Showing papers by "Neeraj Jain published in 1997"

Deactivation and reactivation of somatosensory cortex after dorsal spinal cord injury

Abstract: Sensory stimuli to the body are conveyed by the spinal cord to the primary somatosensory cortex. It has long been thought that dorsal column afferents of the spinal cord represent the main pathway for these signals, but the physiological and behavioural consequences of cutting the dorsal column have been reported to range from mild and transitory to marked. We have re-examined this issue by sectioning the dorsal columns in the cervical region and recording the responses to hand stimulation in the contralateral primary somatosensory cortex (area 3b). Following a complete section of the dorsal columns, neurons in area 3b become immediately and perhaps permanently unresponsive to hand stimulation. Following a partial section, the remaining dorsal column afferents continue to activate neurons within their normal cortical target territories, but after five or more weeks the area of activation is greatly expanded. After prolonged recovery periods of six months or more, the deprived hand territory becomes responsive to inputs from the face (which are unaffected by spinal cord section). Thus, area 3b of somatosensory cortex is highly dependent on dorsal spinal column inputs, and other spinal pathways do not substitute for the dorsal columns even after injury.

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

REVIEW ■ : Reorganization of Sensory Systems of Primates after Injury:

Abstract: The orderly representations of sensory surfaces in the brains of adult mammals have the capacity to reor ganize after injuries that deprive these representations of some of their normal sources of activation. Such reorganizations can be produced by injury that occurs peripherally, such as nerve damage or amputation, or after injury to the CNS, such as spinal cord damage or cortical lesion. These changes likely are mediated by a number of different mechanisms, and can be extensive and involve the growth of new connections. Finally, some types of reorganizations may help mediate the recovery of lost functions, whereas others may lead to sensory abnormalities and perceptual errors. NEUROSCIENTIST 3:123-130, 1997