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Results for “Motor Cortex”

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At least 883 records · Page 49Linked to original sources

PubMed2003

A computer model of neural processes observed in the cat motor cortex during performance of an operant movement.

This report describes a computer model of a "column" in the cat motor cortex. The model includes two layers of two-segment pyramidal neurons with two groups of inhibitory interneurons in each layer, which selectively control the somatic and dendritic segments of the pyramidal cells. In this model, neurons include active sodium, calcium, and several types of potassium currents. Excitatory connections between neurons are of the AMPA and NMDA types, while collateral connections between neurons of the upper layer are mainly of the NMDA type; connections between neurons in the lower layer are of the AMPA type. All inhibitory connections are of the GABA(A) type. The model reproduces the main neuronal processes seen in the cat motor cortex during performance of an operant movement. Pyramidal neurons of the upper layer generate primary and secondary responses to external stimuli. As in real experiments, secondary NMDA-dependent responses appear when GABA(A) inhibition is weakened and disappear when stimulation is increased; these properties of secondary responses are only reproduced when NMDA receptors are located in the terminals of collateral connections. Using only rapid NMDA-independent connections, neurons in the lower layer generate a slow bell-shaped wave of excitation (a "motor command"), which is formed by sequential activation of neurons with dendritic trees of different sizes.

Algorithms↗

PubMed2003

Early mitochondrial dysfunction occurs in motor cortex and spinal cord at the onset of disease in the Wobbler mouse.

The Wobbler mouse is recognized as an animal model for motoneuron disease that exhibits motoneuron pathology. We have recently demonstrated the occurrence of mitochondrial dysfunction in the Wobbler mouse brain. The aim of the present study was to evaluate whether mitochondrial dysfunction occurred at an early age at the time where disease symptoms appear, and whether it was more pronounced in the motor cortex or in the spinal cord. We report here a significant decrease in mitochondrial state 3 and 4 respiration rates at an early age in the Wobbler spinal cord. In addition, there was a pronounced decrease in oxidative phosphorylation in mitochondria isolated from both spinal cord and motor cortex in both age groups. This mitochondrial dysfunction was accompanied by impairment of complex I activity in mitochondria isolated from spinal cord at an early age. Decreases in complex III and IV activities were observed only in mitochondria isolated from the motor cortex at an early age, but impairment of complex III activity prevailed until later in the disease. We conclude that mitochondrial dysfunction ensues at an early stage of the disease and is more pronounced in the spinal cord, which correlates with previous studies that reported degeneration of spinal cord motorneurons.

Age Factors↗

PubMed2003

Differential impairment of individuated finger movements in humans after damage to the motor cortex or the corticospinal tract.

The purpose of this study was to quantify the long-term loss of independent finger movements in humans with lesions relatively restricted to motor cortex or corticospinal tract. We questioned whether damage to the motor cortex or corticospinal tract would permanently affect the ability to move each finger to the same degree or would affect some fingers more than others. People with pure motor hemiparesis due to ischemic cerebrovascular accident were used as our experimental sample. Pure motor hemiparetic and control subjects were tested for their ability to make cyclic flexion/extension movements of each finger independently. We recorded their finger joint motion using an instrumented glove. The fingers of control subjects and of the unaffected hands (ipsilateral to the lesion) of hemiparetic subjects moved relatively independently. The fingers of the affected hands (contralateral to the lesion) of hemiparetic subjects were differentially impaired in their ability to make independent finger movements. The independence of the thumb was normal; the independence of the index finger was slightly impaired, while the independence of the middle, ring, and little fingers was substantially impaired. The differential long-term effects of motor cortical or corticospinal damage on finger independence may result from rehabilitative training emphasizing tasks requiring independent thumb and index movements, and from a greater ability of the spared components of the neuromuscular system to control the thumb independently compared with the other four fingers.

Adult↗

PubMed2003

Transcranial magnetic stimulation reveals asymmetrical efficacy of intracortical circuits in primary motor cortex.

The efficacy of inhibitory and excitatory intracortical circuits acting on the representation of an intrinsic hand muscle in the primary motor cortex of both hemispheres was measured with paired transcranial magnetic stimuli in right-handed subjects. Both intracortical inhibition (measured with an interstimulus interval of 3 ms) and intracortical facilitation (measured with an interstimulus interval of 16 ms) developed more rapidly with increasing conditioning stimulus intensity in the dominant than the non-dominant hand. We conclude that the intracortical circuits in the primary motor cortex are more potent in the dominant than the non-dominant hemisphere, and hypothesize that this difference is a factor in the asymmetrical dexterity associated with hand preference.

Adolescent↗

PubMed2001

Neuronal clusters in the primate motor cortex during interception of moving targets.

Two rhesus monkeys were trained to intercept a moving target at a fixed location with a feedback cursor controlled by a 2-D manipulandum. The direction from which the target appeared, the time from the target onset to its arrival at the interception point, and the target acceleration were randomized for each trial, thus requiring the animal to adjust its movement according to the visual input on a trial-by-trial basis. The two animals adopted different strategies, similar to those identified previously in human subjects. Single-cell activity was recorded from the arm area of the primary motor cortex in these two animals, and the neurons were classified based on the temporal patterns in their activity, using a nonhierarchical cluster analysis. Results of this analysis revealed differences in the complexity and diversity of motor cortical activity between the two animals that paralleled those of behavioral strategies. Most clusters displayed activity closely related to the kinematics of hand movements. In addition, some clusters displayed patterns of activation that conveyed additional information necessary for successful performance of the task, such as the initial target velocity and the interval between successive submovements, suggesting that such information is represented in selective subpopulations of neurons in the primary motor cortex. These results also suggest that conversion of information about target motion into movement-related signals takes place in a broad network of cortical areas including the primary motor cortex.

Animals↗

PubMed1997

Tongue motor responses following transcranial magnetic stimulation of the motor cortex and proximal hypoglossal nerve in man.

Surface recordings of EMG responses were performed bilaterally from the tongue following transcranial magnetic cortex (TCS) and nerve stimulation (TNS) to characterize the activated corticonuclear pathways and to obtain normative data for a diagnostic use. TCS over the face-associated motor cortex with 1.3 times the response threshold for relaxed muscles produced bilateral tongue responses with similar latencies and amplitudes for ipsi-(8.3 +/- 1.1 ms, 1.3 +/- 0.7 mV) and contralateral responses (8.5 +/- 1.0 ms, 1.7 +/- 0.8 mV, n = 20, 10 subjects). In individual subjects maximal ipsilateral and contralateral responses were elicited by stimulation over about the same cortex area which lay 2-4 cm lateral and 0-2 cm anterior to the center of the hand motor representation area. Magnetic stimulation of the hypoglossal nerve with 70% of the maximal stimulator output and a circular coil placed over the posterior lateral skull produced a more proximal nerve excitation than electrical stimulation at the mandible, as reflected by the response latencies (3.4 +/- 0.9 ms vs. 2.1 +/- 0.7 ms). The effect of magnetic TNS was independent of the direction of the coil currents. Central motor latencies as calculated by subtracting the response latencies after TNS from the overall latency after TCS were 4.8 +/- 1.2 ms and 5.0 +/- 1.1 ms for ipsi- and contralateral responses, respectively. The findings suggest the existence of a direct and fast conducting connection between motor cortex and brainstem tongue motor nuclei on both sides in man.

Adult↗

PubMed2000

Reactive astrocytic responses to denervation in the motor cortex of adult rats are sensitive to manipulations of behavioral experience.

Recent research has suggested that mild denervation of the neocortex of adult rats may facilitate neuronal growth in response to behavioral changes. Astrocytes react to denervation, produce growth-promoting factors and are a potential mediator of this denervation-facilitated growth. The present study assessed whether astrocytic reactions to denervation vary dependent upon post-injury behavioral experience. Denervation of the transcallosal afferents to the motor cortex was induced via partial transections of the corpus callosum. Transected- or sham-operated rats were then either forced to use the opposite forelimb (via limb-restricting vests) or permitted to use both forelimbs normally for 8 days. In the motor cortex, the surface density of glial fibrillary acidic protein (GFAP)-immunoreactive (IR) astrocytic processes and the density of basic fibroblast growth factor (FGF-2)-IR glial cells was significantly increased as a result of transections alone and as a result of forced forelimb-use alone in comparison to controls. The combination of transections and forced-use significantly enhanced GFAP-IR in comparison to all other groups, but did not further enhance FGF-2-IR. These findings are consistent with behavior and denervation having interactive influences on astrocytic reactivity in the motor cortex. These results also raise the possibility that astrocyte-mediated support of neural restructuring after brain injury might be enhanced with appropriate post-injury behavioral manipulations.

Animals↗

PubMed2004

[Significance and usefulness of corticospinal motor evoked potential monitoring for lesions adjacent to primary motor cortex].

This study evaluated the usefulness of intraoperative corticospinal motor evoked potential (MEP) monitoring in preventing postoperative motor deficits, and whether this procedure contributed to surgery on intrinsic brain lesions in the vicinity of the motor area. The subjects were 45 patients with brain tumors located in and around the primary motor area. MEP was recorded through the cervical epidural electrodes in response to stimulation of the motor cortex. The amplitude of D-response of MEP was compared at the beginning and at the end of surgery. Then MEP changes were divided into five groups; "increase", "no change", "diminish", "decrease" and "disappear". We used the DeJong classification for qualitative analysis of motor function, and reviewed these findings in relation to the change in MEP. It was possible to record MEP when the preoperative motor weakness was DeJong 3 or better. There was no postoperative motor deficit when the MEP amplitude was preserved at better than 50% of a control amplitude. If the amplitude decreased to less than 50%, motor deficits were encoutered. When MEP amplitude increased during the surgery, preoperative motor weakness was improved after the surgery. It is concluded that there is little possibility of causing motor deficits even if tumor removal is aggressively pursued, as long as the amplitude of D-response remains at 50% or more of the baseline. This monitoring procedure is expected to improve the overall surgical results in patients with intrinsic brain tumors around the motor area.

Adolescent↗

PubMedDate not supplied

[Disruption of acquired head and paw movement coordination after unilateral lesioning of the motor cortex in dogs (a kinematic analysis)].

Dogs were trained to remove a cup with meat to the head bent down to the feeder and hold the limb flexed during eating. At the early stage of learning, the stable innate head-forelimb coordination characteristic for untrained animals was manifest. The forelimb flexion was accompanied by anticipatory lifting of the bent head, and the following bending of the head led to an extension of the flexed forelimb. The opposite coordination, i.e., the lifting and holding of the forelimb when the head is bent down, was achieved only by training. The lesion of the motor cortex contralateral to the working forelimb in the trained dogs led to a prolonged disturbance of the simultaneous holding of the flexed forelimb and the head bent down. The lesion of the motor cortex did not affect the individual movements but disturbed their coordination. In the operated dogs the innate relationships between the head and forelimb movement recovered. The results support the previous finding that the lesion of the motor cortex led to recovery of the innate coordination transformed in the process of learning.

Animals↗

PubMed2000

An fMRI study of the lateralization of motor cortex activation in acallosal patients.

Transcranial magnetic stimulation (TMS) studies have suggested that callosal afferents may mediate inhibition of the ipsilateral motor cortex (IMC) during unilateral hand movements. To test this concept, we used fMRI to determine whether acallosal patients have increased IMC activation with either complex or simple unilateral finger movements. Neither the localization of motor cortical regions activated, the volumes of activation, or the relative hemispheric lateralization of activations were different between the patients and normal controls. The potential callosal inhibitory pathway identified by TMS therefore does not appear to contribute to the interhemispheric suppression of physiologically relevant activations in the motor cortex as measured by fMRI.

Adult↗

PubMed2001

Orally administered atropine enhances motor cortex excitability: a transcranial magnetic stimulation study in human subjects.

Oral application of atropine was used to test if a modulation of cholinergic neurotransmission changed motor excitability. Healthy volunteers received either 1 or 2 mg atropine. Paired transcranial magnetic stimulation was used to study intracortical inhibition and intracortical facilitation before, 1 h and 24 h after ingestion of atropine. In addition, the silent period, motor threshold, F wave and motor response amplitudes were measured. The 1 mg dose of atropine induced a loss of intracortical inhibition, the 2 mg dose produced an intracortical disinhibition and enhanced intracortical facilitation. These changes returned to baseline after 24 h. Other electrophysiological parameters remained unchanged. Thus, an antagonist of pre- and postsynaptic muscarinic receptors increased excitability in the human motor cortex in a dose-dependent manner, indicating an influence of the cholinergic system on motor cortex excitation.

Administration, Oral↗

PubMed2006

Modulatory effects of 1 Hz rTMS over the cerebellum on motor cortex excitability.

Clinical observations and data from animal experiments point to a physiological facilitatory influence of the deep cerebellar structures on the motor system through the cerebello-thalamo-cortical pathways. The aim of the present study was to explore the long-term effects of low-frequency (1 Hz) repetitive transcranial magnetic stimulation (rTMS) over the cerebellum on short intracortical inhibition (SICI) and facilitation (ICF) of the motor cortex in normal subjects. Eight healthy subjects (mean age 26.9 +/- 3.1) underwent 1 Hz frequency rTMS delivered on the right cerebellar hemisphere. Before and after cerebellar rTMS, SICI and ICF were assessed in the motor cortex contralateral to the stimulated cerebellar hemisphere by means of a paired pulse paradigm with a conditioning subthreshold stimulus set to 80% of the motor threshold (MT) followed by a testing stimulus at 120% of MT intensity. Five different interstimulus intervals (ISIs) were used to assess SICI (2 and 4 ms) and ICF (7, 10 and 15 ms). Amplitude of the responses was expressed as the percentage of motor evoked potential (MEP) to test stimulus alone. Results showed a significant decrease of ICF at 10 ms ISI that persisted up to 20 min after cerebellar rTMS. This was the only significant modulatory effect of cerebellar stimulation on intracortical motor excitability A suppressive effect of the low-frequency TMS on Purkinje cells could be supposed, even if, the lack of effects on other facilitatory ISIs, stands for more complex modulatory effects of rTMS over cerebellum. The study is a further demonstration that rTMS over the cerebellum induces a long-lasting modulatory effect on the excitability of the interconnected motor area.

Adult↗

PubMed1988

[Activation of motor pathways in neonates at term by percutaneous stimulation of the motor cortex and spinal cord].

The percutaneous stimulation of both the motor cortex and the spinal cord have been used to study the central motor pathways of 19 healthy full-term newborns and of 5 infants (17 months to 4 years). The responses of lower limb muscles to cortical stimulation were more difficult to obtain than those of upper limb muscles. Conduction velocities of central motor fibres along the spinal cord (between C7 to L4) were around 10 m/s in full-term newborns and 38 m/s at the age of 4 years old. These values are considerably less than those published in adult man (48 to 60 m/s).

Arm↗

PubMed2003

Ketamine increases human motor cortex excitability to transcranial magnetic stimulation.

Subanaesthetic doses of the N-methyl-D-aspartate (NMDA) antagonist ketamine have been shown to determine a dual modulating effect on glutamatergic transmission in experimental animals, blocking NMDA receptor activity and enhancing non-NMDA transmission through an increase in the release of endogenous glutamate. Little is known about the effects of ketamine on the excitability of the human central nervous system. The effects of subanaesthetic, graded incremental doses of ketamine (0.01, 0.02 and 0.04 mg kg-1 min-1, I.V.) on the excitability of cortical networks of the human motor cortex were examined with a range of transcranial magnetic and electric stimulation protocols in seven normal subjects. Administration of ketamine at increasing doses produced a progressive reduction in the mean resting motor threshold (RMT) (F(3, 18) = 22.33, P < 0.001) and active motor threshold (AMT) (F(3, 18) = 12.17, P < 0.001). Before ketamine administration, mean RMT +/- S.D. was 49 +/- 3.3 % of maximum stimulator output and at the highest infusion level it was 42.6 +/- 2.6 % (P < 0.001). Before ketamine administration, AMT +/- S.D. was 38 +/- 3.3 % of maximum stimulator output and at the highest infusion level it was 33 +/- 4.4 % (P < 0.002). Ketamine also led to an increase in the amplitude of EMG responses evoked by magnetic stimulation at rest; this increase was a function of ketamine dosage (F(3, 18) = 5.29, P = 0.009). In contrast to responses evoked by magnetic stimulation, responses evoked by electric stimulation were not modified by ketamine. The differential effect of ketamine on responses evoked by magnetic and electric stimulation demonstrates that subanaesthetic doses of ketamine enhance the recruitment of excitatory cortical networks in motor cortex. Transcranial magnetic stimulation produces a high-frequency repetitive discharge of pyramidal neurones and for this reason probably depends mostly on short-lasting AMPA transmission. An increase in this transmission might facilitate the repetitive discharge of pyramidal cells after transcranial magnetic stimulation which, in turn, results in larger motor responses and lower thresholds. We suggest that the enhancement of human motor cortex excitability to transcranial magnetic stimulation is the effect of an increase in glutamatergic transmission at non-NMDA receptors similar to that described in experimental studies.

Adult↗

PubMed1995

Changes in motor cortex activity during reaching movements with similar hand paths but different arm postures.

1. Neuronal activity was recorded in the motor cortex of a monkey that performed reaching movements with the use of two different arm postures. In the first posture (control), the monkey used its natural arm orientation, approximately in the sagittal plane. In the second posture (abducted), the monkey had to adduct its elbow nearly to shoulder level to grasp the handle. The path of the hand between targets was similar in both arm postures, but the joint kinematics and kinetics were different. 2. In both postures, the activity of single cells was often broadly tuned with movement direction and static arm posture over the targets. In a large proportion of cells, either the level of tonic activity, the directional tuning, or both, varied between the two postures during the movement and target hold periods. 3. For most directions of movement, there was a statistically significant difference in the direction of the population vector for the two arm postures. Furthermore, whereas the population vector tended to point in the direction of movement for the control posture, there was a poorer correspondence between the direction of movement and the population vector for the abducted posture. These observed changes are inconsistent with the notion that the motor cortex encodes purely hand trajectory in space.

Animals↗

PubMed1997

Persistent mirror movements: functional MR imaging of the hand motor cortex.

PURPOSE: To compare cortical areas involved in hand motor function in patients with persistent motor movements with those in healthy control subjects by using functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: Nine patients (five patients with autosomal-dominant mirror movements, three with Kallmann syndrome, one with Wildervanck syndrome) and 10 healthy control subjects participated in the study. Functional MR imaging was performed at 1.5 T with a two-dimensional fast low-angle shot sequence. Participants were imaged while performing sequential finger-thumb opposition and during a rest period. RESULTS: During unimanual intentional movements, MR imaging in all control subjects showed increased signal intensity along the superior bend of the central sulcus contralateral to the moved hand. This increase was predominantly located in a region that included the medial part of the precentral gyrus. In contrast, MR imaging in patients with mirror movements showed bilateral activity in the medial region of the precentral gyrus. CONCLUSION: Bifurcations of the corticospinal tract may not be solely responsible for mirror movements. Bilateral activity of the primary motor cortex seems to play an additional role.

Adolescent↗

PubMed1999

Distribution and latency of muscle responses to transcranial magnetic stimulation of motor cortex after spinal cord injury in humans.

Noninvasive transcranial magnetic stimulation (TMS) of the motor cortex was used to evoke electromyographic (EMG) responses in persons with spinal cord injury (n = 97) and able-bodied subjects (n = 20, for comparative data). Our goal was to evaluate, for different levels and severity of spinal cord injury, potential differences in the distribution and latency of motor responses in a large sample of muscles affected by the injury. The spinal cord injury (SCI) population was divided into subgroups based upon injury location (cervical, thoracic, and thoracolumbar) and clinical status (motor-complete versus motor-incomplete). Cortical stimuli were delivered while subjects attempted to contract individual muscles, in order to both maximize the probability of a response to TMS and minimize the response latency. Subjects with motor-incomplete injuries to the cervical or thoracic spinal cord were more likely to demonstrate volitional and TMS-evoked contractions in muscles controlling their foot and ankle (i.e., distal lower limb muscles) compared to muscles of the thigh (i.e., proximal lower limb muscles). When TMS did evoke responses in muscles innervated at levels caudal to the spinal cord lesion, response latencies of muscles in the lower limbs were delayed equally for persons with injury to the cervical or thoracic spinal cord, suggesting normal central motor conduction velocity in motor axons caudal to the lesion. In fact, motor response distribution and latencies were essentially indistinguishable for injuries to the cervical or thoracic (at or rostral to T10) levels of the spine. In contrast, motor-incomplete SCI subjects with injuries at the thoracolumbar level showed a higher probability of preserved volitional movements and TMS-evoked contractions in proximal muscles of the lower limb, and absent responses in distal muscles. When responses to TMS were seen in this group, the latencies were not significantly longer than those of able-bodied (AB) subjects, strongly suggestive of "root sparing" as a basis for motor function in subjects with injury at or caudal to the T11 vertebral body. Both the distribution and latency of TMS-evoked responses are consistent with highly focal lesions to the spinal cord in the subjects examined. The pattern of preserved responsiveness predominating in the distal leg muscles is consistent with a greater role of corticospinal tract innervation of these muscles compared to more proximal muscles of the thigh and hip.

Adolescent↗

PubMed2005

Extradural motor cortex stimulation in advanced Parkinson's disease: the Turin experience: technical case report.

OBJECTIVE AND IMPORTANCE: At our institution, extradural motor cortex stimulation (EMCS) has recently been applied for treating Parkinson's disease symptoms. We report our results and review the literature supporting this application of EMCS. CLINICAL PRESENTATION: Since 1998, six patients affected by advanced Parkinson's disease and not fulfilling inclusion criteria for deep brain stimulation underwent EMCS. INTERVENTION: A quadripolar electrode was introduced in the extradural space over the motor cortex, opposite to the side on which parkinsonian symptoms had begun. Bipolar chronic electrostimulation was delivered at 2.5 to 6 V, 150 to 180 microseconds, and 25 to 40 Hz. Preoperative and postoperative clinical status was assessed by the Unified Parkinson's Disease Rating Scale (UPDRS) and recorded on videotapes. The follow-up of this series varied from 4 months to 2.5 years. After EMCS, the overall UPDRS score decreased by 42 to 62%; Section III UPDRS score (motility evaluation) by 32 to 83%; and Section IV UPDRS score (therapy complications) by 100% in two patients, by 50 to 67% in four patients, and by 33% in one patient. L-Dopa therapy was reduced by 11 to 33% in three patients and by 70 to 73% in the other two patients. No postoperative complications or negative side effects of electrostimulation were recorded, except for a misplacement of the electrodes in one patient. CONCLUSION: Unilateral EMCS relieves, at least partially, but sometimes dramatically, the whole spectrum of symptoms in advanced Parkinson's disease. L-Dopa may be reduced up to 70%. The symptoms of long-term L-dopa syndrome are usually markedly improved. The neurophysiological mechanisms involved are still under debate. Our clinical experience adds favorable data to enlarge the series of parkinsonian patients treated by EMCS.

Aged↗