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PubMed2003

Modulation of motor cortex excitability by pallidal stimulation in patients with severe dystonia.

OBJECTIVE: To study the influence of continuous high-frequency electrical stimulation with electrodes implanted in the globus pallidus internus (GPi) on motor cortex excitability in nine patients with dystonia. METHODS: Short-term effects related to switching off and on the deep brain stimulator were investigated >3 months after electrode implantation. Activation of motor cortical excitatory and inhibitory neurons was examined with transcranial magnetic stimulation (TMS) by analysis of electromyographic activity in the hand muscles. Parameters of corticospinally mediated excitatory motor responses included latency, threshold, and response sizes with increasing stimulus intensities (stimulus-response curves). Other measures of motor cortex excitability comprised the duration of the contralateral silent period and intracortical inhibition and facilitation in a paired-pulse paradigm. RESULTS: Switching off GPi stimulation led to a decrease of motor cortex excitability, as reflected by an increase in motor thresholds (GPi stimulation on 37.5 +/- 6.1%, mean +/- SD; GPi stimulation off for 15 to 120 minutes, 40.5 +/- 6.7% of maximum stimulator output), and reduced the size of contralateral responses in the stimulus-response curves established for relaxed muscles. The changes were reversible within minutes after switching on GPi stimulation. They were associated with mild changes of dystonia. By contrast, measures of intracortical inhibition were not altered by switching off GPi stimulation. Spinal excitability did not change as assessed by H-reflex. CONCLUSION: GPi stimulation influences motor cortex excitability by a rapid modulation of thalamocortical outputs.

Adolescent↗
PubMed1995

Large-scale plasticity of the human motor cortex.

The adult primate brain is capable of modifying rapidly the size of cortical receptive fields or motor output modules in response to altered synaptic input. We used positron emission tomography (PET) to map the regional cerebral blood flow changes related to voluntary finger movements in patients with tumours occupying the hand area of motor cortex. All patients showed activations solely outside the tumour. Compared with the unaffected side, the activations were shifted by 9-43 mm either along the mediolateral body representation of motor cortex or into premotor or parietal somatosensory cortex. These results provide evidence that slowly developing lesions can induce large-scale reorganization that is not confined to changes within the somatotopic body representation in motor cortex.

Adult↗
PubMed1991

The intracortical position of pyramidal tract neurons in the motor cortex of the reeler changes from postnatal day 10 to adulthood.

To determine whether or not the intracortical distribution pattern of pyramidal tract (PT) neurons in the motor cortex (hindlimb area) of normal and reeler mutant mice changes during early postnatal development of the cortex, we injected HRP into the pyramidal decussation of postnatal day (P) 8 and adult animals of the normal and reeler strains, and killed the animals 2 days later. In the normal P10 and adult mice, such an injection resulted in a band of labelled neurons confined to the layer of large pyramids (LP), suggesting that the intracortical localization of PT neurons does not change from P10 to adulthood in the normal strain. In the P10 and adult reeler mice, labelled PT neurons were scattered radially from the deepest zone to the superficial zone of the motor cortex. However, while the HRP-labelled PT neurons are located bilaminarly in both the deepest zone and the superficial zone of the motor cortex of the P10 reeler mouse, the majority of PT neurons were found in the upper third of the motor cortex of the adult reeler mouse. Thus, the intracortical distribution pattern of PT neurons of the reeler mouse changes during the postnatal period.

Animals↗
PubMed1990

Dynamic organization of primary motor cortex output to target muscles in adult rats. II. Rapid reorganization following motor nerve lesions.

In the accompanying paper (Sanes et al. 1989), we demonstrated that the map of motor cortex (MI) output was reorganized when examined 1 week to 4 months after a motor nerve lesion in adult rats. The present experiments measured the extent of functional reorganization that occurs within the first hours after this lesion. Shifts in MI output were examined by testing the effect of stimulation at a site in MI vibrissa area before and up to 10 h after nerve section of the branches of the facial nerve that innervate the vibrissa. Immediately following nerve transection, no movement or forelimb EMG activity was evoked by intracortical electrical stimulation within the vibrissa area. Within hours of the nerve transection, however, stimulation elicited forelimb EMG responses that were comparable to those obtained by stimulating within the pre-transection forelimb area. Remapping of MI after nerve transection indicated that the forelimb boundary had shifted about 1 mm medially from its original location into the former vibrissa territory. Forelimb EMG could be evoked for up to 10 h within this reorganized cortex. These results indicated that the output circuits of MI can be quickly reorganized by nerve lesions in adult mammals.

Animals↗
PubMed1976

[Transcallosal modulation of a focus of maximal activity in the motor cortex].

In cats, EPs from 170 symmetrical points of the motor cortex were recorded during bilateral and unilateral stimulation of nerves of hind--and forelimbs. Charts of localization of the maximal activity foce (MAF) were drawn. Transection of the corpus callosum was shown to be followed by narrowing of MAFs during bilateral stimulation and by their enlargement during unilateral stimulation. The effect of MAF enlargement was found to be due to summation of thalamocortical and transcallosal projections in animals with intact callosal system, while the MAF narrowing effect--to be determined by reciprocal transcallosal influences. Existence of the spatial transcallosal modulation of thalamocortical projection in the motor cortex is supposed.

Animals↗
PubMed1992

Magnetic stimulation of motor cortex in relation to fastest voluntary motor activity in neurologically asymptomatic HIV-positive patients.

Forty-two HIV-positive patients of various CDC stages without clinically evident neurological deficits were examined with transcranial magnetoelectrical stimulation (TMS). Cortical as well as cervical and lumbar root stimulation was performed after excluding peripheral neuropathies in comparison to an age- and sex-matched control group. Whereas central conduction times were normal, conduction between cervical or lumbar roots and muscle was prolonged. Results were correlated to those of a motor test battery, which revealed slowing of fast alternating movements similar to findings in extrapyramidal disorders. Data indicate that proximal parts of the peripheral nervous system and extrapyramidal structures are subclinically involved in early HIV infection whereas the fastest corticospinal projections remain intact.

Adult↗
PubMed1998

"Threshold-level" multipulse transcranial electrical stimulation of motor cortex for intraoperative monitoring of spinal motor tracts: description of method and comparison to somatosensory evoked potential monitoring.

UNLABELLED: Numerous methods have been pursued to evaluate function in central motor pathways during surgery in the anesthetized patient. At this time, no standard has emerged, possibly because each of the methods described to date requires some degree of compromise and/or lacks sensitivity. OBJECT: The goal of this study was to develop and evaluate a protocol for intraoperative monitoring of spinal motor conduction that: 1) is safe; 2) is sensitive and specific to motor pathways; 3) provides immediate feedback; 4) is compatible with anesthesia requirements; 5) allows monitoring of spontaneous and/or nerve root stimulus-evoked electromyography; 6) requires little or no involvement of the surgical team; and 7) requires limited equipment beyond that routinely used for somatosensory evoked potential (SSEP) monitoring. Using a multipulse electrical stimulator designed for transcranial applications, the authors have developed a protocol that they term "threshold-level" multipulse transcranial electrical stimulation (TES). METHODS: Patients considered at high risk for postoperative deficit were studied. After anesthesia had been induced and the patient positioned, but prior to incision, "baseline" measures of SSEPs were obtained as well as the minimum (that is, threshold-level) TES voltage needed to evoke a motor response from each of the muscles being monitored. A brief, high-frequency pulse train (three pulses; 2-msec interpulse interval) was used for TES in all cases. Data (latency and amplitude for SSEP; threshold voltage for TES) were collected at different times throughout the surgical procedure. Postoperative neurological status, as judged by evaluation of sensory and motor status, was compared with intraoperative SSEP and TES findings for determination of the sensitivity and specificity of each electrophysiological monitoring technique. Of the 34 patients enrolled, 32 demonstrated TES-evoked responses in muscles innervated at levels caudal to the lesion when examined after anesthesia induction and positioning but prior to incision (that is, baseline). In contrast, baseline SSEPs could be resolved in only 25 of the 34 patients. During surgery, significant changes in SSEP waveforms were noted in 12 of these 25 patients, and 10 patients demonstrated changes in TES thresholds. Fifteen patients experienced varying degrees and durations of postoperative neurological deficit. Intraoperative changes in TES thresholds accurately predicted each instance of postoperative motor weakness without error, but failed to predict four instances of postoperative sensory deficit. Intraoperative SSEP monitoring was not 100% accurate in predicting postoperative sensory status and failed to predict five instances of postoperative motor deficit. As a result of intraoperative TES findings, the surgical plan was altered or otherwise influenced in six patients (roughly 15% of the sample population), possibly limiting the extent of postoperative motor deficit experienced by these patients. CONCLUSIONS: This novel method for intraoperative monitoring of spinal motor conduction appears to meet all of the goals outlined above. Although the risk of postoperative motor deficit is relatively low for the majority of spine surgeries (for example, a simple disc), high-risk procedures, such as tumor resection, correction of vascular abnormalities, and correction of major deformities, should benefit from the virtually immediate and accurate knowledge of spinal motor conduction provided by this new monitoring approach.

Adolescent↗
PubMed2006

Differences between the effects of three plasticity inducing protocols on the organization of the human motor cortex.

Several experimental protocols induce lasting changes in the excitability of motor cortex. Some involve direct cortical stimulation, others activate the somatosensory system and some combine motor and sensory stimulation. The effects usually are measured as changes in amplitude of the motor-evoked-potential (MEP) or short-interval intracortical inhibition (SICI) elicited by a single or paired pulses of transcranial magnetic stimulation (TMS). Recent work has also tested sensorimotor organization within the motor cortex by recording MEPs and SICI during short periods of vibration applied to single intrinsic hand muscles. Here sensorimotor organization is focal: MEPs increase and SICI decreases in the vibrated muscle, whilst the opposite occurs in neighbouring muscles. In six volunteers we compared the after effects of three protocols that lead to lasting changes in cortical excitability: (i) paired associative stimulation (PAS) between a TMS pulse and an electrical stimulus to the median nerve; (ii) motor practice of rapid thumb abduction; and (iii) sensory input produced by semicontinuous muscle vibration, on MEPs and SICI at rest and on the sensorimotor organization. PAS increased MEP amplitudes, whereas vibration changed sensorimotor organization. Motor practice had a dual effect and increased MEPs as well as affecting sensorimotor organization. The implication is that different protocols target different sets of cortical circuits. We speculate that protocols that involve repeated activation of motor cortical output lead to lasting changes in efficacy of synaptic connections in output circuits, whereas protocols that emphasize sensory inputs affect the strength of sensory inputs to motor circuits.

Adult↗
PubMedDate not supplied

[A computer model of generation of the motor cortex neuron processes seen in the course of execution of instrumental movement].

A computer model of neuronal processes in the motor cortex column is presented. The model is consisted of two pyramidal cell layers with two groups of inhibitory interneurons, selectively controlling pyramidal cell soma and dendrite, in each. Active Na, Ca and K conductances are included in the model of a single neuron. Horizontal excitatory connections between pyramidal cells in the upper layer are largely of NMDA-receptor type, that in the lower layer--of non-NMDA-type. All inhibitory synapses are of GABA(A)-type. The model reproduces the main phenomenon observed in the motor cortex during the execution of conditioned movements. Consequent to an early excitation the upper layer pyramidal cells generate a late NMDA-dependent reflexive response to afferent conditional stimulation, which as in a real case is diminished by GABA(A)-type synaptic inhibition and afferent stimulus strength increase. The characteristic inverse relation between the late response manifestation and the stimulus strength observed in the real cortex can be reproduced in the model only if NMDA-glutamate receptors were preferentially localized in the terminals of pyramidal cell backward collaterals, not in the terminals of the afferent fibers on pyramidal neurons. The intended component of motor cortex neuronal activity is generated in NMDA-independent manner by the pyramidal cells of lower layer. The slow time coarse of intended component as compared with short duration of AMPA epsp's is due to a consecutive relay-race--like activation of pyramidal neurons with different dendrit-to-soma ratio.

Animals↗
PubMed2001

Somatotopy of the motor cortex after long-term spinal cord injury or amputation.

Certain brain-computer interface (BCI) methods use intrinsic signals from the motor cortex to control neuroprosthetic devices. The organization of the motor pathways in those populations likely to use neuroprosthetic devices, therefore, needs to be determined; there is evidence that following disease or injury the representation of the body in the motor cortex may change. In this study, functional MRI measures of somatotopy following spinal cord injury (SCI) showed evidence of changes in limb representations in the motor cortex. Subjects with chronic SCI had unusual cortical patterns of activity when attempting to move limbs below their injury; amputees showed a more normal somatotopy. The functional reorganization may affect optimal implanted electrode placements for invasive BCI methods for these different populations.

Adult↗
PubMed1989

[Percutaneous electric and magnetic stimulation of the motor cortex in man. Physiological aspects and clinical applications].

The new techniques of percutaneous electric and magnetic stimulation of the motor cortex in conscious man provide a unique opportunity of functional testing of the central motor pathways. These techniques seem to be safe and no immediate or delayed adverse reactions have been reported. The physiological studies so far performed suggest that the structures which are preferentially excited by these methods are the fast conducting pyramidal neurones. It has been shown that a single cortical stimulus is able to activate spinal motoneurones repeatedly. This phenomenon can easily be explained if the cortical stimulus generates multiple descending volleys in the central motor pathways. By comparison with experiments of stimulation of the exposed motor cortex in animals, it is likely that electric brain stimulation directly activates the axons of the pyramidal neurons at their origin and to a lesser extent also recruits these neurons transsynaptically, via some cortical interneurones. Magnetic stimulation of the brain at the vertex seems to act mostly by the latter mechanism. These different modes of action of the two methods of cortical stimulation explain the latency differences of the EMG responses obtained with either technique. Increased excitability of the spinal motoneurones and the existence of multiple descending volleys in response to a single cortical stimulus result in shortening of the latencies and greater amplitude of the responses recorded during voluntary contraction of the target muscle. Stimulation of the motor cortex has been used in pilot studies conducted on patients suffering from various disorders of the central motor pathways, such as multiple sclerosis, cervical spondylosis, motor neurone disease or stroke. The sensitivity of the technique looks promising. In M.S., the EMG responses usually show an increased central conduction latency, a reduced amplitude and a prolonged duration. The severity of the electrophysiological abnormalities is not very well correlated with clinical weakness, but the correlations seems to be better with hyperreflexia and the presence of brisk finger flexor jerks. The same abnormalities are observed in cervical spondylosis, although to a lesser extent. In motor neurone disease, the responses have a moderately increased latency and their size and duration are markedly reduced. Patients with acute hemispheric stroke usually show absent responses on the contralateral side. Finally, electric cortical stimulation can be very useful in monitoring the functional integrity of descending motor tracts during surgical operations performed on the spinal cord.

Central Nervous System Diseases↗
PubMed2007

Amygdala interconnections with the cingulate motor cortex in the rhesus monkey.

Amygdala interconnections with the cingulate motor cortices were investigated in the rhesus monkey. Using multiple tracing approaches, we found a robust projection from the lateral basal nucleus of the amygdala to Layers II, IIIa, and V of the rostral cingulate motor cortex (M3). A smaller source of amygdala input arose from the accessory basal, cortical, and lateral nuclei, which targeted only the rostral region of M3. We also found a light projection from the lateral basal nucleus to the same layers of the caudal cingulate motor cortex (M4). Experiments examining this projection to cingulate somatotopy using combined neural tracing strategies and stereology to estimate the total number of terminal-like immunoreactive particles demonstrated that the amygdala projection terminates heavily in the face representation of M3 and moderately in its arm representation. Fewer terminal profiles were found in the leg representation of M3 and the face, arm, and leg representations of M4. Anterograde tracers placed directly into M3 and M4 revealed the amygdala connection to be reciprocal and documented corticofugal projections to the facial nucleus, surrounding pontine reticular formation, and spinal cord. Clinically, such pathways would be in a position to contribute to mediating movements in the face, neck, and upper extremity accompanying medial temporal lobe seizures that have historically characterized this syndrome. Alterations within or disruption of the amygdalo-cingulate projection to the rostral part of M3 may also have an adverse effect on facial expression in patients presenting with neurological or neuropsychiatric abnormalities of medial temporal lobe involvement. Finally, the prominent amygdala projection to the face region of M3 may significantly influence the outcome of higher-order facial expressions associated with social communication and emotional constructs such as fear, anger, happiness, and sadness.

Amino Acids↗
PubMed1993

Motor cortex stimulation measured by magnetic resonance imaging on a standard 1.5 T clinical scanner.

The authors report the effects of motor cortex stimulation of normal volunteers using conventional MR imaging techniques on a standard 1.5 T clinical scanner. A circular polarized head coil has been used normally for the stimulation measurements, although improvement in signal-to-noise 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 0.2 ppm. The imaging technique used was a conventional two-dimensional, first order flow rephased, gradient echo FLASH sequence with TR = 73 msec, TE = 60 msec, flip angle = 40 degrees. The stimulation experiments measured with the head coil were performed with a 64 x 128 matrix size, at a FOV = 230 mm, with NEX = 2 and 10 mm slice thickness. In case of stimulation measurements using the surface coil a 128 x 128 matrix size, a FOV = 200 mm, with NEX = 1 and a 5 mm slice thickness have been used. Total single scan time for one slice was 12 sec in both cases. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. An increase in signal of order 4% in the motor cortex for the head coil measurements was observed, whereas of order 10% signal increase was detected for the surface coil measurements with smaller voxel size. The reported data demonstrate the technical feasibility of functional MR imaging using conventional sequences and equipment.

Feasibility Studies↗
PubMed2002

Functional reorganization of motor cortex increases with greater axonal injury from CADASIL.

BACKGROUND AND PURPOSE: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited small-artery disease that clinically involves only the brain. Particularly early in the disease, patients can show substantial or complete recovery after individual strokes. Cortical functional reorganization may contribute to limiting disability with such ischemic injury. We sought to test whether the extent of any functional changes in the motor cortex increases with greater brain axonal injury from CADASIL. METHODS: Functional MRI (fMRI) was used to characterize cortical activation during a simple hand-tapping task. Disease-associated pathology in subcortical white matter was assessed with the use of conventional fluid-attenuated inversion recovery (FLAIR) MRI and MR spectroscopic imaging for measurement of N-acetyl aspartate decreases, a relatively specific measure of axonal injury. RESULTS: There was evidence for variable but substantial hyperintense white matter signal in all of the patients with FLAIR imaging. With the use of fMRI, the brain regions activated during motor tasks were similar for the 9 CADASIL patients and 7 controls, except that most (6 of 9) patients showed primary motor cortex activation both ipsilateral and contralateral to the hand moved, a finding in only 1 of 7 healthy controls. Ipsilateral motor cortex activation increased (r=-0.77, P<0.05) and motor cortex activation lateralization index decreased (r=0.68, P<0.02) with greater white matter injury (as assessed from decreases in the relative N-acetyl aspartate concentration) in a region of interest including descending motor fibers of the corticospinal pathway. CONCLUSIONS: The extent of functional reorganization of motor cortex increases with increasing axonal injury, consistent with an adaptive role for these changes. Increased functional recruitment of cortex ipsilateral to the limb moved therefore may contribute to limiting motor impairment from the subcortical injury of CADASIL.

Adaptation, Physiological↗
PubMed2005

Comparison of functional MR imaging guidance to electrical cortical mapping for targeting selective motor cortex areas in neuropathic pain: a study based on intraoperative stereotactic navigation.

PURPOSE: To assess the concordance between data from functional MR imaging (fMRI) guidance and the intraoperative electrical cortical mapping (iCM) in targeting selective motor cortex areas in refractory neuropathic pain. METHODS: Twenty-one patients (11 women and 10 men; mean age, 55.6 years) with refractory central (ischemic, 8 cases) and neuropathic pain (trigeminal neuropathy, 6 cases; syrinx/amputation/plexus trauma, 7 cases) underwent surgery for the implantation of an epidural electrode for chronic motor cortex stimulation (MCS) with general anesthesia and a frameless neuronavigation system used for the image-guided targeting procedure. All patients were studied by preoperative fMRI and epidural iCM with somatosensory evoked potentials and motor cortex stimulodetection. fMRI investigated systematically motor tasks of both hands and that related to the somatic area (foot or tongue) affected by pain. fMRI data were analyzed with the Statistical Parametric Mapping99 software (initial analysis threshold [AT] corresponding to P < .001), registered in the neuronavigation system and correlated intraoperatively with iCM. Matching of fMRI and iCM was specifically examined, focusing the study on hand mapping. RESULTS: Concordance between contours of fMRI activation area and iCM in precentral gyrus (mean distance, 3.8 mm) was found in 20/21 patients (95%). Because precision of iCM was suboptimal in 7 patients, concordance for more restrictive values of the AT (P < .0001) was found in only 13 of these 20 patients. Concordance was not found in one patient, as result of image distortion and residual motion artifact. CONCLUSIONS: In this study, fMRI guidance provides information that matches those of an independent functional method. These data illustrate the functional accuracy of fMRI guidance for the operative targeting of selective motor cortex areas in neuropathic pain.

Adult↗