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At least 19 recordsLinked to original sources
PubMed2002

Induction of persistent changes in the organisation of the human motor cortex.

Motor learning must involve changes in the organisation of the brain, and it seems axiomatic that afferent signals generated during repeated motor practice contribute to this. In this study, motor-point stimulation of the first dorsal interosseous (FDI) muscle was paired with transcranial magnetic stimulation of the human motor cortex on three successive days to determine whether repeated stimulation sessions result in enduring reorganisation of the motor cortex. This repeated "dual" stimulation induced significant changes in the excitability of the motor cortex together with expansion of the area of scalp from which these responses were elicited. The expansion in muscle representation was accompanied by large movements in the centre of gravity (CoG), suggesting a true reorganisation of the underlying cortical representational zone. The changes persisted for at least 2 days following the last stimulation session. It is concluded that repeated dual stimulation is capable of inducing long-lasting reorganisation within the motor cortex. These changes may be similar in nature to those seen in the motor cortex during motor learning. Moreover, these observations suggest that it may be possible to induce the motor cortex of patients who have suffered strokes to reorganise in a way that improves the voluntary control of the weakened muscles.

Adult↗
PubMed2002

Organization of ipsilateral excitatory and inhibitory pathways in the human motor cortex.

Motor cortex stimulation has both excitatory and inhibitory effects on ipsilateral muscles. Excitatory effects can be assessed by ipsilateral motor-evoked potentials (iMEPs). Inhibitory effects include an interruption of ipsilateral voluntary muscle activity known as the silent period (iSP) and a reduction in corticospinal excitability evoked by conditioning stimulation of the contralateral motor cortex (interhemispheric inhibition, IHI). Both iSP and IHI may be mediated by transcallosal pathways. Their relationship to the contralateral corticospinal projection and whether iSP and IHI represent the same phenomenon remain unclear. The neuronal population activated by transcranial magnetic stimulation (TMS) is highly dependent on the direction of the induced current in the brain. We examined the relationship among iMEP, iSP, IHI, and the contralateral corticospinal system by examining the effects of different stimulus intensities and current directions. Surface electromyography (EMG) was recorded from both first dorsal interosseous (FDI) muscles. The iSP in the right FDI muscle was obtained by right motor cortex stimulation during voluntary muscle contraction. IHI was examined by conditioning stimulation of the right motor cortex followed by test stimulation of the left motor cortex at interstimulus intervals (ISIs) of 2-80 ms. The induced current directions tested in the right motor cortex were anterior medial (AM), posterior medial (PM), posterior lateral, and anterior lateral (AL). Contralateral MEPs (cMEPs) had the lowest threshold with the AM direction and the shortest latency with the PM direction. iMEPs were present in 8 of 10 subjects. Both iMEP and IHI did not show significant directional preference. iSP was observed in all subjects with the highest threshold for the AL direction and the longest duration for the AM direction. cMEP, iSP, and IHI all increased with stimulus intensity up to approximately 75% stimulator output. Target muscle activation decreased IHI at 8-ms ISI but had little effect on IHI at 40-ms ISI. iSP and IHI at 8-ms ISI did not correlate at any stimulus intensities and current directions tested, and factor analysis showed that they are explained by different factors. However, active IHI at 40-ms ISI was explained by the same factor as iSP. The different directional preference for cMEP compared with iMEP and IHI suggests that these ipsilateral effects are mediated by populations of cortical neurons that are different from those activating the corticospinal neurons. iSP and IHI do not represent the same phenomenon and should be considered complementary measures of ipsilateral inhibition.

Adult↗
PubMed2004

Consolidation of dynamic motor learning is not disrupted by rTMS of primary motor cortex.

Motor skills, once learned, are often retained over a long period of time. However, such learning first undergoes a period of consolidation after practice. During this time, the motor memory is susceptible to being disrupted by the performance of another motor-learning task. Recently, it was shown that repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex could disrupt the retention of a newly learned ballistic task in which subjects had to oppose their index finger and thumb as rapidly as possible. Here we investigate whether the motor cortex is similarly involved during the consolidation that follows learning novel dynamics. We applied rTMS to primary motor cortex shortly after subjects had either learned to compensate for a dynamic force field applied to their index finger or learned a ballistic finger abduction task. rTMS severely degraded the retention of the learning for the ballistic task but had no effect on retention of the dynamic force-field learning. This suggests that, unlike learning of simple ballistic skills, learning of dynamics may be stored in a more distributed manner, possibly outside the primary motor cortex.

Adult↗
PubMed2006

The organization of behavioral repertoire in motor cortex.

Motor cortex in the primate brain was once thought to contain a simple map of the body's muscles. Recent evidence suggests, however, that it operates at a radically more complex level, coordinating behaviorally useful actions. Specific subregions of motor cortex may emphasize different ethologically relevant categories of behavior, such as interactions between the hand and the mouth, reaching motions, or defensive maneuvers to protect the body surface from impending impact. Single neurons in motor cortex may contribute to these behaviors by means of their broad tuning to idiosyncratic, multijoint actions. The mapping from cortex to muscles is not fixed, as was once thought, but instead is fluid, changing continuously on the basis of feedback in a manner that could support the control of higher-order movement parameters. These findings suggest that the motor cortex participates directly in organizing and controlling the animal's behavioral repertoire.

Animals↗
PubMed2001

Modulation of practice-dependent plasticity in human motor cortex.

Motor practice may lead to expansion of trained representations in the motor cortex, but it is unknown whether this practice-dependent plasticity can be purposefully enhanced or depressed. Evidence, mainly based on animal experiments, indicates that the activity of GABA-related cortical inhibition is important in controlling the extent to which plasticity may occur. We tested the role of GABA in modulating practice-dependent plasticity in the human motor cortex. A decrease in GABA-related cortical inhibition was achieved by ischaemic nerve block (INB) in the hand by deafferentation/deefferentation and an increase was achieved by administration of the GABA(A) receptor agonist lorazepam. In Experiment 1, healthy subjects performed motor practice (MP), consisting of repeated ballistic contractions of the biceps muscle in the absence (MP alone) or presence of INB (MP+INB). Changes in the biceps motor cortex representation were assessed by transcranial magnetic stimulation (TMS). MP+INB resulted in a dramatic increase in the size of the motor evoked potential (MEP) and in paired-pulse excitability compared with mild or no changes in the MP-alone and INB-alone conditions. In Experiment 2, this dramatic increase in biceps representation induced by MP+INB was replicated when subjects were pretreated with placebo, but this increase was prevented or even switched to a decrease when subjects were pretreated with lorazepam. These findings indicate that a decrease in GABA-related inhibition facilitates practice-dependent plasticity in the human motor cortex, whereas an increase depresses it. In Experiment 3, practice-dependent plasticity (assessed by TMS, as in the first two experiments) was also tested at the behavioural level. The dramatic increase in biceps MEP size induced by MP+INB was paralleled by an increase in peak acceleration of the fastest elbow flexion movements. Similarly, the lack of change in MEP size in the MP-alone condition was paralleled by a lack of change in peak acceleration. We propose that changes in GABA activity may be instrumented to modulate plasticity purposefully; for instance, to enhance plastic change and recovery of function after a lesion in neurological patients.

Adult↗
PubMed1995

Cortical stimulation for central neuropathic pain: 3-D surface MRI for easy determination of the motor cortex.

Motor cortex electric stimulation has been reported to be effective for the treatment of central post-stroke pain and trigeminal neuropathic pain. Five patients with pain due to injury of the trigeminal nerve and with abnormalities of facial sensibility, as well as two patients suffering of a post-stroke thalamic pain, were subjected to stimulation applied epidurally on the motor cortex. Quadripolar electrodes were implanted under local anaesthesia and the precise location of the motor cortex was determined on three-dimensional surface MRI the day prior to surgery. In our experience, correct topographic localization of the electrode on the motor cortex seems to be crucial to obtain pain reduction.

Adult↗
PubMed2006

BDNF val66met polymorphism is associated with modified experience-dependent plasticity in human motor cortex.

Motor training can induce profound physiological plasticity within primary motor cortex, including changes in corticospinal output and motor map topography. Using transcranial magnetic stimulation, we show that training-dependent increases in the amplitude of motor-evoked potentials and motor map reorganization are reduced in healthy subjects with a val66met polymorphism in the brain-derived neurotrophic factor gene (BDNF), as compared to subjects without the polymorphism. The results suggest that BDNF is involved in mediating experience-dependent plasticity of human motor cortex.

Adult↗
PubMed2005

Spinal dorsal horn neuron response to mechanical stimuli is decreased by electrical stimulation of the primary motor cortex.

Motor cortex stimulation (MCS) has been used clinically as a tool for the control for central post-stroke pain and neuropathic facial pain. The underlying mechanisms involved in the antinociceptive effect of MCS are not clearly understood. We hypothesize that the antinociceptive effect is through the modulation of the spinal dorsal horn neuron activity. Thirty-two wide dynamic range spinal dorsal horn neurons were recorded, in response to graded mechanical stimulation (brush, pressure, and pinch) at their respective receptive fields, while a stepwise electrical stimulation was applied simultaneously in the motor cortex. The responses to brush at control, 10 V, 20 V, and 30 V, and recovery were 11.5+/-1.6, 12.1+/-2.6, 11.1+/-2.2, 10.5+/-2.1, and 13.2+/-2.5 spikes/s, respectively. The responses to pressure at control, 10 V, 20 V, and 30 V, and recovery were 33.2+/-6.1, 22.9+/-5.3, 20.5+/-5.0, 17.3+/-3.8, and 27.0+/-4.0 spikes/s, respectively. The responses to pinch at control, 10 V, 20 V, and 30 V, and recovery were 37.2+/-6.4, 26.3+/-4.7, 25.9+/-4.7, 22.5+/-4.3, and 35.0+/-6.2 spikes/s, respectively. It is concluded that, in the rat, electrical stimulation of the motor cortex produces significant transient inhibition of the responses of spinal cord dorsal horn neurons to higher intensity mechanical stimuli without affecting their response to an innocuous stimulus.

Action Potentials↗
PubMed1991

Magnetic stimulation of motor cortex and motor roots for painless evaluation of central and proximal peripheral motor pathways. Normal values and clinical application in disorders of the lumbar spine.

Magnetic stimulation of the motor cortex, motor roots, and proximal nerve trunks was performed in 46 healthy adults and in 73 consecutive patients with disorders of the lumbar spine. In combination with neurography and F-wave recordings, the fractionated stimulation of the motor pathways allowed calculation of conduction times of the pyramidal tract fibers, of the motor roots (ie, caudal fibers), and of the motor fibers of the lumbosacral plexus. Normal values for motor conduction times to the quadriceps, anterior tibial, and extensor digitorum brevis muscles were established. Patients had clinical and radiologic diagnoses of spinal stenosis (n = 43) and nerve root compression syndromes (n = 30). Motor conduction times to lower limb muscles were significantly delayed (above mean normal value +/- 2 x SD) in 65% of the patients with spinal stenosis and 50% of the patients with nerve root compression syndromes. Conduction slowing could be localized within the motor root and caudal fiber segment of the motor pathways in 80% of the patients in whom F-waves could be recorded. This method can be used to verify, quantify, and locate lesions of the motor pathways in conditions such as compression of the spinal cord, the caudal fibers (spinal stenosis), or the motor root passing through the intervertebral canal.

Adult↗
PubMed1985

Modification of the projection from the sensory cortex to the motor cortex following the elimination of thalamic projections to the motor cortex in cats.

Examination of the projection from area 2 of the sensory cortex to the motor cortex revealed substantial changes following lesion of the ventrolateral nucleus of the thalamus. These observed changes were as follows. (1) The polarity of the evoked potentials elicited by area 2 stimulation reversed in the depth of the motor cortex whereas in normal animals, there was no reversal. (2) The amplitude of area 2-elicited EPSPs in the motor cortical neurons became greater following the lesion of VL. (3) The shape of the observed EPSPs was characterized by multiple peaks whereas in normal animals, the EPSPs were generally smooth and monophasic. (4) Neurons receiving a short-latency input from area 2 were distributed throughout the depths of the motor cortex whereas in normal animals, they were located only in the upper layers (layers II and III). (5) Intracellular injection of HRP revealed that the neurons receiving short-latency input were not restricted to typical stellate type cells, but also included bipolar or bitufted neurons with elongated cell bodies and polarized arborizations. These neurons were located in the superficial (II and III) as well as in the deep (V) layer. It is concluded that the elimination of thalamic input resulted in the reinforcement of the corticocortical input to the motor cortex. The subsequently observed corticocortical projection extended to neurons did not originally innervated by the association fibers. The results suggested that functional recovery following thalamic lesion is partly due to reorganization of projections from the sensory cortex to the motor cortex.

Animals↗
PubMed1998

Functional reorganization of the rat motor cortex following motor skill learning.

Functional reorganization of the rat motor cortex following motor skill learning. J. Neurophysiol. 80: 3321-3325, 1998. Adult rats were allocated to either a skilled or unskilled reaching condition (SRC and URC, respectively). SRC animals were trained for 10 days on a skilled reaching task while URC animals were trained on a simple bar pressing task. After training, microelectrode stimulation was used to derive high resolution maps of the forelimb and hindlimb representations within the motor cortex. In comparison with URC animals, SRC animals exhibited a significant increase in mean area of the wrist and digit representations but a decrease in elbow/shoulder representation within the caudal forelimb area. No between-group differences in areal representation were found in either the hindlimb or rostral forelimb areas. These results demonstrate that motor skill learning is associated with a reorganization of movement representations within the rodent motor cortex.

Animals↗
PubMed1991

The striatum and motor cortex in motor initiation and execution.

The participation of striatal and motor cortex neurons in motor initiation and execution was studied using single neuronal recording in 3 monkeys performing wrist flexion and extension stimulus-initiated reaction time tasks. Observations of 46 striatal neurons whose activity correlated with the tasks were compared to recordings of 59 task-related motor cortex neurons. Neurons were classified as best related to the appearance of the go signal, movement onset, agonist or antagonist electromyographic changes, or the movement reaching target. Timing of neuronal activity changes in both striatum and motor cortex suggested that go signal-related neurons represent input function while most movement onset-related neurons represent output function. In the striatum, those related to reaching target represent output function. Furthermore, go signal-related neurons usually change activity before movement onset-related neurons which change activity prior to target attainment-related neurons. These observations suggest a hierarchical organization within the striatum and motor cortex. Also the striatum participates in programming target acquisition as well as motor initiation.

Animals↗
PubMed2000

Laterality, somatotopy and reproducibility of the basal ganglia and motor cortex during motor tasks.

We investigated the basal ganglia, motor cortex area 4, and supplementary motor area (SMA) using functional magnetic resonance imaging (fMRI) and five motor tasks: switching between finger and toe movements, writing, finger tapping, pronation/supination, and saccadic eye movements. We found reliable activation in the caudate nucleus and putamen in single subjects without the need for inter-subject averaging. Percent signal changes in basal ganglia were smaller by a factor of three than those in SMA or motor cortex (1% vs. 2.5-3%). There was a definite foot-dorsal, hand-ventral basal ganglia somatotopy, similar to prior data from primates. Saccadic eye movements activated the caudate nucleus significantly more than the other tasks did. Unilateral movements produced bilateral activation in the striatum even when motor cortex activation was unilateral. Surprisingly, bilateral performance of the tasks led, on average, to consistently smaller basal ganglia activation than did unilateral performance (P<0.001), suggesting less inhibition of contralateral movements during bilateral tasks. Moreover, there was a striking dominance pattern in basal ganglia motor activation: the left basal ganglia were more active than the right for right handers, regardless of the hand used. This lateralization appears much stronger than that previously reported for motor cortex. Comparisons of inter-subject and intra-subject reproducibility indicated a much larger variability in basal ganglia and SMA compared to motor cortex, in spite of similar percent signal changes in the latter two structures.

Adult↗
PubMed1987

Reorganization of the projection from the sensory cortex to the motor cortex following elimination of the thalamic projection to the motor cortex in cats; Golgi, electron microscope and degeneration study.

Changes of terminal connections of projection fibers from area 2 of the sensory cortex to the motor cortex following chronic lesion in the thalamus were examined using the electron microscope. The lesioned areas included nucleus ventralis anterior, n. ventralis lateralis and rostral part of n. ventralis posterolateralis. The synaptic sites were identified using the Golgi impregnation method to identify postsynaptic neurons in the motor cortex and the axonal degeneration method to identify presynaptic terminals of fibers originating from area 2. The following results were obtained. (1) The number of degenerating terminals per unit area in the motor cortex was increased to nearly twice that in normal animals. (2) The number of degenerating terminals synapsing with stellate cells was not increased but stayed more or less the same as in normal animals. (3) The number of degenerating terminals contacting pyramidal cells increased substantially, to more than twice that in normal animals. (4) These newly formed synapses were found on proximal dendritic shafts of the pyramidal cells in both layers III and V, suggesting that these synapses occupied the spaces where the thalamocortical terminals were located. (5) The functional significance of these newly formed synapses was discussed in relation to the recovery of motor function following thalamic lesion.

Animals↗
PubMed2006

Decreased input to the motor cortex increases motor cortical excitability.

OBJECTIVE: To investigate whether a short-duration reduction of input to the motor cortex affects excitability in the hand region of the motor cortex. METHODS: Subjects (n=10) received sets of transcranial magnetic stimulation of the motor cortex (TMS) and peripheral ulnar nerve stimulation. Stimuli were delivered before and after 20 min of inactivity of the test hand. The evoked compound muscle action potentials were recorded in two relaxed intrinsic hand muscles using surface EMG. RESULTS: Motor evoked potential size (MEP; expressed relative to the maximal M-wave) increased by approximately 30-40 in both hand muscles (P=0.012) following inactivity. The enlarged MEP was not associated with changes in F-wave size, a marker of motoneurone excitability, or changes in intracortical inhibition and facilitation measured with paired-pulse TMS. CONCLUSIONS: MEP growth most likely reflects an increase in motor cortical excitability. The increased excitability appears to be more associated with reduced voluntary drive to and from the motor cortex rather than reduced afferent input from the periphery. SIGNIFICANCE: These results have important implications for any investigation of motor cortical excitability in relaxed subjects. The outcome of an experimental intervention is the net result of the intervention itself and alterations in cortical excitability produced by the subjects' inactivity.

Adult↗
PubMed1994

Reliability of transcranial magnetic stimulation for mapping the human motor cortex.

Motor mapping using transcranial magnetic stimulation has been applied to the study of adaptive and restorative mechanisms of the motor cortex. To date, the reproducibility of mapping techniques has yet to be investigated in detail and/or confirmed. We report a technique used to map the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) motor cortices of 6 normal volunteers, each studied on 2 occasions separated by several weeks (range of 21-132 days). APB and ADM results were analyzed separately, with area and volume characteristics subjected to analysis of variance. Coefficients of variation, which should be low, ranged from 14% to 37% and coefficients of reliability, which should be high, ranged from 63% to 94%, indicating that the described technique for motor mapping is responsible.

Adult↗
PubMed1994

N-methyl-D-aspartate (NMDA) receptors in the spinal cord and motor cortex in motor neuron disease: a quantitative autoradiographic study using [3H]MK-801.

The distribution and density of NMDA receptors in spinal cord and motor cortex was compared in motor neuron disease (MND; 10 cases) and controls (8 cases) using [3H]MK-801 autoradiography. In the spinal ventral horn of MND cases, [3H]MK-801 binding was reduced and there were fewer focal hot spots of binding. These changes are likely to reflect loss of motor neurons (MN) bearing NMDA receptors. [3H]MK-801 binding was increased in intermediate spinal grey matter and deeper layers of the motor cortex in MND cases compared to controls. This may represent either an adaptive response to MN loss or a pathophysiological phenomenon contributing to MN degeneration.

Aged↗
PubMed1997

Involvement of primary motor cortex in motor imagery: a neuromagnetic study.

Functional brain imaging studies have indicated that several cortical and subcortical areas active during actual motor performance are also active during imagination or mental rehearsal of movements. Recent evidence shows that the primary motor cortex may also be involved in motor imagery. Using whole-scalp magnetoencephalography, we monitored spontaneous and evoked activity of the somatomotor cortex after right median nerve stimuli in seven healthy right-handed subjects while they kinesthetically imagined or actually executed continuous finger movements. Manipulatory finger movements abolished the poststimulus 20-Hz activity of the motor cortex and markedly affected the somatosensory evoked response. Imagination of manipulatory finger movements attenuated the 20-Hz activity by 27% with respect to the rest level but had no effect on the somatosensory response. Slight constant stretching of the fingers suppressed the 20-Hz activity less than motor imagery. The smallest possible, kinesthetically just perceivable finger movements resulted in slightly stronger attenuation of 20-Hz activity than motor imagery did. The effects were observed in both hemispheres but predominantly contralateral to the performing hand. The attempt to execute manipulatory finger movements under experimentally induced ischemia causing paralysis of the hand also strongly suppressed 20-Hz activity but did not affect the somatosensory evoked response. The results indicate that the primary motor cortex is involved in motor imagery. Both imaginative and executive motor tasks appear to utilize the cortical circuitry generating the somatomotor 20-Hz signal.

Adult↗