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At least 613 records · Page 34Linked to original sources

PubMed1996

The high-affinity sulphonylurea receptor regulates KATP channels in nerve terminals of the rat motor cortex.

The coexpression of sulphonylurea binding sites and ATP-sensitive K+(KATP) channels was examined in the rat motor cortex, an area of the CNS exhibiting a high density of sulphonylurea binding. These channels were not detected on neuronal cell bodies, but sulphonylurea-sensitive KATP channels and charybdotoxin-sensitive, large-conductance calcium-activated K+ BKCa channels were detected by patch clamping of fused nerve terminals from the motor cortex. Subcellular fractionation revealed that high-affinity sulphonylurea binding sites were enriched in the nerve terminal fraction, whereas glibenclamide increased calcium-independent glutamate efflux from isolated nerve terminals. It is concluded that neuronal sulphonylurea receptors and KATP channels are functionally linked in the motor cortex and that they are both selectively expressed in nerve terminals, where the KATP channel may serve to limit glutamate release under conditions of metabolic stress.

ATP-Binding Cassette Transporters↗

PubMed1992

Percutaneous magnetic stimulation of the motor cortex in migraine.

We have used transcranial magnetic stimulation of the motor cortex interictally in 12 patients with unilateral classic migraine with sensorimotor auras and 10 patients with common migraine and unilateral headache. In classic migraine, the threshold of activation of the FDI muscle by the cortical stimulus was significantly increased on the side of the auras, when compared to the unaffected side (P less than 0.01) and to normal subjects (P less than 0.01). The amplitude of EMG responses was also reduced in FDI on the affected side when compared to normals (P less than 0.02). Responses obtained in common migraine patients were normal on both sides. We suggest that some permanent subclinical dysfunction of the motor cortex might play a role in the pathogenesis of attacks of classic migraine with sensorimotor auras.

Adolescent↗

PubMed1994

A quantitative autoradiographic study of [3H]kainate binding sites in the normal human spinal cord, brainstem and motor cortex.

The quantitative autoradiographic distribution of the kainate subtype of non-NMDA receptor in the normal human motor cortex, brainstem and spinal cord has been investigated using [3H]kainate. In the motor cortex specific [3H]kainate binding was present in all cortical laminae with the highest density in laminae and II and the upper part of III and lower densities in the middle and deep laminae. In the premotor cortex a band of high density was found in laminae V and VI as well as in the superficial laminae. In the normal brainstem kainate receptors had a heterogeneous distribution. Brainstem motor nuclei which tend to be affected in motor neuron disease (MND) had very low densities of binding sites, whereas the oculomotor nucleus had a higher density. Specific [3H]kainate binding was found throughout the spinal grey matter, the greatest density being found in the substantia gelatinosa and much lower densities in the rest of the grey matter including the ventral horns. Excitotoxicity at non-NMDA receptors has been implicated in the pathogenesis of MND. This study shows that the motor neuron groups vulnerable in MND express a low density of [3H]kainate binding sites and suggests that the density of kainate receptors does not account for selective vulnerability in this disorder.

Adult↗

PubMed2005

Motor cortex dynamics in visuomotor production of speech and non-speech mouth movements.

We investigated timing and hemispheric balance of motor cortex activation when kinetically similar speech and non-speech mouth movements and sequences of such movements were triggered by visually presented letter- and symbol-strings. As an index of motor cortex activation, we used magnetoencephalographic recording of task-related change of precentral 20 Hz (16-24 Hz) activity. Suppression of the 20 Hz rhythm revealed pre-movement activation in the face representation areas that was tied to visual instruction, not movement onset. The 20 Hz rhythm remained suppressed throughout the preparation and execution of mouth movements and was followed by post-movement rebound. Left hemisphere preceded the right at the onset and offset of the suppression, similarly for isolated and sequential speech and non-speech movements. Pattern of task-related change in 20 Hz activity was otherwise symmetrical. In the face areas, the overall modulation of 20 Hz activity increased with sequence length and motor demands. Hand representation areas showed also weak reactivity, with systematically larger modulation of 20 Hz activity for non-speech than speech movements. Our results suggest an active role for the motor cortex in cognitive control of visually triggered mouth movements, not limited to movement execution.

Adult↗

PubMed1988

Relations of motor cortex neural discharge to kinematics of passive and active elbow movements in the monkey.

1. Bedingham and Tatton recently reported that in cats trained not to resist imposed limb perturbations, some motor cortex (area 4) neurons responded predominantly to acceleration or jerk (the third derivative of position). The questions arose whether motor cortex neurons responding to higher derivatives of limb displacement exist in the primate in a resist-perturbation task and, if so, whether discharge of such neurons responds to the same kinematics in active (voluntary) movements. 2. To answer these questions we studied the discharge patterns of 203 motor cortex neurons that responded to torque pulse perturbations about the elbow and fired during active elbow flexions and extensions in four monkeys. Detailed analysis was performed on 66 neurons that responded reciprocally in both situations. 3. Reciprocal neurons discharged at short latency (20-40 ms) for one direction of arm perturbation. For the opposite direction they were initially silent or inhibited and then discharged at a variety of latencies but in apparent relation to limb kinematics. Based on the timing and overall pattern of their discharge the majority of neurons (68%) were classified as being acceleration-like. 4. Twenty-four (36%) of these reciprocal neurons had only sensory (kinematic)-like properties in active movements, i.e., they discharged after (and not before) movement onset. Discharge of these neurons followed the timing, but not the magnitude, of acceleration (20 neurons) or velocity (4 neurons). The discharge of these neurons also had a static component as the arm was held stationary. 5. Twenty-nine (44%) of reciprocal neurons commenced firing before movement onset for one direction of active movement, while for the opposite direction their discharge occurred after movement onset. Thus their discharge appeared to be muscle-related: both when the muscle was contracting as an agonist and stretched as an antagonist. 6. Although in these tasks discharge of MCNs could be generated either by sensory feedback or by motor responses, the strong response sensitivity of many neurons to acceleration supports the hypothesis that feedback based on higher derivatives of limb displacement could represent a "predictive" control system for accurate regulation of limb motion.

Action Potentials↗

PubMed2006

Transhemispheric functional reorganization of the motor cortex induced by the peripheral contralateral nerve transfer to the injured arm.

Peripheral nerve injury in a limb usually causes functional reorganization of the contralateral motor cortex. However, a dynamic process of the novel transhemispheric functional reorganization in the motor cortex was found in adult rats after transferring the seventh cervical nerve root from the contralateral healthy side to the injured limb. Initially the ipsilateral motor cortex activated the injured forepaw for 5 months after the operation. Then, both hemispheres of the cortex activated the injured forepaw, and finally the contralateral cortex exclusively controlled the injured forepaw. It is concluded an extensive functional shift occurred between two hemispheres based on neural plasticity in the CNS. The experimental results of the later lesions of the ipsilateral cortex suggest that maintaining transhemispheric functional reorganization does not depend on the corpus callosum, but depends on mechanisms involving central axonal sprouting. Possible mechanisms underlying the alternative changes in cortical functions were discussed in rats and in patients having similar operations.

Animals↗

PubMed1990

IgG reactivity in the spinal cord and motor cortex in amyotrophic lateral sclerosis.

The spinal cord and motor cortex of patients with amyotrophic lateral sclerosis (ALS) were examined with immunohistochemical methods for the presence of IgG. In 13 of 15 spinal cords, a population of motoneurons stained positively for IgG in a granular pattern, characteristic of binding to the rough endoplasmic reticulum. In 6 of 11 motor cortices, a proportion of pyramidal cells also stained positively for IgG. No such reactivity was noted in motoneurons of control human tissues, although positive IgG staining was present in astrocytes of ALS and control specimens. Reactive microglia and/or macrophages were detected in the territory of degenerating pyramidal tracts and ventral horns. The surface of most of these cells stained positively for IgG, and 50% stained positively for HLA-DR. The accumulation of IgG in motoneurons and the presence of immunologically active macrophages provide additional evidence for the participation of immunologic factors in the pathogenesis of ALS.

Adult↗

PubMed1990

Primary motor cortex receives input from area 3a in macaques.

Intracortical microstimulation was used to define topographic sectors and the rostral border of primary motor cortex in adult macaques (Macaca mulatta). In the same animals, injections of fluorescent tracers were made within defined regions of primary motor cortex. Retrogradely labeled neurons were topographically distributed in area 3a, with most neurons located in layer III, and fewer neurons situated in layers V and IV. These findings suggest that muscle afferent information, thought to be important in a closed-loop mode of function, may reach primary motor cortex directly from cortical area 3a.

Animals↗

PubMed2004

Learning-induced improvement in encoding and decoding of specific movement directions by neurons in the primary motor cortex.

Many recent studies describe learning-related changes in sensory and motor areas, but few have directly probed for improvement in neuronal coding after learning. We used information theory to analyze single-cell activity from the primary motor cortex of monkeys, before and after learning a local rotational visuomotor task. We show that after learning, neurons in the primary motor cortex conveyed more information about the direction of movement and did so with relation to their directional sensitivity. Similar to recent findings in sensory systems, this specific improvement in encoding is correlated with an increase in the slope of the neurons' tuning curve. We further demonstrate that the improved information after learning enables a more accurate reconstruction of movement direction from neuronal populations. Our results suggest that similar mechanisms govern learning in sensory and motor areas and provide further evidence for a tight relationship between the locality of learning and the properties of neurons; namely, cells only show plasticity if their preferred direction is near the training one. The results also suggest that simple learning tasks can enhance the performance of brain-machine interfaces.

Animals↗

PubMed1995

Thalamocortical and corticocortical excitatory postsynaptic potentials mediated by excitatory amino acid receptors in the cat motor cortex in vivo.

Intracellular recordings were made from neurons in the motor cortex of an anaesthetized cat, together with iontophoretic application of excitatory amino acid receptor agonists and antagonists, in order to evaluate the role of such receptors in excitatory postsynaptic potentials evoked from stimulation of afferent and recurrent pathways in vivo. Excitatory postsynaptic potentials which were evoked by stimulation of the ventrolateral thalamus were found to be largely insensitive to antagonism by N-methyl-D-aspartate receptor antagonists, although they were susceptible to blockade by the non-N-methyl-D-aspartate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione. Increasing the ventrolateral thalamus stimulation frequency from 0.5 or 1 to 5 Hz caused an increase of evoked excitatory postsynaptic potential amplitudes and number of action potentials. These augmented excitatory postsynaptic potentials remained insensitive to application of N-methyl-D-aspartate antagonists. In contrast, recurrent excitatory postsynaptic potentials evoked by stimulation of the pyramidal tract were found to be sensitive to N-methyl-D-aspartate receptor antagonists and/or non-N-methyl-D-aspartate receptor antagonists in some neurons. These results demonstrate the involvement of both N-methyl-D-aspartate- and non-N-methyl-D-aspartate receptors in synaptic responses of cat motor cortex neurons in vivo, and that the synaptic pharmacology of the thalamic input may differ from that of the local recurrent pathways.

2-Amino-5-phosphonovalerate↗

PubMed1989

Changes in synaptic density in motor cortex of rhesus monkey during fetal and postnatal life.

The density and proportion of synaptic contacts in the primate motor cortex (Brodmann area 4) were determined in 21 rhesus monkeys ranging in age from embryonic day 41 (E41) to 20 years. Two to 4 vertical electron microscopic probes, each consisting of 150-250 overlapping micrographs traversing the thickness of the cortex, were prepared for each specimen. Synapses were categorized according to their morphology (symmetrical or asymmetrical), cellular location (on spines, shafts or soma), number, and ratio of laminar distribution. The density of synapses was expressed per unit area and volume of neuropil (excluding neuronal and glia cell bodies, myelin sheath, blood vessels and extracellular space). The first synapse in the area of the emerging motor cortex were observed at E53 in the marginal zone (prospective layer I) and in the transient subplate zone situated beneath the developing cortical plate. Around midgestation (E89) synapses were observed over the entire width of the cortical plate, and their density was about 5/100 microns 3 of neuropil. During the last two months of gestation synaptic density increased 8-fold across all layers to reach about 40/100 microns 3 at the time of birth (E165). Synaptic production continued postnatally and by the end of the second postnatal month attained a level of 60/100 microns 3 neuropil which is two times higher than in the adults. This level decreased at a slow rate until sexual maturity (3 years of age) and then more rapidly to the adult level which is characterized by relative stability of about 30/100 microns 3. The decline in synaptic density after the peak in infancy occurs predominantly at the expense of asymmetric synapses situated on dendritic spines; the population of symmetric synapses on dendritic shafts remains relatively constant. The development of synaptic connections in the motor cortex of non-human primates involves initial overproduction followed by selective elimination and structural alterations.

Aging↗

PubMed2001

Finger somatotopy in human motor cortex.

Although qualitative reports about somatotopic representation of fingers in the human motor cortex exist, up to now no study could provide clear statistical evidence. The goal of the present study was to reinvestigate finger motor somatotopy by means of a thorough investigation of standardized movements of the index and little finger of the right hand. Using high resolution fMRI at 3 Tesla, blood oxygenation level-dependent (BOLD) responses in a group of 26 subjects were repeatedly measured to achieve reliable statistical results. The center of mass of all activated voxels within the primary motor cortex was calculated for each finger and each run. Results of all runs were averaged to yield an individual index and little finger representation for each subject. The mean center of mass localizations for all subjects were then submitted to a paired t test. Results show a highly significant though small scale somatotopy of fingerspecific activation patterns in the order indicated by Penfields motor homunculus. In addition, considerable overlap of finger specific BOLD responses was found. Comparing various methods of analysis, the mean center of mass distance for the two fingers was 2--3 mm with overlapping voxels included and 4--5 mm with overlapping voxels excluded. Our data may be best understood in the context of the work of Schieber (1999) who recently described overlapping somatotopic gradients in lesion studies with humans.

Adult↗

PubMed1994

Identification of the cerebral motor cortex by focal magnetic stimulation: clinical application to neurosurgical patients.

A figure-8 coil was designed that was capable of generating currents over a relatively limited area. In this study, we used the figure-8 coil to localize human cerebral motor cortex by transcranial magnetic stimulation and assessed its value as a diagnostic tool for neurosurgical disease. The subjects were 10 normal volunteers and 12 neurosurgical patients. The points obtaining a response were plotted and the response area was delineated for each stimulus output. Rectangular coordinates were subsequently determined for the C3-Cz-C4 line with the stimulation sites set 1.0 cm apart. Then amplitude and latency maps were displayed by a computer wave map program. In normal volunteers, the posterior margin of the site where a threshold +5% stimulus obtained a response from the THE or ADM muscles almost coincided with the central sulcus. The optimal areas were relatively narrow on the amplitude and latency maps. In the patient with a left frontal convexity meningioma, the left threshold +5% area for the THE and ADM muscles showed marked anterolateral shift. No threshold map could be obtained on the affected side in patients with metastatic tumor and astrocytoma. Low perfusion areas caused by moyamoya disease and arteriovenous malformations produced narrowing of the optimal zone on the threshold map of the affected side. Hyperexcitability of the motor cortex was recognized in the arteriovenous malformation patients. Transcranial focal magnetic stimulation is a useful noninvasive diagnostic method for identification of the human cerebral motor cortex. It provides important information about changes in the localization and excitability of the motor cortex in neurosurgical patients and should be helpful for treatment planning.

Adult↗

PubMed1997

Assessment of corticospinal function in spinal cord injury using transcranial motor cortex stimulation: a review.

Other than clinical examination, few methods exist for assessing the functional condition of descending long tracts of the spinal cord in humans. This review covers neurophysiological examination of the corticospinal system using transcranial electrical and magnetic motor cortex stimulation. The neurophysiological basis for the motor evoked potentials (MEPs) and the differences between the two methods are discussed followed by a review of their use in individuals with spinal cord injury (SCI). Transcranial motor cortex stimulation is used to monitor descending spinal cord tract condition during spinal surgeries and could be useful for assessing central nervous system trauma, especially in the unconscious multitrauma patient. In the chronic phase of SCI, recordings of MEPs have enabled the estimation of central conduction times that relate to the condition of axons passing through the injured segment of the spinal cord. They were found to correlate well with clinical examination scores but as predictors of outcome, the reports have been mixed. The use of transcranial motor cortex stimulation to modify segmental reflexes and in combination with volitional attempts have also provided evidence of conduction across the lesion in paralyzed SCI subjects. However, MEPs can be absent in some SCI individuals who may be able to volitionally activate muscles below the level of the spinal cord lesion. Such findings are useful in elucidating the neural mechanisms underlying the performance of a volitional movement and may serve to guide and monitor the effects of future treatments for paralysis in SCI and other neurological disorders.

Animals↗

PubMed1998

Dextromethorphan decreases the excitability of the human motor cortex.

OBJECTIVE: To assess the acute effects of dextromethorphan (DM) on human motor cortical excitability. BACKGROUND: DM, a noncompetitive N-methyl-D-aspartate receptor antagonist, has recently attracted clinical interest for its potential as a neuroprotective agent in various models of excitotoxicity. We were interested in learning whether this drug can modulate the excitability of the motor cortex in healthy subjects. METHODS: The effects of DM on the excitability of the normal human motor cortex were studied in eight healthy volunteers by means of focal transcranial magnetic stimulation before and 1.5, 4, 6.5, and 24 hours after a single oral dose of 150 mg DM. Motor evoked potentials (MEPs) were recorded from the relaxed abductor digiti minimi muscle. Measures of motor cortical excitability were motor threshold, MEP recruitment, duration of the cortical silent period, and intracortical inhibition and facilitation. In addition, the authors explored spinal and neuromuscular excitability by means of F waves, duration of the peripheral silent period, and maximum M wave. RESULTS: Intracortical inhibition increased temporarily, intracortical facilitation decreased, and the cortical silent period lengthened slightly. Motor threshold, MEP recruitment, and spinal and peripheral motor excitability were not affected significantly. CONCLUSIONS: Our findings suggest that DM can exert a significant suppression of the excitatory drive in the normal human cortex, which may be relevant for its potential therapeutic use in excitotoxicity-related neurologic disease. Furthermore, the noninvasive technique described may prove useful in preclinical studies to assess the effects on motor cortical excitability induced by new modulators of glutamatergic transmission currently under development.

Adult↗

PubMed1997

Rapid astroglial reactions in the motor cortex of adult rats following peripheral facial nerve lesions.

We report on changes in the motor cortex of adult rats that rapidly and transiently followed various types of facial nerve lesions. These reactions led to enhanced immunoreactivities of various astroglial markers: S-100 protein (a Ca2+- and Zn2+-binding protein predominantly located in the cytosol of astrocytes), glial fibrillary acidic protein (a cytoskeletal protein) and connexin 43 (the astroglial gap junction protein). Reactions could be visualized 1 h after the facial nerve lesion and disappeared within about 5 days after surgery. Combined lesions of the facial and trigeminal nerves modified the spatial pattern of the astroglial reaction, similar to intramuscular injections of botulinum toxin, which inhibits the release of acetylcholine in motor endplates. Data presented suggest that peripheral interference with muscular functions rapidly induces modifications in the motor cortex.

Acetylcholine↗

PubMed2002

Laminar-dependent dendritic spine alterations in the motor cortex of adult rats following callosal transection and forced forelimb use.

Previously, the authors found that partial denervation of the motor cortex in adult animals can enhance this region's neuronal growth response to relevant behavioral change. Rats with partial corpus callosum transections that were forced to rely on one forelimb for 18 days had increased dendritic arborization of layer V pyramidal neurons in the opposite motor cortex compared to controls. This was not found as a result of denervation alone or of forced forelimb use alone. However, it seemed possible that each independent manipulation (i.e., forced forelimb use alone and callosal transections alone) resulted in neural structural alterations that were simply not revealed in measurements of dendritic branch number and/or not inclusive of layer V dendrites. This possibility was assessed in the current study with a reexamination of the Golgi-Cox impregnated tissue generated in the previous study. Tissue was quantified from rats that received either partial transections of the rostral two-thirds of the corpus callosum (CCX) or sham operations (Sham) followed either by 18 days of forced use of one forelimb (Use) or unrestricted use of both forelimbs (Cont). Measurements of apical and basilar dendrites from pyramidal neurons of layer II/III and layer V were performed to detect spine addition resulting from either increased spine density or the addition of dendritic material. As hypothesized, significant spine addition was found following forced forelimb use alone (Sham+Use) and callosal transections alone (CCX+Cont). However, forced use primarily increased spines on layer II/III pyramidal neurons, whereas callosal transections primarily increased dendritic spines on layer V pyramidal neurons in comparison to Sham+Cont. A much more robust increase in layer V dendritic spines was found in animals with the combination of forced forelimb use and denervation (CCX+Use). In contrast to the effects of forced use alone, however, CCX+Use rats failed to show major net increases in spines on layer II/III neurons. These results indicate that while callosal denervation may greatly enhance the neuronal growth and synaptogenic response to behavioral change in layer V, it may also limit spine addition associated with forced forelimb use in layer II/III of the motor cortex.

Animals↗

PubMed2000

Motor cortex fatigue in sports measured by transcranial magnetic double stimulation.

PURPOSE: Besides peripheral mechanisms, central fatigue is an important factor limiting the performance of exhausting exercise in sport. The mechanisms responsible are still in discussion. Using noninvasive transcranial magnetic stimulation (TMS) in a double-pulse technique, we sought to assess fatigue of the motor cortex after exhaustive anaerobic strain. METHODS: 23 male subjects (22-52 yr) taking part in the study were requested to accomplish as many pull-ups as possible until exhaustion. The amount of physical lifting work was recorded. Before and immediately after the task, intracortical inhibition (ICI) and facilitation (ICF) were measured by a conditioned-test double-pulse TMS method for the right brachioradialis (BR) and abductor pollicis brevis muscle (APB). RESULTS: After exercise, ICF was significantly reduced in the BR but not in the APB. ICI was not altered. Changes tended to normalize within 8 min after the task. The amount of lifting work accomplished showed significant correlation to the values of ICF reduction (r = 0.73). Moreover, the baseline values of ICF before exercise were also significantly correlated to the lifting work (r = 0.63). CONCLUSIONS: Because double-pulse TMS gives access to the motor cortex independently of spinal or peripheral mechanisms, reduced ICF reflects decreased excitability of interneuronal circuits within the motor cortex. We suggest that ICF measures motor cortex fatigue after exhausting strain specifically for the muscles performing the task. Gamma-aminobutyric acid (GABA)-ergic neurotransmission is possibly involved in the mechanisms mediating central fatigue. Double-pulse TMS may be a useful tool in the control of training in sports as well as in the detection of pathological central fatigue in overreaching and in the prevention of overtraining.

Adult↗