connections. One set of unresponsive subdivisions had comparable cytoarchitectures that directly bordered the facial representations. Another set of unresponsive subdivisions with comparable architectures occupied most of the lateral bank of the gyrus. The implications of multiple representations and cytoarchitectonic fragmentation of the ferret primary somatosensory cortex are discussed in relation to the organization of the primary somatosensory cortex in other species.     

Cortical organization in moles: evidence of new areas and a specialized S2

The somatosensory cortex of several mole species (family Talpidae), with different peripheral sensory adaptations, was investigated and compared to determine common and specialized features of cortical organization. Previously unidentified medial representations of the trunk and limbs were found in all species, indicating that S1 in moles occupies a medial to lateral strip of cortex as in most other mammals. This finding suggests a large lateral forelimb representation, previously attributed to S1, is actually part of S2. In the face representation, evidence was found for three representations of the unusual nose of the star-nosed mole ( Condylura cristata ). Each of these areas was divided into a series of modules (visible in cytochrome oxidase processed tissue) representing individual nasal appendages on the star. In the closely related but less specialized eastern mole ( Scalopus aquaticus ) and coast mole ( Scapanus orarius ), only two nose representations were identified in an area of cortex with a more uniform histological appearance. The results indicate that moles have enlarged somatosensory representations of the glabrous nose as compared to shrews and rats that instead have large vibrissal representations. In addition moles have a very large and specialized representation of the digging forepaw in S2. Since this part of S2 projects directly to the cervical spinal cord, the specialization may provide adaptive sensorimotor functions related to digging.     

Cortical-organization in moles: evidence of new areas and a specialized S2

The somatosensory cortex of several mole species (family Talpidae), with different peripheral sensory adaptations, was investigated and compared to determine common and specialized features of cortical organization. Previously unidentified medial representations of the trunk and limbs were found in all species, indicating that S1 in moles occupies a medial to lateral strip of cortex as in most other mammals. This finding suggests a large lateral forelimb representation, previously attributed to S1, is actually part of S2. In the face representation, evidence was found for three representations of the unusual nose of the star-nosed mole (Condylura cristata). Each of these areas was divided into a series of modules (visible in cytochrome oxidase processed tissue) representing individual nasal appendages on the star. In the closely related but less specialized eastern mole (Scalopus aquaticus) and coast mole (Scapanus orarius), only two nose representations were identified in an area of cortex with a more uniform histological appearance. The results indicate that moles have enlarged somatosensory representations of the glabrous nose as compared to shrews and rats that instead have large vibrissal representations. In addition moles have a very large and specialized representation of the digging forepaw in S2. Since this part of S2 projects directly to the cervical spinal cord, the specialization may provide adaptive sensorimotor functions related to digging.     

The organization and connections of somatosensory cortex in the brush-tailed possum (Trichosurus vulpecula): evidence for multiple, topographically organized and interconnected representations in an Australian marsupial

Microelectrode mapping techniques were used to determine the organization of somatosensory cortex in the Australian brush-tailed possum (Trichosurus vulpecula). The results of electrophysiological mapping were combined with data on the cyto- and myeloarchitecture, and patterns of corticocortical connections, using sections cut tangential to the pial surface. We found evidence for three topographically organized representations of the body surface that were coextensive with architectonic subdivisions. A large, discontinuous cutaneous representation in anterior parietal cortex was termed the primary somatosensory area (SI). Lateral to SI we found evidence for two further areas, the second somatosensory area (SII) and the parietal ventral area (PV). While neurones in all of these areas were responsive to cutaneous stimulation, those of SI were non-habituating, whereas those in SII and PV often habituated to the stimuli. Moreover, neuronal receptive fields in SII and PV were, in general, larger than those in SI. Neurones in cortex adjacent to the rostral and caudal boundaries of SI, including cortex that interdigitated between the discontinuous SI head and body representations, required stimulation of deep receptors in the periphery to elicit responses. Within the region of cortex containing neurones responsive to stimulation of deep receptors, body parts were represented in a mediolateral progression. Injections of anatomical tracers placed in electrophysiologically identified locations in SI revealed ipsilateral connections with other parts of SI, as well as cortex rostral to, caudal to, and interdigitating between, SI. Injections in SI also resulted in labelling in PV, SII, motor cortex, posterior parietal cortex and perirhinal cortex. The patterns of contralateral projections reflected those of ipsilateral projections, although they were relatively less dense. The present findings support recent observations in other marsupials in which multiple representations of the body surface were described, and suggest that multiple interconnected sensory representations may be a common feature of cortical organization and function in marsupials.     

Deficits and recovery of body stabilization during acrobatic locomotion after focal lesion to the somatosensory cortex: a kinematic analysis combined with cortical mapping

We used a kinematic analysis for assessing locomotor impairments and evaluating the time course of recovery after focal injury to the forepaw area of the primary somatosensory cortex (SI) in rats. The animals were trained to traverse a beam that was rotated at various speeds. Changes in orientation of the body and independent movement of the anterior and posterior parts of the body were reconstructed using a 3D motion analysis. In addition, we used electrophysiological cortical mapping to search for neurophysiological changes within the spared cortical zones surrounding the lesion. Neuronal recordings were performed in the same animals prior to and 3 weeks after the lesion induction. Our findings show that a focal lesion that destroyed about 60% of the forepaw representational zone was sufficient to cause conspicuous impairments in the rats' ability to produce adequate motor adjustments to compensate for the lateral shift of the beam and to avoid falling. The main deficits were reflected in a lack of appropriate coordination between the anterior and posterior parts of the body and an inability to maintain a regular gait during locomotion. Skilled locomotion was fully recovered within a 2-3 week period. Functional recovery cannot be ascribed to a restitution of the lost sensory representations. A permanent decrease of forepaw representation was recorded despite the re-emergence of restricted representational sectors in the peri-lesion zone. We suggest that alterations may have occurred in other cortical and subcortical areas interconnected with the injured area. It is also conceivable that the functional recovery involved an increased reliance on all the available sources of sensorimotor regulation as well as the use of behavioral strategies.     

Organization of cortical processing for facial movements during licking in cats

We proposed that cortical organization for the execution of adequate licking in cats was processed under the control of two kinds of affiliated groups for face and jaw & tongue movements (Hiraba H, Sato T. 2005A. Cerebral control of face, jaw, and tongue movements in awake cats: Changes in regional cerebral blood flow during lateral feeding Somatosens Mot Res 22:307-317). We assumed the cortical organization for face movements from changes in MRN (mastication-related neuron) activities recorded at area M (motor cortex) and orofacial behaviors after the lesion in the facial SI (facial region in the primary somatosensory cortex). Although we showed the relationship between facial SI (area 3b) and area M (area 4delta), the property of area C (area 3a) was not fully described. The aim of this present study is to investigate the functional role of area C (the anterior part of the coronal sulcus) that transfers somatosensory information in facial SI to area M, as shown in a previous paper (Hiraba H. 2004. The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats Somatosens Mot Res 21:87-97). We examined the properties of MRNs in area C and changes in orofacial behaviors after the area C or area M lesion. MRNs in area C had in common RFs in the lingual, perioral, and mandibular parts, and activity patterns of MRNs showed both post- and pre-movement types. Furthermore, cats with the area C lesion showed similar disorders to cats with the area M lesion, such as the dropping of food from the contralateral mouth, prolongation of the period of ingestion and mastication, and so on. From these results, we believe firmly the organization of unilateral cortical processing in facial SI, area C, and area M for face movements during licking.     

Organization of cortical processing for facial movements during licking in cats

We proposed that cortical organization for the execution of adequate licking in cats was processed under the control of two kinds of affiliated groups for face and jaw & tongue movements (Hiraba H, Sato T. 2005A. Cerebral control of face, jaw, and tongue movements in awake cats: Changes in regional cerebral blood flow during lateral feeding Somatosens Mot Res 22:307–317). We assumed the cortical organization for face movements from changes in MRN (mastication-related neuron) activities recorded at area M (motor cortex) and orofacial behaviors after the lesion in the facial SI (facial region in the primary somatosensory cortex). Although we showed the relationship between facial SI (area 3b) and area M (area 4δ), the property of area C (area 3a) was not fully described. The aim of this present study is to investigate the functional role of area C (the anterior part of the coronal sulcus) that transfers somatosensory information in facial SI to area M, as shown in a previous paper (Hiraba H. 2004. The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats Somatosens Mot Res 21:87--97). We examined the properties of MRNs in area C and changes in orofacial behaviors after the area C or area M lesion. MRNs in area C had in common RFs in the lingual, perioral, and mandibular parts, and activity patterns of MRNs showed both post- and pre-movement types. Furthermore, cats with the area C lesion showed similar disorders to cats with the area M lesion, such as the dropping of food from the contralateral mouth, prolongation of the period of ingestion and mastication, and so on. From these results, we believe firmly the organization of unilateral cortical processing in facial SI, area C, and area M for face movements during licking.     

The organization of somatosensory cortex in the short-tailed opossum ( Monodelphis domestica )

The organization of neocortex in the short-tailed opossum ( Monodelphis domestica ) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.     

The organization of somatosensory cortex in the short-tailed opossum (Monodelphis domestica)

The organization of neocortex in the short-tailed opossum (Monodelphis domestica) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.     

Experience-induced plasticity of cutaneous maps in the primary somatosensory cortex of adult monkeys and rats

In a first study, the representations of skin surfaces of the hand in the primary somatosensory cortex, area 3b, were reconstructed in owl monkeys and squirrel monkeys trained to pick up food pellets from small, shallow wells, a task which required skilled use of the digits. Training sessions included limited manual exercise over a total period of a few hours of practice. From an early clumsy performance in which many retrieval attempts were required for each successful pellet retrieval, the monkeys exhibited a gradual improvement. Typically, the animals used various combinations of digits before developing a successful retrieval strategy. As the behavior came to be stereotyped, monkeys consistently engaged surfaces of the distal phalanges of one or two digits in the palpation and capture of food pellets from the smallest wells. Microelectrode mapping of the hand surfaces revealed that the glabrous skin of the fingertips predominantly involved in the dexterity task was represented over topographically expanded cortical sectors. Furthermore, cutaneous receptive fields which covered the most frequently stimulated digital tip surfaces were less than half as large as were those representing the corresponding surfaces of control digits. In a second series of experiments, Long-Evans rats were assigned to environments promoting differential tactile experience (standard, enriched, and impoverished) for 80 to 115 days from the time of weaning. A fourth group of young adult rat experienced a severe restriction of forepaw exploratory movement for either 7 or 15 days. Cortical maps derived in the primary somatosensory cortex showed that environmental enrichment induced a substantial enlargement of the cutaneous forepaw representation, and improved its spatial resolution (smaller glabrous receptive fields). In contrast, tactile impoverishment resulted in a degradation of the forepaw representation that was characterized by larger cutaneous receptive fields and the emergence of non-cutaneous responses. Cortical maps derived in the hemispheres contralateral to the immobilized forelimb exhibited a severe decrease of about 50% in the overall areal extent of the cutaneous representation of the forepaw, which resulted from the invasion of topographically organized cortical zones of non-cutaneous responses, and numerous discontinuities in the representation of contiguous skin territories. The size and the spatial arrangement of the cutaneous receptive fields were not significantly modified by the immobilization of the contralateral forelimb. Similar results were obtained regardless of whether the forelimb restriction lasted 7 or 15 days. These two studies corroborate the view that representational constructs are permanently reshaped by novel experiences through dynamic competitive processes. These studies also support the notion that subject-environment interactions play a crucial role in the maintenance of basic organizational features of somatosensory representations.     

Responsiveness of Reorganized Primary Somatosensory (SI) Cortex after Local Inactivation of Normal SI Cortex in Chronic Spinal Cats

The cortical map of adult cats that sustained spinal cord transection at T₁₂ when they were 2 weeks old is characterized by a clear duplication of the representation of the forelimb, rostral trunk, and neck. The novel representation is located in the cortical region that is, in nonoperated animals, normally devoted to the hindlimb representation. We have investigated the possibility that the reactivation of the deprived hindlimb cortex may be mediated by corticocortical projections from normal to reorganized cortex. The primary somatosensory (SI) cortex was initially mapped to determine the boundaries of the normal and reorganized cortical representations. Somatotopically corresponding regions in both normal and reorganized cortex representing the trunk, the web space, or the shoulder were more precisely mapped. Inactivation of normal cortex was achieved by the nanoinjection of a solution of lidocaine hydrochloride stained with Chicago sky blue. Two major findings are described. First, inactivation of a circumscribed region of normal cortex representing a given receptive field (RF) failed to reduce or inhibit the responsiveness of a somatotopically corresponding RF represented in reorganized cortex. Therefore, it is unlikely that intracortical connections between normal and reorganized cortex could account for the reorganizational processes observed in cats that sustained spinal cord transection at 2 weeks of age. Second, the chemical blockade of normal cortex provoked an increase of the responsiveness and of the size of the peripheral RFs represented in reorganized cortex. This finding suggests that there are corticocortical connections (possibly topographically organized) between normal and reorganized cortex, and that these connections are inhibitory.     

Responsiveness of reorganized primary somatosensory (SI) cortex after local inactivation of normal SI cortex in chronic spinal cats.

The cortical map of adult cats that sustained spinal cord transection at T12 when they were 2 weeks old is characterized by a clear duplication of the representation of the forelimb, rostral trunk, and neck. The novel representation is located in the cortical region that is, in nonoperated animals, normally devoted to the hindlimb representation. We have investigated the possibility that the reactivation of the deprived hindlimb cortex may be mediated by corticocortical projections from normal to reorganized cortex. The primary somatosensory (SI) cortex was initially mapped to determine the boundaries of the normal and reorganized cortical representations. Somatotopically corresponding regions in both normal and reorganized cortex representing the trunk, the web space, or the shoulder were more precisely mapped. Inactivation of normal cortex was achieved by the nanoinjection of a solution of lidocaine hydrochloride stained with Chicago sky blue. Two major findings are described. First, inactivation of a circumscribed region of normal cortex representing a given receptive field (RF) failed to reduce or inhibit the responsiveness of a somatotopically corresponding RF represented in reorganized cortex. Therefore, it is unlikely that intracortical connections between normal and reorganized cortex could account for the reorganizational processes observed in cats that sustained spinal cord transection at 2 weeks of age. Second, the chemical blockade of normal cortex provoked an increase of the responsiveness and of the size of the peripheral RFs represented in reorganized cortex. This finding suggests that there are corticocortical connections (possibly topographically organized) between normal and reorganized cortex, and that these connections are inhibitory.     

Decoding Face Information in Time,Frequency and Space from Direct Intracranial Recordings of the Human Brain

Faces are processed by a neural system with distributed anatomical components, but the roles of these components remain unclear. A dominant theory of face perception postulates independent representations of invariant aspects of faces (e.g., identity) in ventral temporal cortex including the fusiform gyrus, and changeable aspects of faces (e.g., emotion) in lateral temporal cortex including the superior temporal sulcus. Here we recorded neuronal activity directly from the cortical surface in 9 neurosurgical subjects undergoing epilepsy monitoring while they viewed static and dynamic facial expressions. Applying novel decoding analyses to the power spectrogram of electrocorticograms (ECoG) from over 100 contacts in ventral and lateral temporal cortex, we found better representation of both invariant and changeable aspects of faces in ventral than lateral temporal cortex. Critical information for discriminating faces from geometric patterns was carried by power modulations between 50 to 150 Hz. For both static and dynamic face stimuli, we obtained a higher decoding performance in ventral than lateral temporal cortex. For discriminating fearful from happy expressions, critical information was carried by power modulation between 60–150 Hz and below 30 Hz, and again better decoded in ventral than lateral temporal cortex. Task-relevant attention improved decoding accuracy more than10% across a wide frequency range in ventral but not at all in lateral temporal cortex. Spatial searchlight decoding showed that decoding performance was highest around the middle fusiform gyrus. Finally, we found that the right hemisphere, in general, showed superior decoding to the left hemisphere. Taken together, our results challenge the dominant model for independent face representation of invariant and changeable aspects: information about both face attributes was better decoded from a single region in the middle fusiform gyrus.