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PubMed1998

Modulation of ipsilateral motor cortex in man during unimanual finger movements of different complexities.

To understand the role of the ipsilateral motor cortex in the control of unimanual movements, we evaluated changes in cortical motor evoked potentials (MEP) from the left abductor pollici brevis (APB) to transcranial magnetic stimulation (TMS) of the right hemisphere in nine normal subjects during execution of right finger movements of different complexities. The motor tasks were (a) repetitive opposition movement (thumb tapping the 3rd finger); (b) isolated finger movements in a 'usual' sequence (thumb tapping fingers 2, 3, 4 and 5) and (c) in an 'unusual' sequence (thumb tapping fingers 3, 5, 2 and 4). Subjects were trained before the study up to disappearance of EMG synkinetic activity in the left APB. As compared to the rest condition, MEP amplitude was enhanced in all subjects during paradigm (b) and even more during (c), but remained unchanged during paradigm (a). The MEP increase disappeared in four out of the nine subjects undergoing overtraining. No significant modifications in MEP amplitude were found in the left proximal muscle (biceps, five subjects). The H reflex induced by left median nerve stimulation at the elbow (four subjects) and MEPs from the left APB to transcranial electrical stimulation (three subjects) were not significantly affected by any of the motor paradigms, indicating that the motor cortex was the site of change. These results provide evidence of an increased excitability of cortical motor outputs targeting the unmoving hand muscles during contralateral sequential finger movements which disappears with overtraining. We conclude that during motor learning there is an interhemispheric transfer of information, possibly in order to inhibit the opposite hemisphere from interfering when a fine unimanual movement is required.

Adult↗
PubMed1998

Demonstration of facilitatory I wave interaction in the human motor cortex by paired transcranial magnetic stimulation.

1. Transcranial magnetic stimulation (TMS) of the human motor cortex results in multiple discharges (D and I waves) in the corticospinal tract. We tested whether these volleys can be explored non-invasively with paired TMS. The intensity of the first stimulus (S1) was set to produce a motor-evoked potential (MEP) of 1 mV in the resting contralateral abductor digiti minimi (ADM) muscle; the second stimulus (S2) was set to 90 % of the resting motor threshold. At interstimulus intervals of 1.1-1.5, 2.3-2.9 and 4.1-4.4 ms the MEP elicited by S1 plus S2 was larger than that produced by S1 alone. 2. Varying the S1 intensity between 70 and 130 % resting motor threshold with S2 held constant at 90 % resting motor threshold showed that the threshold for the first MEP peak was <= 70 % resting motor threshold. The second and third MEP peaks appeared only at higher S1 intensities. The latency of all peaks decreased with increasing S1 intensity. 3. Varying the S2 intensity with S1 held constant to produce a MEP of 1 mV on its own showed that the amplitude of all MEP peaks increased with S2 intensity, but that their timing remained unchanged. 4. Paired TMS in the active ADM (S1 clearly suprathreshold, S2 just above threshold; interstimulus interval, 1 ms) produced strong MEP facilitation. The onset of this facilitation occurred later by about 1.5 ms than the onset of the MEP evoked by S2 alone. No MEP facilitation was seen if the magnetic S2 was replaced by anodal or cathodal transcranial electrical stimulation. 5. It is concluded that the MEP facilitation after paired TMS, at least for the first MEP peak, is due to facilitatory interaction between I waves, and takes place in the motor cortex at or upstream from the corticospinal neurone.

Adult↗
PubMed2005

The effect of tumour type and distance on activation in the motor cortex.

Functional MRI has been widely used to identify the eloquent cortex in neurosurgical/radiosurgical planning and treatment of CNS neoplasms and malformations. In this study we examined the effect of CNS tumours on the blood oxygenation level-dependent (BOLD) activation maps in the primary and supplementary motor cortex. A total of 33 tumour patients and five healthy right-handed adults were enrolled in the study. Patients were divided into four groups based on tumour type and distance from primary motor cortex: (1) intra-axial, near, (2) extra-axial, near, (3) intra-axial, far and (4) extra-axial, far. The intra-axial groups consisted of patients with astrocytomas, glioblastomas and metastatic tumours of mixed histology; all the extra-axial tumours were meningiomas. The motor task was a bilateral, self-paced, finger-tapping paradigm. Anatomical and functional data were acquired with a 1.5 T GE Echospeed scanner. Maps of the motor areas were derived from the BOLD images, using SPM99 software. For each subject we first determined the activation volume in the primary motor area and the supplementary motor area (SMA) and then calculated the percentage difference between the hemispheres. Two factors influenced the activation volumes: tumour type (P<0.04) and distance from the eloquent cortex (P<0.06). Patients in group 1 (intra-axial, near) had the smallest activation area in the primary motor cortex, the greatest percentage difference in the activation volume between the hemispheres, and the largest activation volume in the SMA. Patients in group 4 (extra-axial, far) had the largest activation volume in the primary motor cortex, the least percentage difference in volume between the hemispheres, and the smallest activation volume in the SMA. There was no significant change in the volume of the SMA in any group, compared with controls, suggesting that, although there is a gradual decrease in SMA volume with distance from the primary motor area, the effect on motor reorganisation is minimal. All the tumour patients showed a net loss in total activation volumes (both hemispheres plus SMA) compared with controls. The effect of the tumours on interhemispheric volume differences was: group 1>group 3>group 2>group 4. Within the intra-axial tumours, there was no significant effect of tumour type on the results. We conclude that BOLD-imaged activation volume is affected at least by the interplay of two factors: tumour type and distance from the motor cortex. Further, all tumours may be expected to cause some loss of activation volumes in motor areas. We suggest that, with proper precautions and planning, BOLD functional magnetic resonance imaging (fMRI) maps can be useful in minimising damage to the functional areas.

Adult↗
PubMed2003

Functional organization of adult motor cortex is dependent upon continued protein synthesis.

The functional organization of adult cerebral cortex is characterized by the presence of highly ordered sensory and motor maps. Despite their archetypical organization, the maps maintain the capacity to rapidly reorganize, suggesting that the neural circuitry underlying cortical representations is inherently plastic. Here we show that the circuitry supporting motor maps is dependent upon continued protein synthesis. Injections of two different protein synthesis inhibitors into adult rat forelimb motor cortex caused an immediate and enduring loss of movement representations. The disappearance of the motor map was accompanied by a significant reduction in synapse number, synapse size, and cortical field potentials and caused skilled forelimb movement impairments. Further, motor skill training led to a reappearance of movement representations. We propose that the circuitry of adult motor cortex is perpetually labile and requires continued protein synthesis in order to maintain its functional organization.

Age Factors↗
PubMed1996

Intraoperative localisation of the primary motor cortex using single electrical stimuli.

A new method of intraoperative localisation of the primary motor cortex is described, based on the application of single anodal electric pulses to the brain surface. Patients were anaesthetised with propofol infusion, and neuromuscular blockade was temporarily alleviated to allow recording of surface EMG responses (CMAPs) to the stimuli. Primary motor areas could be localised in 18/19 patients studied. In the other patient, no responses were elicited, as the operative field was posterior to the motor cortex. When compared with MEPs elicited in awake patients by magnetic stimuli, responses to intraoperative anodal stimulation were of small amplitude (usually less than 10% of MEPs) and their latency was some 1 to 2 ms longer. One month after the operation, only 1/19 patients was left with a slight muscle weakness, although seven showed preoperative motor deficit. The procedure proved easy and fast, needing no preliminary surgery or time consuming preparation. It did not induce any detectable side effects.

Brain Mapping↗
PubMedDate not supplied

[Effect of the motor cortex on heterogeneous afferent flows in the mediodorsal nucleus of the thalamus].

In experiments carried out on cats anaesthetized with Nembutal evoked potentials were recorded in the thalamic mediodorsal (MD) nucleus and in the projection and motor cortical areas with local cooling of the latter and the use of either single or paired stimuli of the same or different modalities. Visual and somatic excitatory inflows to the MD have been established, involving signals of specific and reticular genesis. Coming by separate ways they form isolated populations of neurones in the MD. A facilitating modulating influence of MD has been defined on the realization of afferent bursts produced in the motor cortex by visual and, particularly, somatic stimuli. It was found that in spite of its polyfunctionality, the motor cortex specifically influences heterogeneous inflows to the MD, exerting a more intensive and different action on the somatic afferentation as compared with the visual one. It is assumed that the specific and direct influence of the motor cortex on these impulses is exercised due to a functional subdivision of its corticofugal pathway into separate subsystems.

Animals↗
PubMed1990

Modulation of neuronal activities by iontophoretically applied catecholamines and acetylcholine in the primate motor cortex during a visual reaction-time task.

Single neuronal activities in the primate motor cortex were modulated by iontophoretically applied acetylcholine (ACh), noradrenaline (NA) or dopamine (DA) while monkeys were performing a visual reaction-time. task. ACh caused general increases of the discharge activities of both the background baseline and the task-related activity peaks, whereas NA caused decreases mainly of the baseline. DA caused activity increases in half of the tested neurons, and decreases in 25% of the neurons. NA modulated the firing rate to enhance the signal-to-noise ratio of the related activities. ACh and DA, by contrast, subserved to enhance the synaptic transmission in the motor cortex.

Acetylcholine↗
PubMed1987

Activation of the human diaphragm from the motor cortex.

1. Rapidly conducting corticofugal pathways were activated by percutaneous electrical stimulation of the motor cortex in normal subjects. The electromyographic response produced in the diaphragm was assessed with recordings via a gastro-oesophageal catheter and the mechanical response was measured as a change in transdiaphragmatic pressure. 2. The mean latency from the cortical stimulus to the muscle action potential in the diaphragm was 12.3 ms. The latency to the diaphragm from stimulation of the cervical spinal cord at the C4 level was 8.0 ms. The mean 'central conduction time' to the phrenic motor nucleus of 4.3 ms (range 4.0-4.6 ms) was similar to that for the deltoid (mean 4.4 ms; range 4.0-4.8 ms) recorded in the same subjects. 3. The largest twitch contractions of the diaphragm were evoked by cortical stimuli near the vertex during inspiration. The amplitude and duration of the electromyographic and mechanical responses often exceeded those produced by a supramaximal stimulus to both phrenic nerves simultaneously. 4. These results provide the first direct evidence that there is a rapidly conducting oligosynaptic pathway from the motor cortex to the human diaphragm.

Action Potentials↗
PubMed2005

[Motor cortex stimulation for Parkinson's disease and dystonia: lessons from transcranial magnetic stimulation? A review of the literature].

INTRODUCTION: Over the last few years, deep brain stimulation techniques, with targets such as the subthalamic nucleus or the pallidum, have bee found to be beneficial in the treatment of Parkinson's disease and dystonia. Conversely, therapeutic strategies of cortical stimulation have not yet been validated in these diseases, although they are known to be associated with various cortical dysfunctions. Transcranial magnetic stimulation (TMS) is a valuable tool for non-invasive study of the role played by the motor cortex in the pathophysiology of movement disorders, in particular by assessing various cortical excitability determinants using single or paired pulse paradigms. In addition, repetitive TMS (rTMS) trains can be used to study the effects of transient activity changes of a targeted cortical area. BACKGROUND: Studies with TMS revealed significant motor cortex excitability changes, particularly regarding intracortical inhibitory pathways, both in Parkinson's disease and in dystonia, and these changes can be distinguished owing to the resting state or to the phases of movement preparation or execution. However, more specific correlation between electrophysiological features and clinical symptoms remains to be established. In addition, the stimulation of various cortical targets by rTMS protocols applied at low or high frequencies have induced some clear clinical effects. PERSPECTIVES: The TMS effects are and will remain applied in movement disorders to better understand the role played by the motor cortex, to assess various types of treatment and appraise the therapeutic potential of cortical stimulation. CONCLUSION: TMS provides evidence for motor cortex dysfunction in Parkinson's disease or dystonia. Moreover, rTMS results have opened new perspectives for therapeutic strategies of implanted cortical stimulation. By these both aspects, TMS techniques show their usefulness in the assessment of movement disorders.

Deep Brain Stimulation↗
PubMed1994

Differential contribution of motor cortex and caudate nucleus to instrumental tongue-forelimb synchronization in rats: a functional ablation study.

The functional ablation technique was used to assess the role of motor cortex and caudate nucleus in a complex skilled movement. Rats were trained to synchronize tongue and forepaw movements in a drinking box equipped with a retractable spout which was automatically withdrawn after every lick but could be returned by pressing and releasing a lever placed 4 cm below the spout. The animals learned to perform short presses synchronized with the lick cycle in such a way as to allow continuous drinking. Neural circuits implementing these lick-associated instrumental movements were blocked by intracranial injection of 10 ng of tetrodotoxin. Bilateral blockade of the motor cortex interfered with lick-synchronized bar pressing, but did not significantly influence licking from a stationary spout. Both licking and bar-pressing were impaired by bilateral injection of tetrodotoxin into the lateral part of the caudate nucleus for the duration of the tetrodotoxin-induced inactivation of the target region. The instrumental tongue-forelimb synchronization recovered considerably later, i.e. after two to three days. Functional blockade of the medial part of the caudate nucleus caused only a partial impairment of lick-synchronized bar pressing lasting less than 7 h and did not significantly influence consummatory licking. It is concluded that the tongue-forepaw synchronization is disrupted by blockade of motor cortex or lateral caudate considerably longer than the performance of the isolated component movements.

Animals↗
PubMed2000

Motor cortex excitability in stiff-person syndrome.

Muscle stiffness in stiff-person syndrome (SPS) is produced by continuous, involuntary firing of motor units that is thought to be caused by an autoimmune mediated dysfunction of GABA-ergic inhibitory neurones. We have postulated that the loss of GABA-ergic inputs from spinal interneurones alone is insufficient to produce tonic firing of motor neurones and that excessive supraspinal excitation could also play a role. To determine whether SPS is associated with dysfunction in supraspinal GABA-ergic neurones, we assessed the excitability of the motor cortex with transcranial magnetic stimulation (TMS) in seven SPS patients and seven age-matched healthy volunteers. SPS patients had normal central motor conduction times, normal thresholds for motor evoked potentials (MEPs) in leg muscles, and a normal MEP stimulus versus response recruitment curve with increasing TMS intensities in resting hand and leg muscles. Cortical silent periods were shortened in leg muscles. Intracortical inhibition and excitation were assessed while recording from the abductor pollicis brevis, using a paired pulse TMS paradigm with subthreshold conditioning stimuli. Patients had decreased inhibition and markedly increased facilitation at short intervals. Using paired suprathreshold TMS, patients exhibited increased facilitation at 20- and 40-ms intervals. These results point to a hyperexcitability of the motor cortex in SPS, which could be explained by impairment of supraspinal GABA-ergic neurones, leading to an impaired balance between inhibitory and excitatory intracortical circuitry.

Action Potentials↗
PubMed1991

Functional organization of human supplementary motor cortex studied by electrical stimulation.

The presence of somatotopic organization in the human supplementary motor area (SMA) remains a controversial issue. In this study, subdural electrode grids were placed on the medial surface of the cerebral hemispheres in 13 patients with intractable epilepsy undergoing evaluation for surgical treatment. Electrical stimulation mapping with currents below the threshold of afterdischarges showed somatotopic organization of supplementary motor cortex with the lower extremities represented posteriorly, head and face most anteriorly, and the upper extremities between these two regions. Electrical stimulation often elicited synergistic and complex movements involving more than one joint. In transitional areas between neighboring somatotopic representations, stimulation evoked combined movements involving the body parts represented in these adjacent regions. Anterior to the supplementary motor representation of the face, vocalization and speech arrest or slowing of speech were evoked. Various sensations were elicited by electrical stimulation of SMA. In some cases a preliminary sensation of "urge" to perform a movement or anticipation that a movement was about to occur were evoked. Most responses were contralateral to the stimulated hemisphere. Ipsilateral and bilateral responses were elicited almost exclusively from the right (nondominant) hemisphere. These data suggest the presence of combined somatotopic organization and left-right specialization in human supplementary motor cortex.

Adolescent↗
PubMed1994

Functional 2D and 3D magnetic resonance imaging of motor cortex stimulation at high spatial resolution using standard 1.5 T imager.

This paper reports the effects of motor cortex stimulation of normal volunteers using conventional MR imaging techniques on standard 1.5 T clinical scanner. Improvement in signal-to-noise (S/N) ratio has been achieved by using a commercially available eye/ear surface coil with a loop of 8.5 cm in diameter. Magnet shimming with all first order coils was performed to the volunteer's head resulting in a magnetic field homogeneity of about 0.1-0.2 ppm. The imaging technique used was an optimized conventional 2D and 3D, first order flow rephased, gradient-echo sequence (FLASH) with fat-suppression and reduced bandwidth (16-28 Hz/pixel) and TR = 80-120 ms, TE = 60 ms, flip angle = 40 degrees, matrix = 128 x 128, FOV = 150-250 mm, slice-thickness = 2-5 mm, NEX = 1, and a total single scan time for one image of about 12-16 s. In the 3D FLASH measurements, a slab of 32 mm thickness with 16 partitions was evaluated. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. During stimulation, an increase in signal of order 10-20% was detected in the motor and sensory cortex due to reduced partial volume effects and optimized S/N for the measurements at small voxel size. 3D FLASH imaging at high spatial resolution shows good anatomical correlation of signal increase with gray matter of the motor and sensory cortex. The reported data demonstrate the technical feasibility of functional 2D and 3D MR imaging at high spatial resolution using optimized conventional sequences and equipment.

Humans↗
PubMed1987

Evaluations of combined premotor and supplementary motor cortex lesions on a visually guided arm movement.

The kinematics of a visually guided, multi-joint arm movement were examined before and after combined bilateral premotor and supplementary motor cortex lesions. Two rhesus monkeys were trained to move a manipulandum from a start zone to one of three equally spaced target zones and then return to the initial start zone. Various features of the movement trajectory including space error, time error, peak velocity and turnaround time were quantified and analyzed before and after the premotor and supplementary motor cortex ablations. Statistical analysis showed no major differences in the trajectories toward or away from the target between the pre- and postlesion state. The major difference following the ablation was an increase in the time spent in the target zone, reflecting an increase in time spent in redirecting the trajectory. Normalization of the movement duration revealed a slight delay in the initial part of the movement. These results suggest the premotor and supplementary motor cortex are involved in redirecting the trajectory and/or obtaining the target zone during the execution of a complex movement.

Animals↗