Neeraj Jain

Bio: Neeraj Jain is an academic researcher from National Brain Research Centre. The author has contributed to research in topics: Somatosensory system & Cortex (anatomy). The author has an hindex of 26, co-authored 51 publications receiving 2271 citations. Previous affiliations of Neeraj Jain include Indian Institute of Technology, Jodhpur & University of Maryland, Baltimore.

Overlapping representations of the neck and whiskers in the rat motor cortex revealed by mapping at different anaesthetic depths

Abstract: The primary motor cortex of mammals has an orderly representation of different body parts Within the representation of each body part the organization is more complex, with groups of neurons representing movements of a muscle or a group of muscles In rats, uncertainties continue to exist regarding organization of the primary motor cortex in the whisker and the neck region Using intracortical microstimulation (ICMS) we show that movements evoked in the whisker and the neck region of the rat motor cortex are highly sensitive to the depth of anaesthesia At light anaesthetic depth, whisker movements are readily evoked from a large medial region of the motor cortex Lateral to this is a small region where movements of the neck are evoked However, in animals under deep anaesthesia whisker movements cannot be evoked Instead, neck movements are evoked from this region The neck movement region thus becomes greatly expanded An analysis of the threshold currents required to evoke movements at different anaesthetic depths reveals that the caudal portion of the whisker region has dual representation, of both the whisker and the neck movements The results also underline the importance of carefully controlling the depth of anaesthesia during ICMS experiments

Cortical connections of striate and extrastriate visual areas in tree shrews

Abstract: The ipsilateral and contralateral cortical connections of visual cortex of tree shrews (Tupaia belangeri) were investigated by placing restricted injections of fluorochrome tracers, wheat germ agglutinin-horseradish peroxidase, or biotinylated dextran amine into area 17 (V1), area 18 (V2), or the adjoining temporal dorsal area (TD). As previously reported, V1 was characterized by a widespread, patchy pattern of intrinsic connections; ipsilateral connections with V2, TD, and to a lesser extent, other areas of the temporal cortex; and contralateral connections with V1, V2, and TD. A surface-view of the myelin pattern in V1 revealed a patchwork of light and dark module-like regions. The ipsilateral connections with V2 and TD were roughly topographic, whereas heterotopic locations in V1 were callosally connected. Injections in V2 labeled as much as one third of V2 in a patchy pattern, and portions of ipsilateral V1 and TD in roughly topographic patterns. In addition, connections with several other visual areas in the temporal lobe were revealed. Contralaterally, most of the label was in V2, with some in V1 and TD. Injections in TD demonstrated connections within the region, and with adjoining portions of the temporal cortex, V2, and V1. There were sparse connections with an oval of densely myelinated cortex, which we have termed the temporal inferior area (TI). Callosal connections were concentrated in TD, but also included V2. The results provide further evidence for modular organizations within V1 and V2, and reveal for the first time the complete patterns of cortical connections of V2 and TD. The results are consistent with the proposal that at least three visual areas, the temporal anterior area, TA, the temporal dorsal area, TD, and the temporal posterior area, TP, exist along the rostrolateral border of V2 in tree shrews; suggest visual involvement of at least three other areas, the temporal inferior area, TI, the temporal anterior lateral area, and the temporal posterior inferior area located more ventrally in the temporal cortex; and fortify the conclusion that TD is the likely homologue of the middle temporal visual area of primates. Because tree shrews are considered close relatives of primates, the evidence for several visual areas along the border of V2 is more compatible with theories that propose a series of visual areas along V2 in primates, rather than a single visual area, V3.

Limits on plasticity in somatosensory cortex of adult rats: hindlimb cortex is not reactivated after dorsal column section.

Abstract: 1. To better understand the limits and extents of plasticity in sensory systems of adult mammals, we unilaterally sectioned the dorsal funiculus at thoracic levels in nine adult rats to deactivate ascending afferents from the hindpaw and lower body. After postsurgical recovery periods of 3 h to 3 mo, the region of primary somatosensory cortex (S1) representing the limbs and trunk was extensively mapped with microelectrodes. 2. Recording sites were later identified as being within the hindlimb representation and other parts of S1 by relating locations of microlesions to the cytochrome oxidase pattern in sections of cortex cut tangential to the pial surface. The extent and effectiveness of spinal cord lesions were evaluated by injecting cholera toxin B subunit conjugated with horseradish peroxidase (B-HRP) at various sites in the deafferented hindpaw. 3. In five animals with complete section of the dorsal funiculus, we failed to detect any response to cutaneous stimulation of any part of the body in the deafferented hindlimb cortex. In four other animals with incomplete lesions, neurons in some penetrations could be activated by hindlimb stimulation, but not by stimulating other body parts. In those cases without activation of hindlimb cortex, B-HRP was detected in the spinal cord only caudal to the lesion, and it was not transported to the nucleus gracilis. Limited transport past the lesion to nucleus gracilis was detected in cases with incomplete lesions. 4. The results indicate that forelimb inputs do not substitute for missing hindlimb inputs in primary somatosensory cortex in rats and that the potential for somatotopic reorganization is more limited than previously thought.

Short communication Multiple divisions of macaque precentral motor cortex identified with neurofilament antibody SMI-32

Abstract: In brain sections stained with monoclonal antibody SMI-32, which recognizes non-phosphorylated neurofilament protein, wedistinguished separate caudal, intermediate, and rostral subdivisions of gigantocellular precentral cortex areas 4c, 4i, and 4r in macaque.monkeys. The divisions form bands extending mediolaterally across the major body-region representations of the primary motor cortex.M1 . These observations provide additional evidence that primary motor cortex is not a single, structurally homogeneous cortical area.q1997 Elsevier Science B.V. Keywords: Primate; Monkey; Primary motor cortex; Premotor cortex; Immunocytochemistry; Architectonics The posterior portion of precentral cortex in humansand other primates is remarkable for its giant layer Vpyramidal cells Betz cells . This gigantocellular region,.usually denoted as area 4 after the work of Brodmann 1 ,wxcorresponds at least approximately to the primary motorarea M1 identified in electrical-stimulation studies.wx8,9,11,20,22–24,27 . Recent anatomical and physiologicalstudies suggest that M1 may be composed of separatecaudal and rostral subdivisions 10,12,22,24,25 . Thesewxreports are not entirely consistent, however: some studiesindicate that the rostral division has larger pyramidal cellsin layer V 25 or layer III 10 than the caudal division,wx wxwhile others indicate that the rostral part of M1 hassomewhat smaller layer V pyramidal cells than the caudalpart 22,24 .wxIn order to investigate further the possibility that area 4.M1 consists of multiple subdivisions, we examined theprecentral cortex of macaque monkeys using the mono-clonal antibody SMI-32, which recognizes primarily theheavy neurofilament subunit in its non-phosphorylated state

Critical periods of vulnerability for the developing nervous system: evidence from humans and animal models.

Abstract: Vulnerable periods during the development of the nervous system are sensitive to environmental insults because they are dependent on the temporal and regional emergence of critical developmental processes (i.e., proliferation, migration, differentiation, synaptogenesis, myelination, and apoptosis). Evidence from numerous sources demonstrates that neural development extends from the embryonic period through adolescence. In general, the sequence of events is comparable among species, although the time scales are considerably different. Developmental exposure of animals or humans to numerous agents (e.g., X-ray irradiation, methylazoxymethanol, ethanol, lead, methyl mercury, or chlorpyrifos) demonstrates that interference with one or more of these developmental processes can lead to developmental neurotoxicity. Different behavioral domains (e.g., sensory, motor, and various cognitive functions) are subserved by different brain areas. Although there are important differences between the rodent and human brain, analogous structures can be identified. Moreover, the ontogeny of specific behaviors can be used to draw inferences regarding the maturation of specific brain structures or neural circuits in rodents and primates, including humans. Furthermore, various clinical disorders in humans (e.g., schizophrenia, dyslexia, epilepsy, and autism) may also be the result of interference with normal ontogeny of developmental processes in the nervous system. Of critical concern is the possibility that developmental exposure to neurotoxicants may result in an acceleration of age-related decline in function. This concern is compounded by the fact that developmental neurotoxicity that results in small effects can have a profound societal impact when amortized across the entire population and across the life span of humans.

Treatment-Induced Cortical Reorganization After Stroke in Humans

Abstract: Background and Purpose—Injury-induced cortical reorganization is a widely recognized phenomenon. In contrast, there is almost no information on treatment-induced plastic changes in the human brain. The aim of the present study was to evaluate reorganization in the motor cortex of stroke patients that was induced with an efficacious rehabilitation treatment. Methods—We used focal transcranial magnetic stimulation to map the cortical motor output area of a hand muscle on both sides in 13 stroke patients in the chronic stage of their illness before and after a 12-day-period of constraint-induced movement therapy. Results—Before treatment, the cortical representation area of the affected hand muscle was significantly smaller than the contralateral side. After treatment, the muscle output area size in the affected hemisphere was significantly enlarged, corresponding to a greatly improved motor performance of the paretic limb. Shifts of the center of the output map in the affected hemisphere suggested the recru...

Plasticity and primary motor cortex.

Abstract: One fundamental function of primary motor cortex (MI) is to control voluntary movements. Recent evidence suggests that this role emerges from distributed networks rather than discrete representations and that in adult mammals these networks are capable of modification. Neuronal recordings and activation patterns revealed with neuroimaging methods have shown considerable plasticity of MI representations and cell properties following pathological or traumatic changes and in relation to everyday experience, including motor-skill learning and cognitive motor actions. The intrinsic horizontal neuronal connections in MI are a strong candidate substrate for map reorganization: They interconnect large regions of MI, they show activity-dependent plasticity, and they modify in association with skill learning. These findings suggest that MI cortex is not simply a static motor control structure. It also contains a dynamic substrate that participates in motor learning and possibly in cognitive events as well.

The injured spinal cord spontaneously forms a new intraspinal circuit in adult rats.

Abstract: In contrast to peripheral nerves, central axons do not regenerate. Partial injuries to the spinal cord, however, are followed by functional recovery. We investigated the anatomical basis of this recovery and found that after incomplete spinal cord injury in rats, transected hindlimb corticospinal tract (CST) axons sprouted into the cervical gray matter to contact short and long propriospinal neurons (PSNs). Over 12 weeks, contacts with long PSNs that bridged the lesion were maintained, whereas contacts with short PSNs that did not bridge the lesion were lost. In turn, long PSNs arborize on lumbar motor neurons, creating a new intraspinal circuit relaying cortical input to its original spinal targets. We confirmed the functionality of this circuit by electrophysiological and behavioral testing before and after CST re-lesion. Retrograde transynaptic tracing confirmed its integrity, and revealed changes of cortical representation. Hence, after incomplete spinal cord injury, spontaneous extensive remodeling occurs, based on axonal sprout formation and removal. Such remodeling may be crucial for rehabilitation in humans.