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Cortical Representation (cortical + representation)
Selected AbstractsRapid functional plasticity in the primary somatomotor cortex and perceptual changes after nerve blockEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2004Thomas Weiss Abstract The mature human primary somatosensory cortex displays a striking plastic capacity to reorganize itself in response to changes in sensory input. Following the elimination of afferent return, produced by either amputation, deafferentation by dorsal rhizotomy, or nerve block, there is a well-known but little-understood ,invasion' of the deafferented region of the brain by the cortical representation zones of still-intact portions of the brain adjacent to it. We report here that within an hour of abolishing sensation from the radial and medial three-quarters of the hand by pharmacological blockade of the radial and median nerves, magnetic source imaging showed that the cortical representation of the little finger and the skin beneath the lower lip, whose intact cortical representation zones are adjacent to the deafferented region, had moved closer together, presumably because of their expansion across the deafferented area. A paired-pulse transcranial magnetic stimulation procedure revealed a motor cortex disinhibition for two muscles supplied by the unaffected ulnar nerve. In addition, two notable perceptual changes were observed: increased two-point discrimination ability near the lip and mislocalization of touch of the intact ulnar portion of the fourth finger to the neighbouring third finger whose nerve supply was blocked. We suggest that disinhibition within the somatosensory system as a functional correlate for the known enlargement of cortical representation zones might account for not only the ,invasion' phenomenon, but also for the observed behavioural correlates of the nerve block. [source] Reduced plasticity of cortical whisker representation in adult tenascin-C-deficient mice after vibrissectomyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Anita Cybulska-Klosowicz Abstract The effect of the extracellular matrix recognition molecule tenascin-C on cerebral plasticity induced by vibrissectomy was investigated with 2-deoxyglucose (2DG) brain mapping in tenascin-C-deficient mice. Unilateral vibrissectomy sparing row C of vibrissae was performed in young adult mice. Two months later, cortical representations of spared row C vibrissae and control row C on the other side of the snout were visualized by [14C]2DG autoradiography. In both wild-type and tenascin-C-deficient mice, cortical representation of the spared row was expanded in all layers of the barrel cortex. However, the effect was significantly more extensive in wild-type animals than in the mutant. Elimination of tenascin-C by genetic manipulation thus reduces the effect of vibrissectomy observed in the somatosensory cortex. No increase in number of fibres in the vibrissal nerve of spared vibrissae was seen, and occurrence of additional nerve to the spared follicle was very rare. Thus, in tenascin-C-deficient mice functional plasticity seems to be impaired within the CNS. [source] Mechanisms underlying human motor system plasticity,MUSCLE AND NERVE, Issue 5 2001Babak Boroojerdi MD Abstract There has been increased interest in the ability of the adult human nervous system to reorganize and adapt to environmental changes throughout life. This ability has been termed "plasticity." Plastic changes in the cerebral cortex have been studied: (a) as modifications of sensory or motor cortical representation of specific body parts (cortical maps, body representation level); and (b) as changes in the efficacy of existing synapses or generation of new synapses (neuronal or synaptic level). In this review, we describe paradigms used to study mechanisms of plasticity in the intact human motor system, the functional relevance of such plasticity, and possible ways to modulate it. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 602,613, 2001 [source] Representation of the standard: Stimulus context effects on the process generating the mismatch negativity component of event-related brain potentialsPSYCHOPHYSIOLOGY, Issue 3 2003Elyse Sussman Abstract In the auditory oddball paradigm, the frequent occurrence of a sound (the "standard") forms the basis of deviance detection. The incoming sounds are compared with the cortical representation of the standard and those sounds that do not match it elicit the mismatch negativity (MMN) event-related brain potential. Here we address the issue of whether the relative probability of the sounds in a sequence was a critical factor influencing which sounds would be represented as standards in the deviant comparison process. One frequent (F1) and two infrequent (D1 and D2) sounds that differed only in duration were presented in a sequence. D1 occurred proportionally as frequently with respect to D2 as F1 occurred with respect to D1. If the proportional relationship of sounds were critical then D1 could serve as a "standard" to D2 and thus D2 should elicit two MMNs. However, D2 elicited MMN only with respect to F1. This result as well as those obtained in two control conditions suggests that "standards" are not established on the basis of relative probability; they emerge as a result of global characteristics, the longer-term context, of the sound sequence. [source] Intracortical modulation of cortical-bulbar responses for the masseter muscleTHE JOURNAL OF PHYSIOLOGY, Issue 14 2008Enzo Ortu Short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were evaluated in the masseter muscles of 12 subjects and the cortical silent period (SP) in nine subjects. Motor evoked potentials (MEPs) were recorded from contralateral (cMM) and ipsilateral (iMM) masseters, activated at 10% of maximal voluntary contraction (MVC). Interstimulus intervals (ISIs) were 2 and 3 ms for SICI, 10 and 15 ms for ICF. TMS of the left masseteric cortex induced MEPs that were larger in the cMM than the iMM; stimulation of right masseteric cortex produced a similar asymmetry in response amplitude. SICI was only observed using a CS intensity of 70% AMT and was equal in both cMM and iMM. SICI was stronger at higher TS intensities, was abolished by muscle activation greater than 10% MVC, and was unaffected by coil orientation changes. Control experiments confirmed that SICI was not contaminated by any inhibitory peripheral reflexes. However, ICF could not be obtained because it was masked by bilateral reflex depression of masseter EMG caused by auditory input from the coil discharge. The SP was bilateral and symmetric; its duration ranged from 35 to 70 ms depending on TS intensity and coil orientation. We conclude that SICI is present in the cortical representation of masseter muscles. The similarity of SICI in cMM and iMM suggests either that a single pool of inhibitory interneurons controls ipsi- and contralateral corticotrigeminal projections or that inhibition is directed to bilaterally projecting corticotrigeminal fibres. Finally, the corticotrigeminal projection seems to be weakly influenced by inhibitory interneurons mediating the cortical SP. [source] Frequency Map Variations in Squirrel Monkey Primary Auditory Cortex,THE LARYNGOSCOPE, Issue 7 2005Steven W. Cheung MD Abstract Objective: The goal of this work is to understand the neural basis for cortical representation of hearing in highly vocal primates to gain insights into the substrates for communication. Variation patterns in frequency representation among animals are incorporated into an explanatory model to reconcile heterogeneous observations. Study Design: Prospective. Methods: Thirty-four squirrel monkeys underwent microelectrode mapping experiments in primary auditory cortex (AI) using tone pip stimuli. Characteristic frequency (CF) was extracted from the excitatory frequency receptive field. Frequency maps were reconstructed using Voronoi-Dirichlet tessellation. The spatial locations (rostral vs. caudal) of highest CF isofrequency contours (minimum length 1 mm) and highest CF neuronal clusters on the temporal gyral surface were analyzed. Results: Isofrequency contours at least 1 mm long with CFs greater than 2.9 kHz (75% cases) are accessible on the temporal gyrus. Variability of the highest CF isofrequency contours accessible on the temporal gyrus has an interquartile range from 2.9 to 5.1 (mean 4.3) kHz. The highest CF isofrequency contours are located mainly in rostral AI, whereas the highest CF neuronal clusters flanking fully expressed isofrequency contours are equally distributed in rostral and caudal locations. Conclusions: Squirrel monkey AI frequency map variations are sizeable across animals and small within single animals (interhemispheric comparison). AI frequency map variations, modeled as translations and rotations relative to the lateral sulcus, are independent transfers. Caution must be exercised when interpreting nominal frequency map changes that are attributed to hearing loss and auditory learning effects. [source] Task-dependent modulation of functional connectivity between hand motor cortices and neuronal networks underlying language and music: a transcranial magnetic stimulation study in humansEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2007R. Sparing Abstract Although language functions are, in general, attributed to the left hemisphere, it is still a matter of debate to what extent the cognitive functions underlying the processing of music are lateralized in the human brain. To investigate hemispheric specialization we evaluated the effect of different overt musical and linguistic tasks on the excitability of both left and right hand motor cortices using transcranial magnetic stimulation (TMS). Task-dependent changes of the size of the TMS-elicited motor evoked potentials were recorded in 12 right-handed, musically naive subjects during and after overt speech, singing and humming, i.e. the production of melody without word articulation. The articulation of meaningless syllables served as control condition. We found reciprocal lateralized effects of overt speech and musical tasks on motor cortex excitability. During overt speech, the corticospinal projection of the left (i.e. dominant) hemisphere to the right hand was facilitated. In contrast, excitability of the right motor cortex increased during both overt singing and humming, whereas no effect was observed on the left hemisphere. Although the traditional concept of hemispheric lateralization of music has been challenged by recent neuroimaging studies, our findings demonstrate that right-hemisphere preponderance of music is nevertheless present. We discuss our results in terms of the recent concepts on evolution of language and gesture, which hypothesize that cerebral networks mediating hand movement and those subserving language processing are functionally linked. TMS may constitute a useful tool to further investigate the relationship between cortical representations of motor functions, music and language using comparative approaches. [source] Reduced plasticity of cortical whisker representation in adult tenascin-C-deficient mice after vibrissectomyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Anita Cybulska-Klosowicz Abstract The effect of the extracellular matrix recognition molecule tenascin-C on cerebral plasticity induced by vibrissectomy was investigated with 2-deoxyglucose (2DG) brain mapping in tenascin-C-deficient mice. Unilateral vibrissectomy sparing row C of vibrissae was performed in young adult mice. Two months later, cortical representations of spared row C vibrissae and control row C on the other side of the snout were visualized by [14C]2DG autoradiography. In both wild-type and tenascin-C-deficient mice, cortical representation of the spared row was expanded in all layers of the barrel cortex. However, the effect was significantly more extensive in wild-type animals than in the mutant. Elimination of tenascin-C by genetic manipulation thus reduces the effect of vibrissectomy observed in the somatosensory cortex. No increase in number of fibres in the vibrissal nerve of spared vibrissae was seen, and occurrence of additional nerve to the spared follicle was very rare. Thus, in tenascin-C-deficient mice functional plasticity seems to be impaired within the CNS. [source] Digit-specific aberrations in the primary somatosensory cortex in Writer's cramp,ANNALS OF NEUROLOGY, Issue 2 2009Aimee J. Nelson PhD Objective One approach to the treatment of focal hand dystonia (FHD) is via sensory-based training regimes. It is known that FHD patients demonstrate a reduced distance between the representations of digits 1 and 5 and also digits 2 and 5 in primary somatosensory cortex. However, we lack information on the spatial relationships among digits, such as reduced inter-digit spacing or shifts of representations within the cortical areas, and whether aberrations are specific to symptomatic digits. Our aim was to characterize the spatial relationships among individual digits to determine the types of aberrations that exist and whether these are specific to symptomatic digits only. Methods Using high-resolution fMRI over a limited volume and surface-based mapping techniques, the cortical representations of all digits of the dystonia-affected hand within the sub-regions of the postcentral gyrus were mapped in patients with task-specific Writer's cramp (WC). Results In area 3b, digits directly involved in writing (D1, D2 and D3) show reduced inter-digit separation, reversals, and overlapping activation. The thumb representation occupies territory normally occupied by digit 2 in controls. Asymptomatic digits 4 and 5 preserve their inter-digit separation yet shift towards the D1/D2/D3 cluster, suggesting that reduced spacing, not simply digit shifts, are associated with dystonia symptoms. Area 3a was less responsive to sensory input in WC patients providing evidence of reduced afferent drive or top-down modulation to this sub-region. Interpretation Therapeutic regimes aimed at facilitating inter-digit separation of digits 1, 2 and 3 may promote beneficial plasticity in WC patients. Ann Neurol 2009;66:146,154. [source] | |||||||||||||