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PubMed1978

Projection from area 3a to the motor cortex by neurons activated from group I muscle afferents.

Two receiving areas in the pericruciate cortex are known for inputs from group I muscle afferents of forelimb nerves. One focus is near the postcruciate dimple of area 3a, and the other in the lateral sigmoid gyrus of the motor cortex (area 4gamma). The cortico-cortical projection of area 3a to 4gamma, and the relay by this projection of group I muscle afferent input to the motor cortex were investigated in cats. The following results were obtained. 1. Seventy-four neurons within area 3a were antidromically activated by intracortical microstimulation of the motor cortex. 2. Although excitation evoked by stimulation of group I muscle afferents could be demonstrated for only a few (8 of 48) cortico-cortical neurons in extracellular recordings, due to the methodological limitations discussed, this input evoked EPSPs in 8 of 9 cortico-cortical neurons recorded intracellularly. Therefore, it is likely that the majority of neurons projecting from area 3a to the motor cortex have an excitatory synaptic input from group I afferents. 3. Neurons projecting from area 3a to the motor cortex were most commonly found in cortical layer III, although some were found in layer V. 4. Five of nine pyramidal tract neurons of area 3a had a strong excitatory synaptic input from group I muscle afferents. 5. A new type of pyramidal tract neuron was found which has cortico-cortical axon collaterals connecting the two cytoarchitectonic regions. These various neurons may be part of a feedback system from muscle afferents to the motor cortex.

Afferent Pathways↗

PubMed2006

Motor cortex excitability in stroke before and after constraint-induced movement therapy.

OBJECTIVE: To investigate motor cortex excitability in stroke patients and explore excitability changes induced by an intense physiotherapy. METHODS: We studied 12 chronic stroke patients (6 cortical, 6 subcortical lesions) before and after participation in 12 days of constraint-induced movement therapy. Transcranial magnetic stimulation was applied to test intracortical inhibition (ICI), intracortical facilitation, silent periods, amplitudes of motor evoked potentials, and motor thresholds. Motor function was assessed by the Motor Activity Log, the Wolf Motor Function Test, and the Modified Ashworth Scale for spasticity. RESULTS: Motor evoked potential amplitudes and motor thresholds were inversely correlated, indicating that both parameters reflect the function of corticospinal pathways. Before therapy, a motor cortex disinhibition was found in the affected hemisphere. This disinhibition was stronger in patients with cortical lesions. The amount of disinhibition was correlated with the degree of spasticity. After therapy, ICI changes were more pronounced in the affected hemisphere compared with the unaffected side. Both ICI decreases and increases were observed. Motor function tests indicated an improvement in all patients. CONCLUSIONS: Motor cortical disinhibition is present in chronic stroke patients. Therapy-associated changes of motor cortex excitability mainly occur in the lesioned hemisphere by up-regulation or down-regulation of ICI. We replicate that constraint-induced movement therapy improves motor functions in the chronic stage after stroke.

Adult↗

PubMed1992

Area 3a in the cat. II. Projections to the motor cortex and their relations to other corticocortical connections.

It is well known that area 3a in the cat may monosynaptically influence the activity of neurons in the motor cortex. Much less information is available, however, on the anatomy of these connections. By using single or combined injections of different retrograde axonal tracers, we investigated the topography (horizontal and laminar) of area 3a neurons projecting to the motor cortex, and the anatomical relationships between these neurons and those projecting to other areas (2, 5, and SII) which, in turn, project to the motor cortex. Area 3a projects to all parts of area 4 gamma, to area 4 delta, and to the agranular area 6 in the lateral bank of the presylvian sulcus (area 6 alpha gamma), but not to other parts of areas 4 and 6. This projection exhibits a loose topographic organization along the mediolateral dimension of area 3a, and, in many cases, arises predominantly from the rostral half of this area. Although single small injections in the motor cortex produced two or more separate patches of retrograde labeling in 3a, after simultaneous injections of fluorochromes in two separate loci there often appeared in area 3a overlapping populations of neurons which were labeled retrogradely by each of the dyes, but with very few double-labeled neurons. In horseradish peroxidase (HRP) cases, 72% of area 3a neurons projecting to area 4 gamma were distributed in supragranular layers (mainly layer III), although the proportion of labeling in infragranular layers was larger when using fluorescent dyes. Double-labeled cells predominated in infragranular layers. These results have a bearing upon the functional roles that have been attributed to area 3a, as a cortical locus involved in muscle sensation, and a cortical relay to the motor cortex of rapid feedback information from muscle activity during movement.

Amidines↗

PubMed2002

Exercise induces angiogenesis but does not alter movement representations within rat motor cortex.

The effects of exercise on the topography of movement representations and blood vessel density within the rat forelimb motor cortex was examined. Adult male rats were allocated to either a Voluntary eXercise (VX) or Inactive Condition (IC). VX animals were housed for 30 days with unlimited access to running wheels while IC animals were housed in standard laboratory cages. VX animals exhibited a progressive increase in the distance traveled per day and ran an average of 58.3 km across the 30-day training period. Microelectrode stimulation was used to derive high resolution maps of the forelimb representations within the motor cortex of animals from both conditions. No significant differences in the area of either distal (wrist/digit) or proximal (elbow/shoulder) movement representations were found between VX and IC animals. However, VX animals did have a significantly greater density of blood vessels within layer V of the forelimb motor cortex. These results demonstrate that increases in forelimb motor activity sufficient to induce cortical angiogenesis does not alter the topography of forelimb movement representations within forelimb motor cortex.

Animals↗

PubMedDate not supplied

Movement parameters and neural activity in motor cortex and area 5.

The relations of ongoing single-cell activity in the arm area of the motor cortex and area 5 to parameters of evolving arm movements in two-dimensional (2D) space were investigated. A multiple linear regression model was used in which the ongoing impulse activity of cells at time t + tau was expressed as a function of the (X, Y) components of the target direction and of position, velocity, and acceleration of the hand at time t, where tau was a time shift (-200 to +200 msec). Analysis was done on 290 cells in the motor cortex and 207 cells in area 5. The time shift at which the highest coefficient of determination (R2) was observed was determined and the statistical significance of the model tested. The median R2 was 0.581 and 0.530 for motor cortex and area 5, respectively. The median shift at which the highest R2 was observed was -90 and +30 msec for motor cortex and area 5, respectively. For most cells statistically significant relations were observed to all four parameters tested; most prominent were the relations to target direction and least prominent those to acceleration.

Animals↗

PubMed1993

Interhemispheric facilitation of the hand area of the human motor cortex.

We investigated interaction of the human bilateral hand motor area using two magnetic stimulators. A conditioning shock over the motor cortex facilitated the response evoked in the ipsilateral first dorsal interosseous muscle by a test shock over the contralateral motor cortex given under the limiting conditions of a small conditioning shock over a very small area and a small test shock. This effect was so weak that it was not elicited under slightly different conditions. We conclude that an excitatory, but weak, connection between strictly homotopic areas of the bilateral hand motor cortices exists in humans.

Adult↗

PubMed2001

Chronic motor cortex stimulation for phantom limb pain: a functional magnetic resonance imaging study: technical case report.

OBJECTIVE AND IMPORTANCE: Chronic motor cortex stimulation has provided satisfactory control of pain in patients with central or neuropathic trigeminal pain. We used this technique in a patient who experienced phantom limb pain. Functional magnetic resonance imaging (fMRI) was used to guide electrode placement and to assist in understanding the control mechanisms involved in phantom limb pain. CLINICAL PRESENTATION: A 45-year-old man whose right arm had been amputated 2 years previously experienced phantom limb pain and phantom limb phenomena, described as the apparent possibility of moving the amputated hand voluntarily. He was treated with chronic motor cortex stimulation. INTERVENTION: Data from fMRI were used pre- and postoperatively to detect shoulder and stump cortical activated areas and the "virtual" amputated hand cortical area. These sites of preoperative fMRI activation were integrated in an infrared-based frameless stereotactic device for surgical planning. Phantom limb virtual finger movement caused contralateral primary motor cortex activation. Satisfactory pain control was obtained; a 70% reduction in the phantom limb pain was achieved on a visual analog scale. Postoperatively and under chronic stimulation, inhibiting effects on the primary sensorimotor cortex as well as on the contralateral primary motor and sensitive cortices were detected by fMRI studies. CONCLUSION: Chronic motor cortex stimulation can be used to relieve phantom limb pain and phantom limb phenomena. Integrated by an infrared-based frameless stereotactic device, fMRI data are useful in assisting the neurosurgeon in electrode placement for this indication. Pain control mechanisms and cortical reorganization phenomena can be studied by the use of fMRI.

Electric Stimulation Therapy↗

PubMed2004

Motor cortex excitability after cerebellar infarction.

BACKGROUND AND PURPOSE: The cerebellum has an influence on motor excitability. We investigated if the location of a cerebellar infarction was crucial for changes of motor cortex excitability and if the electrophysiological findings were correlated with motor performance. METHODS: Transcranial magnetic stimulation was applied to study intracortical inhibition (ICI), intracortical facilitation (ICF), motor thresholds, and corticospinal excitability. Dexterity as a measure of motor performance was tested with the Nine-Hole-Peg Test (9HPT). Ratios (affected/unaffected) were also calculated. RESULTS: ICI and ICF ratios were negatively correlated with 9HPT ratios in all patients (n=9). Compared with an age-matched control group, patients with lesions in the territory of the superior cerebellar artery (SCA) (n=3) or a lesion rostral of the dentate nucleus (n=1) had abnormally enhanced ICI and a loss of ICF (3 patients). Dexterity was impaired in all 4 patients. Motor excitability and motor performance normalized over the subsequent weeks. Patients with an infarct either in the territory of the anterior inferior cerebellar artery (n=2) or in the territory of the posterior inferior cerebellar artery (n=3) displayed motor excitability and motor performance within the normal range. CONCLUSIONS: The superior part of the cerebellum has a strong influence on motor cortex excitability. We suggest that the enhancement of motor inhibition and reduction of motor facilitation is mediated by an impairment of the deep cerebellar nuclei.

Adult↗

PubMed1982

Pattern of projection and physiological properties of cortico-cortical connections from the posterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons lying along the posterior bank of the ansate sulcus and the projection of these neurons to area 4 gamma of the motor cortex of the cat were studied and the following results were obtained: (1) Short latency antidromic responses were recorded from neurons along the medial-lateral bank of the posterior ansate sulcus following intracortical microstimulation (ICMS) delivered to motor cortex, area 4 gamma. (2) The posterior ansate region projects topographically to the motor cortex. Neurons in the most medial part of the ansate region project to the medial part of 4 gamma, while neurons in the central and lateral parts of the ansate region project to the more lateral parts of area 4 gamma. (3) In 33 cases, receptive field information was available for both the antidromically activated ansate neuron and from neurons around the stimulating site in 4 gamma. In 58% of the cases, both cortical sites received afferent input from within the same part of the periphery. (4) Afferent input to the motor cortex was examined following combined ablations of the primary somatosensory cortex (SI) and third somatosensory cortex (SIII) including all of area 5. We conclude that the integrity of these cortical regions is not necessary for afferent input to reach the motor cortex.

Afferent Pathways↗

PubMed2000

Training-induced changes of motor cortex representations in stroke patients.

OBJECTIVE: To study changes in motor cortex representations after a single session of physiotherapy in stroke patients. METHODS: TMS mapping was used to evaluate the motor output map of the abductor pollicis brevis (APB) in both hemispheres. Stroke patients (4-8 weeks after the infarction) were studied prior to a training session aimed at improving dexterity and 1 h and 1 day after the training. RESULTS: Prior to the training, the APB representation area in the affected hemisphere was significantly smaller than on the non-affected side. After therapy, the cortical motor output to the paretic APB was significantly enlarged, and motor function was improved. One day later, these effects were partially reversed. Motor thresholds remained significantly increased in the affected hemisphere before and after the therapy. CONCLUSION: A single session of physiotherapy produces a use-dependent enlargement of motor cortex representations paralleled by an improvement of motor function in stroke patients.

Adult↗

PubMed2001

Inhibition of ipsilateral motor cortex during phasic generation of low force.

OBJECTIVE: To study the effect of different types of unilateral pinch grips on excitability of the ipsilateral motor cortex. METHODS: In 9 healthy volunteers, transcranial magnetic stimuli (TMS) were applied over one motor cortex while the subjects performed either phasic or tonic ipsilateral pinch grips with different force levels (range 1-40% maximum voluntary contraction, MVC). Motor evoked potentials (MEP) were recorded from the relaxed contralateral first dorsal interosseous muscle (FDI) and were compared to MEPs obtained during muscle relaxation of both hands. In additional experiments, transcranial electrical stimuli (TES) were administered and F waves were recorded after electrical stimulation of the ulnar nerve. RESULTS: Phasic pinch grips with low force (1 and 2% MVC) induced a significant decrease of TMS-induced MEP amplitudes. The effect lasted for about 100 ms after reaching the force level and was similar for both right and left-handed pinch grips. TES-induced MEPs and F waves remained unchanged. In contrast, tonic contractions (20 and 40% MVC) enhanced MEPs in the homologous FDI. CONCLUSIONS: Phasic pinch grips with low force inhibit the motor cortex responsible for the contralateral homologous hand muscle. This effect, which is probably mediated transcallosally, might act at the level of the motor cortex.

Adult↗

PubMed1992

Effects of preliminary perceptual output on neuronal activity of the primary motor cortex.

Observations of single neurons in the primary motor cortex of 1 monkey provided evidence that preliminary perceptual information reaches the motor system before perceptual analysis is complete. Neurons were recorded during a task in which 1 stimulus was assigned to a wrist flexion response and another was assigned to wrist extension. Two stimuli were assigned to a no-go response; each was visually similar to either the flexion or the extension stimulus. When a no-go stimulus was presented, neurons responded with weaker versions of the discharge patterns exhibited to the visually similar stimulus requiring a movement, suggesting that neurons receive partial perceptual information favoring that movement. Functionally separable neuronal populations were identified, and differences in the activations of these provide evidence about the functional effects of preliminary perceptual output on movement control processes.

Animals↗

PubMed1996

Comparison of neuronal activity in the supplementary motor area and primary motor cortex.

Neuronal activity in the supplementary motor area (SMA) and primary motor cortex (MI) have been compared in many experiments during performance of many different motor tasks. On one hand, the activity in both areas may appear similar, especially when the motor task is simple. On the other hand, if the motor tasks are more demanding, neuronal activity in the SMA exhibits a variety of complex relationship to many different aspects of motor behavior, while the activity in MI is mostly related to execution of motor task itself. Of particular interest is the neuronal activity in the SMA during preparation and execution of motor tasks when no external cues for the retrieval of appropriate motor act is available. Temporal sequencing of multiple movements is a typical example of the kind of motor task that requires profound activity in the SMA.

Animals↗

PubMed2000

Short latency inhibition of human hand motor cortex by somatosensory input from the hand.

1. EMG responses evoked in hand muscles by transcranial stimulation over the motor cortex were conditioned by a single motor threshold electrical stimulus to the median nerve at the wrist in a total of ten healthy subjects and in five patients who had electrodes implanted chronically into the cervical epidural space. 2. The median nerve stimulus suppressed responses evoked by transcranial magnetic stimulation (TMS) in relaxed or active muscle. The minimum interval between the stimuli at which this occurred was 19 ms. A similar effect was seen if electrical stimulation was applied to the digital nerves of the first two fingers. 3. Median or digital nerve stimulation could suppress the responses evoked in active muscle by transcranial electrical stimulation over the motor cortex, but the effect was much less than with magnetic stimulation. 4. During contraction without TMS, both types of conditioning stimuli evoked a cutaneomuscular reflex that began with a short period of inhibition. This started about 5 ms after the inhibition of responses evoked by TMS. 5. Recordings in the patients showed that median nerve stimulation reduced the size and number of descending corticospinal volleys evoked by magnetic stimulation. 6. We conclude that mixed or cutaneous input from the hand can suppress the excitability of the motor cortex at short latency. This suppression may contribute to the initial inhibition of the cutaneomuscular reflex. Reduced spinal excitability in this period could account for the mild inhibition of responses to electrical brain stimulation.

Adult↗

PubMed1993

Differences in the recovery rate of a learned forelimb movement after ablation of the motor cortex in right and left hemisphere in white rats.

After ablation of the motor cortex contralateral to the preferred limb, rats were forced to use this limb in grasping food out of a horizontal tube by restraining the non-preferred foreleg with a bracelet. In a right-handed rat the motor behaviour is less impaired and the recovery is better after a left hemisphere lesion in comparison with a left-handed rat after a right hemisphere lesion. This difference is primarily the time needed to use the limb in reaching for seed (testperiod 3) and the total time needed for 10 successive seizings of seed (testperiod 5). Surprisingly, the differences in the course of recovery do not correlate with the degree of preoperative limb preference: the initially ambidextrous rate also show the same differences in results of the motor cortex ablation in left and right hemisphere. However, in the group of initially consistent ambidextrous rats, after 10 weeks of tests with a restrained forelimb, the testing under unrestrained free conditions shows a gradual decrease in the induced limb preference and a shift to the use of the foreleg contralateral to the intact hemisphere, while in contrast the initially consistent left- or right-handed rats preserve the limb preference under the unrestrained testing conditions. Therefore the degree of initial preference still influences the choice of limb after motor cortex ablation and intensive training to use the 'damaged' limb.

Animals↗

PubMed2004

Learning modifies subsequent induction of long-term potentiation-like and long-term depression-like plasticity in human motor cortex.

Learning may alter rapidly the output organization of adult motor cortex. It is a long-held hypothesis that modification of synaptic strength along cortical horizontal connections through long-term potentiation (LTP) and long-term depression (LTD) forms one important mechanism for learning-induced cortical plasticity. Strong evidence in favor of this hypothesis was provided for rat primary motor cortex (M1) by showing that motor learning reduced subsequent LTP but increased LTD. Whether a similar relationship exists in humans is unknown. Here, we induced LTP-like and LTD-like plasticity in the intact human M1 by an established paired associative stimulation (PAS) protocol. PAS consisted of 200 pairs of electrical stimulation of the right median nerve, followed by focal transcranial magnetic stimulation of the hand area of the left M1 at an interval equaling the individual N20 latency of the median nerve somatosensory-evoked cortical potential (PAS(N20)) or N20-5 msec (PAS(N20-5)). PAS(N20) induced reproducibly a LTP-like long-lasting (>30 min) increase in motor-evoked potentials from the left M1 to a thumb abductor muscle of the right hand, whereas PAS(N20-5) induced a LTD-like decrease. Repeated fastest possible thumb abduction movements resulted in learning, defined by an increase in maximum peak acceleration of the practiced movements, and prevented subsequent PAS(N20)-induced LTP-like plasticity but enhanced subsequent PAS(N20-5)-induced LTD-like plasticity. The same number of repeated slow thumb abduction movements did not result in learning and had no effects on PAS-induced plasticity. Findings support the view that learning in human M1 occurs through LTP-like mechanisms.

Adult↗

PubMed1997

Differential effects of abnormal tactile experience on shaping representation patterns in developing and adult motor cortex.

This study investigates the influence of early somatosensory experience on shaping movement representation patterns in motor cortex. Electrical microstimulation was used to map bilaterally the motor cortices of adult rats subjected to altered tactile experience by unilateral vibrissa trimming from birth (birth-trimmed group) or for comparable periods that began in adulthood (adult-trimmed group). Findings demonstrated that (1) vibrissa trimming from birth, but not when initiated in adulthood, led to a significantly smaller-sized primary motor cortex (M1) vibrissa representation in the hemisphere contralateral to the trimmed vibrissae, with no evidence for concomitant changes in size of the adjacent forelimb representation or the representation of the intact vibrissae in the opposite (ipsilateral) hemisphere; (2) in the contralateral hemispheres of the birth-trimmed group, an abnormal pattern of evoked vibrissa movement was evident in which bilateral or ipsilateral (intact) vibrissa movement predominated; (3) in both hemispheres of the birth-trimmed group, current thresholds for eliciting movement of the trimmed vibrissa were significantly lower than normal; and (4) in the adult-trimmed group, but not in the birth-trimmed group, there was a decrease bilaterally in the relative frequency of dual forelimb-vibrissa sites that form the common border between these representations. These results show that sensory experience early in life exerts a significant influence in sculpting motor representation patterns in M1. The mature motor cortex is more resistant to the type and magnitude of influence that tactile experience has on developing M1, which may indicate that such an influence is constrained by a developmentally regulated critical period.

Age Factors↗

PubMed1999

On the focal nature of inhibition and facilitation in the human motor cortex.

OBJECTIVE: To find the area of the human cortex from which inhibition and facilitation of corticospinal neurons could be obtained. METHODS: A patient with seizures had an array of 64 electrodes placed over the left fronto-temporal cortex. The motor evoked potential (MEP) elicited by stimulating through one pair of electrodes was conditioned by stimuli that were subthreshold for a MEP given through adjacent pairs of electrodes. RESULTS: The MEP recorded over the right abductor pollicis brevis produced by stimulating over the hand area of the left cortex could be inhibited (at intervals less than 5 ms) and facilitated (at intervals greater than 5 ms) by subthreshold conditioning stimuli delivered through neighbouring pairs of electrodes. The inhibition and facilitation were only obtained when the conditioning stimuli were delivered within 1-2 cm of the test site. The sites producing inhibition and facilitation were not identical. Conditioning stimuli over the face area did not inhibit the MEP produced by stimulating the hand area or vice versa. CONCLUSION: The inhibition and facilitation of corticospinal neurons projecting to a given muscle arise from small areas close to those corticospinal neurons.

Electric Stimulation↗