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Results for “Motor Cortex”

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PubMed2005

Repetitive transcranial magnetic stimulation of contralesional primary motor cortex improves hand function after stroke.

BACKGROUND AND PURPOSE: A recent report has demonstrated that the contralesional primary motor cortex (M1) inhibited the ipsilesional M1 via an abnormal transcallosal inhibition (TCI) in stroke patients. We studied whether a decreased excitability of the contralesional M1 induced by 1 Hz repetitive transcranial magnetic stimulation (rTMS) caused an improved motor performance of the affected hand in stroke patients by releasing the TCI. METHODS: We conducted a double-blind study of real versus sham rTMS in stroke patients. After patients had well- performed motor training to minimize the possibility of motor training during the motor measurement, they were randomly assigned to receive a subthreshold rTMS at the contralesional M1 (1 Hz, 25 minutes) or sham stimulation. RESULTS: When compared with sham stimulation, rTMS reduced the amplitude of motor-evoked potentials in contralesional M1 and the TCI duration, and rTMS immediately induced an improvement in pinch acceleration of the affected hand, although a plateau in motor performance had been reached by the previous motor training. This improvement in motor function after rTMS was significantly correlated with a reduced TCI duration. CONCLUSIONS: We have demonstrated that a disruption of the TCI by the contralesional M1 virtual lesion caused a paradoxical functional facilitation of the affected hand in stroke patients; this suggests a new neurorehabilitative strategy for stroke patients.

Adult↗

PubMed1998

Paired-pulse magnetic stimulation of the human motor cortex: differences among I waves.

1. In paired-pulse cortical stimulation experiments, conditioning subthreshold stimuli suppress the electromyographic (EMG) responses of relaxed muscles to suprathreshold magnetic test stimuli at short interstimulus intervals (ISIs) (1-5 ms) and facilitate them at long ISIs (8-15 ms). 2. We made paired-pulse magnetic stimulation studies on the response of the first dorsal interosseous muscle (FDI) produced by I1 or I3 waves using our previously reported method which preferentially elicits one group of I waves when subjects make a slight voluntary contraction. In some experiments the conditioning and test stimuli were oppositely directed, in the others they were oriented in the same direction. Single motor unit responses were recorded with a concentric needle electrode, and surface EMG responses with cup electrodes. 3. In post-stimulus time histograms (PSTHs) of the firing probability of motor units, the peaks produced by I3 waves were decreased by a subthreshold conditioning stimulus that preferentially elicited I1 or I3 waves at an ISI of 4 ms. The amount of decrement depended on the intensity of the conditioning stimulus. The stronger the conditioning stimulus, the greater the suppression. In contrast, the peaks produced by I1 waves were little affected by any type of subthreshold conditioning stimulus, given 4 ms prior to the test stimulus. At an ISI of 10 ms, a subthreshold conditioning stimulus slightly decreased the size of the peak produced by the I3 waves, but did not affect the peaks evoked by I1 waves. 4. Surface EMGs showed that a subthreshold conditioning stimulus suppressed the responses produced by I3 waves irrespective of its current direction (anterior or posterior). Both the amount and duration of suppression depended on the intensity of the conditioning stimulus, but not on its current direction. Both parameters increased when the intensity increased. At a high intensity conditioning stimulus, suppression was evoked at ISIs of 1-20 ms, compatible with the duration of GABA-mediated inhibition found in animal experiments. Responses produced by I1 waves were little affected by any type of subthreshold conditioning stimulus. 5. We conclude that a subthreshold conditioning stimulus given over the motor cortex moderately suppresses I3 waves but does not affect I1 waves. The duration of suppression of the I3 waves supports the idea that this is an effect of GABAergic inhibition within the motor cortex.

Adult↗

PubMed2002

Motor cortex extirpation (1886-1950): the influence of Sir Victor Horsley.

OBJECTIVE: To delineate Sir Victor Horsley's influence on neurosurgeons who subsequently reported (through 1950) on the effects of motor cortex extirpation surgery. METHODS: We used the available literature to divide Horsley's influence into five categories, i.e., direct trainee, via a trainee or colleague, via personal contact and publications, via publications only, and no evidence of influence. RESULTS: Of 15 later neurosurgeons who reported results through 1950, the numbers corresponding to the five categories were 1, 6, 2, 3, and 3, respectively. CONCLUSION: Horsley's influence on neurosurgeons who performed motor cortex extirpation surgery was primarily indirect, with most influence occurring via trainees of his students or colleagues. Although indirectly associated with Horsley, Paul Bucy was his truest disciple.

History, 20th Century↗

PubMed2005

Frequency specific changes in regional cerebral blood flow and motor system connectivity following rTMS to the primary motor cortex.

Repetitive transcranial magnetic stimulation (rTMS) to the human primary motor cortex (M1) causes bidirectional changes in corticospinal excitability depending on the stimulation frequency used. We used functional brain imaging to compare the effects of 5 Hz and 1 Hz-rTMS on local and inter-regional connectivity within the motor system. Regional cerebral blood flow (rCBF) was measured as a marker of synaptic activity at rest and during freely selected finger movements. We hypothesized that increased cortical excitability induced by 5 Hz-rTMS over M1 has an opposite effect on the synaptic activity and the connectivity of the motor network from the decreased cortical excitability induced by 1 Hz-rTMS. rTMS at both frequencies induced similar changes in rCBF at the site of stimulation and within areas of the motor network engaged by the task. The two frequencies showed different effects on movement-related coupling between motor areas. Connectivity analyses also indicated a differential effect of 5 and 1 Hz-rTMS on motor network connectivity, suggesting a role for an inferomedial portion of left M1 and left dorsal premotor cortex in maintaining performance. These results suggest that rapid reorganization of the motor system occurs to maintain task performance during periods of altered cortical excitability. This reorganization differs according to the modulation of excitability which is a function of rTMS frequency. This study extends the work of Lee et al. (Lee, L., Siebner, H.R., Rowe, J.B., Rizzo, V. Rothwell, J.C. Frackowiak, R.S. Friston, K.J., 2003. Acute remapping within the motor system induced by low-frequency repetitive transcranial magnetic stimulation. J. Neurosci. 23, 5308-5318.) by providing evidence that the pattern of acute reorganization in the motor network following rTMS depends on the direction of conditioning.

Adult↗

PubMed1996

Linear estimation discriminates midline sources and a motor cortex contribution to the readiness potential.

Spatiotemporal dipole modelling of the generators of the readiness potential (RP) prior to voluntary movements has yielded diverging results concerning the contributions of supplementary motor area (SMA) and primary motor cortex. We applied an alternative approach (i.e. linear estimation theory) to measurements of the RP preceding fixed and freely selected finger movements, measured at 28 electrodes of the extended 10-20 system. The volume conductor properties of the head were modelled by 3 concentric spheres. Current densities were reconstructed on a spherical surface, placed at a depth of 5 mm from the inside of the skull. Lead field normalization was applied. The analysis shows activity on the midline as well as near the primary motor area. Although some features of the reconstructions are not readily interpretable, separate contributions of midline sources (including presumably SMA) and motor cortex to the RP are clearly distinguished.

Adult↗

PubMed1980

[Features of metabolism in subcellular fractions of the motor cortex during restoration of visual nerve impulses].

Experimental data are obtained on cytochromoxidase (CO), acetylcholinesterase (AchE), MAO and ATPase activities in subfractions of synaptosomes and cellular mitochondria from the rabbit motor cortex following long-term visual deprivation. The first stage is characterized by elevated protein content and activation of enzymatic systems except K+; Na+--ATPase and CO. The tendency towards normalizing of protein content and activity of enzymes, particularly AchE and MAO occurred within 4 weeks. These data show that changes of enzymatic activity in subcellular components of the motor cortex following the sensory deprivation, are reversible but the process of neuronal recompensation in the integrative--starting system is complex and demands a longer time than in visual one.

Acetylcholinesterase↗

PubMed2005

Motor cortex excitability and fatigue in multiple sclerosis: a transcranial magnetic stimulation study.

We investigated electrophysiological correlates of fatigue in patients with multiple sclerosis (MS). Transcranial magnetic stimulation (TMS) was used to explore motor excitability in three groups of subjects: MS patients with fatigue (MS-F), MS patients without fatigue (MS-NF) and healthy control subjects. All participants had to perform a fatiguing hand-grip exercise. TMS was performed prior to and after the exercise. Prior to the motor task, MS-F patients had less inhibition in the primary motor cortex compared to both other groups. Postexercise, intracortical inhibition was still reduced in the MS-F patients compared to the MS-NF patients. In MS-F patients the postexercise time interval for normalization of the motor threshold was correlated with the fatigue severity. We conclude that MS patients with fatigue have an impairment of inhibitory circuits in their primary motor cortex. The results also indicate that fatigue severity is associated with an exercise-induced reduction of membrane excitability.

Adult↗

PubMed2003

Synchronization in monkey motor cortex during a precision grip task. II. effect of oscillatory activity on corticospinal output.

Recordings from primary motor cortex (M1) during periods of steady contraction show oscillatory activity; these oscillations are coherent with the activity of contralateral muscles. We investigated synchronization of corticospinal output neurons with the oscillations, which could provide the pathway for their transmission to the spinal motoneurons. One hundred seventy-six antidromically identified pyramidal tract neurons (PTNs) were recorded from M1 in three macaque monkeys trained to perform a precision grip task. Local field potentials (LFP) were simultaneously recorded. All analysis was confined to the hold period of the task, where our previous work has shown that there is the strongest oscillatory activity. Coherence was calculated between LFP and PTN discharge. Significant coherence was seen in three bands, with frequencies of 10-14, 17-31, and 34-44 Hz. Coherence values were low, with the majority of PTN-LFP coherences having a peak lower than 0.05. The phase of coherence was approximately -pi/2 radians for each band (with LFP polarity defined as negative upward), although there was some dispersion of phase across the population of PTNs. Coherence was also calculated between pairs of PTNs that had been simultaneously recorded. Where there was significant coherence, it was also generally smaller than 0.05. The phase of PTN-PTN coherence clustered around zero radians. A computer model was constructed to assist the interpretation of the experimental results. It simulated an integrate-and-fire neuron responding to synaptic inputs. A fraction of the synaptic inputs was synchronized with a simulated LFP; the remainder were uncorrelated with it. The model showed that coherence between the LFP and the output spike train considerably underestimated the fraction of synchronized inputs. Additionally, for a given fraction of synchronized inputs, coherence was smaller for high- compared with low-frequency bins. Cell discharge rate also influenced the spike-LFP coherence: coherence was higher for simulations in which the cell discharged at a faster rate. Thus although levels of PTN-LFP coherence seen experimentally were low, a considerable proportion of the input to the PTN must be synchronized with the global oscillatory activity recorded by the LFP. The low LFP-PTN coherences do however indicate that cortical oscillations are transmitted with only low fidelity in the discharge of a single PTN. Using further computer simulations, it was demonstrated that a small population of PTNs could encode the cortical oscillatory signal effectively, since the action of averaging across the population improves the signal:noise ratio. The oscillations will therefore be effectively transmitted to spinal motoneurons, and this has important consequences for the possible role of oscillations in motor control of the hand.

Animals↗

PubMed1988

Changes in motor cortex neural discharge associated with the development of cerebellar limb ataxia.

1. The relation between changes in motor cortex neural (MCN) discharge and the development of limb ataxia during cerebellar dysfunction was studied in 4 Cebus monkeys. Elbow movements with decreased accelerations or with tremor were produced by reversible cerebellar nuclear cooling. Discharge from 160 neurons was analyzed in detail. 2. During cerebellar cooling 37 of 80 neurons that discharged before movement onset decreased their phasic, but not their tonic, activity. This could not be explained by decreased peak velocities during cerebellar cooling. It is suggested that this decreased phasic discharge is related to the less abrupt onset and smaller magnitude of agonist EMG activity, and to the decreased initial accelerations, without decreased peak velocities, observed in limb movements during cerebellar dysfunction. This view implies that the cerebellum is involved in some way in the generation of commands to agonist alpha-motoneurons. 3. No evidence was found that 3- to 4-Hz cerebellar intention tremor is driven by a purely central oscillator. All 28 neurons that discharged strongly in relation to cerebellar tremor in movements responded strongly and reciprocally to limb perturbations. 4. A number of changes were observed during cerebellar nuclear cooling in kinematically related neural discharge associated with disordered elbow movements: an increase in discharge of some velocity- and acceleration-like neurons, a decrease in (reciprocal) inhibition, and a shift from an acceleration-like to a velocity-like discharge in some neurons. 5. Fourteen of 29 neurons with muscle-like discharge patterns discharged in a servoassistance-like manner during cerebellar dysfunction that was consistent with them contributing to tremor. 6. The results indicate that a variety of disorders, i.e., in the generation of central commands that initiate movements and in the regulation of the gain and phase of proprioceptive feedback, contribute to the development of limb ataxia during cerebellar dysfunction.

Action Potentials↗

PubMed1990

Correlation of motor cortex brain mapping data with magnetic resonance imaging.

Brain maps derived intraoperatively from patients undergoing tumor resection were correlated retrospectively with magnetic resonance (MR) images with respect to the precise localization of the motor cortex in an attempt to identify useful preoperative MR imaging landmarks that correspond to functional brain regions. Superior axial T2-weighted MR images consistently localized the central sulcus, whereas parasagittal and farlateral sagittal images readily identified the rolandic (sensorimotor) cortex, as a functional unit, based on the cingulate-marginal sulcus and insula, respectively. It is therefore concluded that multiplanar MR images may serve as a useful preoperative planning aid prior to removing intrinsic brain tumors within or adjacent to the motor cortex.

Brain Mapping↗

PubMed1998

Facilitation of a hand muscle response to stimulation of the motor cortex preceding a simple reaction task.

Transcranial magnetic stimulation (TMS) of the motor cortex was used to produce compound motor evoked potentials (cMEPs) in the first dorsal interosseus (FDI) muscle. The size of cMEPs was measured as an index of corticospinal excitability before and after initiation of a simple reaction task (SRT). The SRT, consisting of an abduction of the right index finger against a vertical support in response to a 1 kHz cueing tone, was performed in 6 healthy male subjects. cMEPs were facilitated when timed to occur just before the fastest simple reaction time (fSRT). When the cMEP was placed 15.5 +/- 1.5 ms before the fSRT, its amplitude increased to 176 +/- 36% of the control response seen in the relaxed state (no SRTs). Facilitation of the cMEP increased to 382 +/- 43% of the control when it was placed 11.9 +/- 1.5 ms after the fSRT. The facilitation of cMEP responses prior to the SRT is discussed with particular reference to the premovement potential that may be recorded over the cortex prior to a voluntary movement.

Adult↗

PubMed2006

Transcranial magnetic stimulation for pain control. Double-blind study of different frequencies against placebo, and correlation with motor cortex stimulation efficacy.

OBJECTIVE: To assess, using a double-blind procedure, the pain-relieving effects of rTMS against placebo, and their predictive value regarding the efficacy of implanted motor cortex stimulation (MCS). METHODS: Three randomised, double-blinded, 25 min sessions of focal rTMS (1 Hz, 20 Hz and sham) were performed in 12 patients, at 2 weeks intervals. Effects on pain were estimated from daily scores across 5 days before, and 6 days after each session. Analgesic effects were correlated with those of subsequent implanted motor cortex stimulation (MCS). RESULTS: Immediately after the stimulating session, pain scores were similarly decreased by all rTMS modalities. Conversely, during the following week, 1 Hz stimulation provided significantly less analgesia than 20 Hz and placebo, and was pro-algesic in some patients. Placebo and 20 Hz rTMS were effective on different patients, and only 20 Hz rTMS predicted the efficacy of subsequent MCS, with no false positives. CONCLUSIONS: While 1Hz rTMS should not be used with analgesic purposes, high-frequency rTMS may become useful to select candidates for MCS. Placebo effects are powerful and should be controlled for. Immediate results after a single rTMS session are misleading. SIGNIFICANCE: Defining rTMS parameters is a crucial step before proposing rTMS as predictive test of SCM efficacy in clinical practice.

Adult↗

PubMed1981

Characteristics of the ipsilateral movement-related neuron in the motor cortex of the monkey.

The characteristics of the precentral neuron activity related to ipsilateral movements were studied while the monkey was performing finger, wrist and arm movements on either side. Out of 197 task-related neurons, 134 discharged in association with contralateral movements, but not with any one of 3 ipsilateral movements. Fifty neurons discharged with bilateral movements. Thirteen neurons discharged in association with ipsilateral movements (ipsi-neurons). Ten were recorded from the trunk or shoulder area of the motor cortex and were accompanied by contraction of those muscles by intracortical stimulation (ICS). The remaining 3 were related to elbow or wrist, but no ipsi-neurons were related to finger muscle contractions. In ipsilateral task performance, 7 ipsi-neurons discharged in association with finger and/or wrist movements in addition to arm movement. Five others were associated with arm movement. The last one discharged with wrist movement. Most of the units showed similar response to contralateral movement. Ipsi-neurons were classified into two groups. One group was recorded around the sulcus precentralis superior, had the lower threshold current and was mostly associated with finger, wrist and arm movements. The other was recorded in the rostral motor cortex, and had the higher threshold current and was related to arm movement. Among 185 neurons to which pyramidal tract stimulation was delivered, 2 out of the 80 PTNs and 11 out of the 105 non-PTNs were ipsi-neurons. EMGs were recorded from various muscles involved in the forelimb movements. Arm and finger muscles showed no activity when the monkey used the ipsilateral hand, while most of the shoulder and trunk muscles showed tonic or moderate transient changes in the activity during the ipsilateral tasks. The ipsi-neuron activity was discussed in consideration with EMGs.

Animals↗

PubMed2003

Changes in finger coordination and responses to single pulse TMS of motor cortex during practice of a multifinger force production task.

We investigated the changes in finger coordination and in finger force responses to transcranial magnetic stimulation (TMS) applied over the motor cortex associated with a single practice session of an accurate ramp force production task. Subjects pressed with their index, middle and ring fingers onto three force transducers fixed to a rigid platform that was balanced on a narrow pivot under the middle finger. The task was to produce a smoothly increasing ramp of total force from 0 to 25 N over 4 s following a visual target. Subjects performed three brief series of trials without TMS (12 trials each) in the beginning, in the middle, and in the end of the experiment. The main part of the experiment involved 173 trials, and in each of them at random times in the ramp a suprathreshold TMS pulse was applied over the hand area of the contralateral motor cortex in order to evoke a twitch in the finger flexor muscles. At the end of the experiment the subjects also performed 12 constant force production trials, and TMS was unexpectedly applied in each trial. During the ramp force trials the amplitude of the response to TMS was largely independent of the force exerted at the time of stimulation, whereas in static holding trials the amplitude of the response increased with higher levels of background contraction. Over time subjects improved their overall tracking performance: the variance of the force trajectory (VarF(TOT)), as computed over sets of unperturbed trials, declined by 60% after the first 100 trials, but there was little additional improvement after the second 100 trials. Variance in the force finger space related to the total moment with respect to the pivot also showed a decline during the first half of practice and minimal further changes during the second half. In contrast, finger force variance that did not affect either total force or total moment showed no changes after the first 100 trials and a decline during the second 100 trials. This variance component quantified per finger was significantly larger than those related to the total force and total moment. The mean size of the TMS-induced phasic force increment decreased by 12% over the course of the 200 trials. The forces evoked in the index and ring fingers gradually became more equal, reducing the total moment with respect to the pivot and improving balance. We speculate that development of a relatively low twitch force with low total moment on the pivot made it easier for subjects to continue tracking after the TMS pulse. Such changes could well be correlated with the degree of corticospinal involvement in the task. The results suggest task specific, practice-related plastic changes in neural structures involved in the responses to TMS.

Adult↗

PubMed1999

Multiple synapse formation in the motor cortex opposite unilateral sensorimotor cortex lesions in adult rats.

Unilateral damage to the forelimb region of the sensorimotor cortex (FLsmc) in adult rats has previously been found to result in dendritic growth and synaptogenesis in layer V of the contralateral motor cortex. The neuronal growth appears to be mediated in part by lesion-induced changes in the use of the forelimbs. Whether these neuronal changes involve alterations in the structure and/or configuration of synaptic connections in layer V has not previously been investigated. The present study used stereological measures to characterize structural alterations in axonal processes and synaptic connections using electron micrographs generated in a previous study of the motor cortex contralateral to FLsmc lesions. Of primary interest were synapses formed by multiple synaptic boutons (MSBs), which have recently been found to be a major component of experience-related neocortical plasticity, and synapses with perforated postsynaptic densities (PSDs), which are putatively associated with enhanced synaptic efficacy. In comparison with sham-operated rats, there was an increase in the proportion and ratio of synapses to neurons formed by MSBs and in synapses with perforated PSDs at 30 days after the lesions. Furthermore, perforated synapses formed by MSBs were markedly increased at 18 and 30 days after the lesion in comparison with sham-operated rats. Preceding these synaptic structural changes (at 10 days postlesion), myelinated axons were reduced in volume fraction and volume per neuron in comparison with sham-operated rats but returned to normal levels at subsequent time points. These results are consistent with a lesion-induced degeneration and subsequent sprouting of axons. Together, these data indicate that a major restructuring of synaptic connectivity occurs in the cortex opposite FLsmc lesions in adult animals. This lesion-induced restructuring may be guided by ongoing changes in the use of the forelimbs.

Animals↗

PubMed1999

Functional neuronavigation with magnetoencephalography: outcome in 50 patients with lesions around the motor cortex.

The authors conducted a study to evaluate the clinical outcome in 50 patients with lesions around the motor cortex who underwent surgery in which functional neuronavigation was performed. The sensorimotor cortex was identified in all patients with the use of magnetoencephalography (MEG). The MEG-source localizations were superimposed onto a three-dimensional magnetic resonance image, and the image data set was then implemented into a neuronavigation system. Based on this setup, the surgeon chose the best surgical strategy. During surgery, the pre- and postcentral gyrus were identified by neuronavigation, and in addition, the central sulcus was localized using intraoperative recording of somatosensory evoked potentials. In all cases MEG localizations of the sensory or motor cortex were correct. In 30% of the patients preoperative paresis improved, in 66% no additional deficits occurred, and in only 4% (two patients) deterioration of neurological function occurred. In one of these patients the deterioration was not related to the method. The method of incorporating functional data into neuronavigation systems is a promising tool that can be used in more radical surgery to cause less morbidity around eloquent brain areas.

Journal Article↗

PubMed1989

[Transcranial magnetic stimulation of the motor cortex and percutaneous magnetic stimulation of the peripheral nervous structures in the dog].

The motor cortex was transcranially and peripheral nervous structures (motor roots, plexus, peripheral nerves) were percutaneously stimulated by magnetic pulses in awake dogs and in dogs awaking from general anesthesia. The compound muscle action potentials were recorded by surface or needle electrodes. The central motor conduction time as an information about central motor tracts was obtained by subtracting the peripheral latency from the corticomuscular latency. The peripheral latency was assessed by high voltage electrical and magnetic stimulation of motor roots and by the F-wave technique. The motor conduction velocity of the tibial nerve was measured by percutaneous magnetic and by electrical stimulation and the resulting values were compared.

Action Potentials↗

PubMed2002

Peri-ventricular grey stimulation versus motor cortex stimulation for post stroke neuropathic pain.

Central post stroke pain is often difficult to manage satisfactorily with conventional treatment modalities for pain. In the last decade functional neurosurgery has offered hope with motor cortex stimulation achieving significant alleviation of pain in some patients. Unfortunately this has led to the neglect of chronic stimulation of deep grey matter as another modality of treating this condition. In this article we present our experience with motor cortex stimulation and that with deep grey matter stimulation in patients with post stroke pain. We argue that both modalities have a significant role and that what is required are better methods of identifying particular patients who are more likely to respond to one or the other.

Aged↗