REVIEW ■ : Reorganization of Sensory Systems of Primates after Injury:
TL;DR: 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.
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
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TL;DR: Of critical concern is the possibility that developmental exposure to neurotoxicants may result in an acceleration of age-related decline in function, and 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.
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.
2,659 citations
TL;DR: This is the first demonstration in humans of a long-term alteration in brain function associated with a therapy-induced improvement in the rehabilitation of movement after neurological injury.
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...
1,390 citations
TL;DR: An animal model for investigating stimulus-induced rCBF responses in the rat is developed and it is shown that there is a progressive and selective activation of somatosensory and limbic system structures in the brain and brainstem following the subcutaneous injection of formalin.
Abstract: Pain is a unified experience composed of interacting discriminative, affective-motivational, and cognitive components, each of which is mediated and modulated through forebrain mechanisms acting at spinal, brainstem, and cerebral levels. The size of the human forebrain in relation to the spinal cord gives anatomical emphasis to forebrain control over nociceptive processing. Human forebrain pathology can cause pain without the activation of nociceptors. Functional imaging of the normal human brain with positron emission tomography (PET) shows synaptically induced increases in regional cerebral blood flow (rCBF) in several regions specifically during pain. We have examined the variables of gender, type of noxious stimulus, and the origin of nociceptive input as potential determinants of the pattern and intensity of rCBF responses. The structures most consistently activated across genders and during contact heat pain, cold pain, cutaneous laser pain or intramuscular pain were the contralateral insula and anterior cingulate cortex, the bilateral thalamus and premotor cortex, and the cerebellar vermis. These regions are commonly activated in PET studies of pain conducted by other investigators, and the intensity of the brain rCBF response correlates parametrically with perceived pain intensity. To complement the human studies, we developed an animal model for investigating stimulus-induced rCBF responses in the rat. In accord with behavioral measures and the results of human PET, there is a progressive and selective activation of somatosensory and limbic system structures in the brain and brainstem following the subcutaneous injection of formalin. The animal model and human PET studies should be mutually reinforcing and thus facilitate progress in understanding forebrain mechanisms of normal and pathological pain.
371 citations
Journal Article•
TL;DR: In this article, magnetic source imaging revealed that the topographic representation in the somatosensory cortex of upper extremity amputees was shifted an average of 1.5 cm toward the area that would normally receive input from the now absent nerves supplying the hand and fingers.
Abstract: MAGNETIC source imaging revealed that the topographic representation in the somatosensory cortex of the face area in upper extremity amputees was shifted an average of 1.5 cm toward the area that would normally receive input from the now absent nerves supplying the hand and fingers. Observed alterat
348 citations
TL;DR: The study indicates that oromandibular-facial trauma, including dental procedures, may precipitate the onset of OMD, especially in predisposed people, and prompt recognition and treatment may prevent further complications.
Abstract: OBJECTIVES—Oromandibular dystonia (OMD) is a focal dystonia manifested by involuntary muscle contractions producing repetitive, patterned mouth, jaw, and tongue movements. Dystonia is usually idiopathic (primary), but in some cases it follows peripheral injury. Peripherally induced cervical and limb dystonia is well recognised, and the aim of this study was to characterise peripherally induced OMD.
METHODS—The following inclusion criteria were used for peripherally induced OMD: (1) the onset of the dystonia was within a few days or months (up to 1 year) after the injury; (2) the trauma was well documented by the patient's history or a review of their medical and dental records; and (3) the onset of dystonia was anatomically related to the site of injury (facial and oral).
RESULTS—Twenty seven patients were identified in the database with OMD, temporally and anatomically related to prior injury or surgery. No additional precipitant other than trauma could be detected. None of the patients had any litigation pending. The mean age at onset was 50.11 (SD 14.15) (range 23-74) years and there was a 2:1 female preponderance. Mean latency between the initial trauma and the onset of OMD was 65 days (range 1 day-1 year). Ten (37%) patients had some evidence of predisposing factors such as family history of movement disorders, prior exposure to neuroleptic drugs, and associated dystonia affecting other regions or essential tremor. When compared with 21 patients with primary OMD, there was no difference for age at onset, female preponderance, and phenomenology. The frequency of dystonic writer's cramp, spasmodic dysphonia, bruxism, essential tremor, and family history of movement disorder, however, was lower in the post-traumatic group (p<0.05). In both groups the response to botulinum toxin treatment was superior to medical therapy (p<0.005). Surgical intervention for temporomandibular disorders was more frequent in the post-traumatic group and was associated with worsening of dystonia.
CONCLUSION—The study indicates that oromandibular-facial trauma, including dental procedures, may precipitate the onset of OMD, especially in predisposed people. Prompt recognition and treatment may prevent further complications.
157 citations
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224 citations
TL;DR: Sensory stimuli to the body are conveyed by the spinal cord to the primary somatosensory cortex, which is highly dependent on dorsal spinal column inputs, and other spinal pathways do not substitute for the dorsal columns even after 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.
195 citations
"REVIEW ■ : Reorganization of Sensor..." refers background in this paper
...were specifically designed to assess the possibility of cortical reorganization following dorsal column section (32, 33)....
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TL;DR: It is concluded that GAD-immunoreactivity in the barrel cortex swiftly reacts to modifications of neuronal activity evoked in the periphery, coincident with the regeneration of peripheral nerve fibres in the absence of their follicles.
Abstract: The whisker-to-barrel pathway of the adult mouse was used in a study on the effects of peripheral sensory deprivation on GAD-immunoreactivity in the somatosensory cortex. At varying periods of time after removal of a set of vibrissal follicles, mice were processed for immunohistochemistry using an antibody against GAD. In sections tangential to the cortical surface we observed, in the barrels whose follicles were removed, decreased immunoreactivity as early as three days after surgery. The decrease was due to a lesser numerical density of stained puncta and to less intense staining of those remaining. GAD-positive somata were also less intensely stained, whereas their number did not seem to be changed. The changes, apparent at 3 days after the surgery, were restricted to the barrels corresponding to the removed follicles and were maximal at 2–4 weeks. At longer survival times (until 7 months) the immunoreactivity returned to normal, coincident with the regeneration of peripheral nerve fibres in the absence of their follicles. We conclude that GAD-immunoreactivity in the barrel cortex swiftly reacts to modifications of neuronal activity evoked in the periphery.
166 citations
TL;DR: The primary somatosensory cortex of small rodents is an isomorphic representation of the body surface that develops in a sequence that begins at the periphery, and that ends in the cortex, and central representations at all levels of the neural axis are altered by perinatal perturbations of the peripheral surface.
164 citations
"REVIEW ■ : Reorganization of Sensor..." refers background in this paper
...At least crude outlines of these representations emerge early in development, and they are shaped thereafter by experience to produce finely tuned maps of the receptor arrays (1-3)....
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TL;DR: Electrophysiological recording in the ventroposterior lateral nucleus has revealed that not only can reorganization occur in the thalamus, but it may be as extensive as that revealed in the cortex of the same monkeys.
Abstract: Large changes in somatotopic organization can be induced in adult primate somatosensory cortex by cutting peripheral afferents. The role, if any, of the thalamus in these changes has not been investigated previously. In the present experiments, electrophysiological recording in the ventroposterior lateral nucleus (VPL) has revealed that not only can reorganization occur in the thalamus, but it may be as extensive as that revealed in the cortex of the same monkeys. Thus, for at least some types of deafferentation, the reorganization revealed in the cortex may depend largely on subcortical changes.
161 citations
"REVIEW ■ : Reorganization of Sensor..." refers background in this paper
...1 c), for example, occurs subcortically (51), probably at the level of the cuneate nucleus....
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