Prem Chand

Bio: Prem Chand is an academic researcher from National Brain Research Centre. The author has contributed to research in topics: Cuneate nucleus & Spinal cord. The author has an hindex of 6, co-authored 8 publications receiving 176 citations. Previous affiliations of Prem Chand include Allahabad University.

Large-scale reorganization of the somatosensory cortex following spinal cord injuries is due to brainstem plasticity

Abstract: Adult mammalian brains undergo reorganization following deafferentations due to peripheral nerve, cortical or spinal cord injuries. The largest extent of cortical reorganization is seen in area 3b of the somatosensory cortex of monkeys with chronic transection of the dorsal roots or dorsal columns of the spinal cord. These injuries cause expansion of intact face inputs into the deafferented hand cortex, resulting in a change of representational boundaries by more than 7 mm. Here we show that large-scale reorganization in area 3b following spinal cord injuries is due to changes at the level of the brainstem nuclei and not due to cortical mechanisms. Selective inactivation of the reorganized cuneate nucleus of the brainstem eliminates observed face expansion in area 3b. Thus, the substrate for the observed expanded face representation in area 3b lies in the cuneate nucleus.

Intracortical and Thalamocortical Connections of the Hand and Face Representations in Somatosensory Area 3b of Macaque Monkeys and Effects of Chronic Spinal Cord Injuries.

Abstract: Brains of adult monkeys with chronic lesions of dorsal columns of spinal cord at cervical levels undergo large-scale reorganization. Reorganization results in expansion of intact chin inputs, which reactivate neurons in the deafferented hand representation in the primary somatosensory cortex (area 3b), ventroposterior nucleus of the thalamus and cuneate nucleus of the brainstem. A likely contributing mechanism for this large-scale plasticity is sprouting of axons across the hand-face border. Here we determined whether such sprouting takes place in area 3b. We first determined the extent of intrinsic corticocortical connectivity between the hand and the face representations in normal area 3b. Small amounts of neuroanatomical tracers were injected in these representations close to the electrophysiologically determined hand-face border. Locations of the labeled neurons were mapped with respect to the detailed electrophysiological somatotopic maps and histologically determined hand-face border revealed in sections of the flattened cortex stained for myelin. Results show that intracortical projections across the hand-face border are few. In monkeys with chronic unilateral lesions of the dorsal columns and expanded chin representation, connections across the hand-face border were not different compared with normal monkeys. Thalamocortical connections from the hand and face representations in the ventroposterior nucleus to area 3b also remained unaltered after injury. The results show that sprouting of intrinsic connections in area 3b or the thalamocortical inputs does not contribute to large-scale cortical plasticity. Significance statement: Long-term injuries to dorsal spinal cord in adult primates result in large-scale somatotopic reorganization due to which chin inputs expand into the deafferented hand region. Reorganization takes place in multiple cortical areas, and thalamic and medullary nuclei. To what extent this brain reorganization due to dorsal column injuries is related to axonal sprouting is not known. Here we show that reorganization of primary somatosensory area 3b is not accompanied with either an increase in intrinsic cortical connections between the hand and face representations, or any change in thalamocortical inputs to these areas. Axonal sprouting that causes reorganization likely takes place at subthalamic levels.

Cytoarchitectonic organization and morphology of the cells of hippocampal complex in strawberry finch, Estrilda amandava.

Abstract: Neurons in the hippocampal complex (dorsomedial forebrain) were described and located following Golgi impregnation. Five fields were recognized in the hippocampal complex: medial and lateral hippocampus, parahippocampal area, central field of the parahippocampal area and crescent field. In the medial hippocampus three layers have been observed: suprapyramidal towards the pial surface, pyramidal at the central and infrapyramidal adjacent to the ventricle. Neurons of the hippocampal complex were classified in to two main cell groups: predominant projection neurons with spinous dendrites and local circuit neurons. Projection neurons were further sub classified into three main types: pyramidal, pyramidal like, and multipolar neurons. In addition to these neurons, monotufted and bitufted neurons were also observed in the medial and lateral hippocampus with low frequency. The pyramidal neurons were dominant neuronal types in the pyramidal layer-II of the medial hippocampus, mixed with pyramidal like and multipolar neurons. Pyramidal and pyramidal-like neurons were found restricted in the pyramidal layer II of the medial hippocampus while the multipolar neurons were uniformly distributed in all subfields of the hippocampal complex. In the lateral hippocampus irregular shaped radial glial cells were present near the ventricular wall and projecting their dendrites towards the pia. Second group of local circuit neurons with local arborization of their projections were present in the medial hippocampus and in parahippocampal area.

Cyto-architecture and neuronal types of the dorsomedial cerebral cortex of the common Indian wall lizard, Hemidactylus flaviviridis.

Abstract: A B s T r A c T The cyto-architecture and morphology of the neuronal types of the dorsomedial cortex of the lizard, Hemidactylus flaviviridis has been studied with the help of Cresyl violet staining and Golgi impregnation method. The dorsomedial cerebral cortex displayed three neuronal layers. Layer-I contains only few neuronal somas and also the dendrites ascending from the subjacent layers. Layer-II is characterized by two to three cell thick densely packed neuronal somas. Layer-III contains loosely packed neuronal somas and the dendrites and axon descending from layer-I and II. Below the layer-III an ependymal layer is observed just above the ventricle. Six classes of neurons were distinguished in the cellular layer of dorsomedial cortex of Hemidactylus flaviviridis: bitufted neurons, pyramidal neurons, inverted pyramidal neurons, bipyramidal neurons, multipolar neurons, and candelabra-like monotufted neurons. The pyramidal cells were large showing more or less single type present in the cellular layer. The multipolar neurons have mostly intracortical dendritic branching and connections. Bipyramidal neurons showed pyramidal appearance of their soma and send dendritic branches towards the superficial plexiform layer and deep plexiform layer. The candelabra-like monotufted neurons have very high dendritic branching. The comparison of the neuronal types of dorsomedial cortex of reptiles with the parahippocampal area of birds and CA3 region of mammalian hippocampus suggests possibility of their homology.

Neuronal classes in the corticoid complex of the telencephalon of the strawberry finch, Estrilda amandava

Abstract: The present study, based on neurohistological techniques (Nissl-staining, Golgi-impregnation), focuses on the cytoarchitecture of the corticoid complex in the strawberry finch, Estrilda amandava. This complex in birds occupies the dorsolateral surface of the telencephalic pallium and remains subdivided into an intermediate corticoid area (CI) and a dorsolateral corticoid area (CDL). The CDL in the strawberry finch is a thin superficial part of the caudal pallium adjoining the medially situated hippocampal formation, whereas the CI is demarcated between the CDL and the parahippocampal area of telencephalon. Neurons of the corticoid complex are classified into three main cell groups: predominant projection neurons, local circuit neurons and stellate neurons. The spinous projection neurons send out distant projecting axons that typically extend several varicose collaterals. Most of these collaterals lie parallel to the ventricle. These neurons are subclassified into pyramidal neurons (localized only in the CI) and multipolar neurons (present in both the CI and CDL). The CDL also possesses small and medium-sized horizontal cells, which are bitufted or multipolar with smooth, moderately branching dendrites. The aspinous local circuit neurons extend short axons that ramify locally. Stellate neurons have sparse spinous dendrites and locally arborizing axons. The corticoid complex of birds corresponds to the lateral cerebral cortex of lizards and to the entorhinal cortex of mammals on the basis of neuronal morphology and bidirectional connections between adjacent areas.

Forefront review what is the mammalian dentate gyrus good for

Abstract: In the mammalian hippocampus, the dentate gyrus (DG) is characterized by sparse and powerful unidirectional projections to CA3 pyramidal cells, the so-called mossy fi- bers (MF). The MF form a distinct type of synapses, rich in zinc, that appear to duplicate, in terms of the information they convey, what CA3 cells already receive from entorhinal cor- tex layer II cells, which project both to the DG and to CA3. Computational models have hypothesized that the function of the MF is to enforce a new, well-separated pattern of activity onto CA3 cells, to represent a new memory, prevail- ing over the interference produced by the traces of older memories already stored on CA3 recurrent collateral connec- tions. Although behavioral observations support the notion that the MF are crucial for decorrelating new memory repre- sentations from previous ones, a number of findings require that this view be reassessed and articulated more precisely in the spatial and temporal domains. First, neurophysiological recordings indicate that the very sparse dentate activity is concentrated on cells that display multiple but disorderly place fields, unlike both the single fields typical of CA3 and the multiple regular grid-aligned fields of medial entorhinal cortex. Second, neurogenesis is found to occur in the adult DG, leading to new cells that are functionally added to the existing circuitry, and may account for much of its ongoing activity. Third, a comparative analysis suggests that only mammals have evolved a DG, despite some of its features being present also in reptiles, whereas the avian hippocam- pus seems to have taken a different evolutionary path. Thus, we need to understand both how the mammalian dentate operates, in space and time, and whether evolution, in other vertebrate lineages, has offered alternative solutions to the same computational problems. © 2008 IBRO. Published by Elsevier Ltd. All rights reserved.

Is neuroplasticity in the central nervous system the missing link to our understanding of chronic musculoskeletal disorders

Abstract: Musculoskeletal rehabilitative care and research have traditionally been guided by a structural pathology paradigm and directed their resources towards the structural, functional, and biological abnormalities located locally within the musculoskeletal system to understand and treat Musculoskeletal Disorders (MSD) However the structural pathology model does not adequately explain many of the clinical and experimental findings in subjects with chronic MSD and, more importantly, treatment guided by this paradigm fails to effectively treat many of these conditions

Reassessing cortical reorganization in the primary sensorimotor cortex following arm amputation

Abstract: The role of cortical activity in generating and abolishing chronic pain is increasingly emphasized in the clinical community. Perhaps the most striking example of this is the maladaptive plasticity theory, according to which phantom pain arises from remapping of cortically neighbouring representations (lower face) into the territory of the missing hand following amputation. This theory has been extended to a wide range of chronic pain conditions, such as complex regional pain syndrome. Yet, despite its growing popularity, the evidence to support the maladaptive plasticity theory is largely based on correlations between pain ratings and oftentimes crude measurements of cortical reorganization, with little consideration of potential contributions of other clinical factors, such as adaptive behaviour, in driving the identified brain plasticity. Here, we used a physiologically meaningful measurement of cortical reorganization to reassess its relationship to phantom pain in upper limb amputees. We identified small yet consistent shifts in lip representation contralateral to the missing hand towards, but not invading, the hand area. However, we were unable to identify any statistical relationship between cortical reorganization and phantom sensations or pain either with this measurement or with the traditional Euclidian distance measurement. Instead, we demonstrate that other factors may contribute to the observed remapping. Further research that reassesses more broadly the relationship between cortical reorganization and chronic pain is warranted.