SEARCH · PubMed Health

Results for “Motor Cortex”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources

PubMed2002

Short-term reduction of intracortical inhibition in the human motor cortex induced by repetitive transcranial magnetic stimulation.

Ten healthy subjects and two patients who had an electrode implanted into the cervical epidural space underwent repetitive transcranial magnetic stimulation (rTMS; 50 stimuli at 5 Hz at active motor threshold intensity) of the hand motor area. We evaluated intracortical inhibition before and after rTMS. In healthy subjects, we also evaluated threshold and amplitude of motor evoked potentials (MEPs), duration of cortical silent period and short-latency intracortical facilitation. rTMS led to a short-lasting reduction in the amount of intracortical inhibition in control subjects with a high interindividual variability. There was no significant effect on other measures of motor cortex excitability. Direct recordings of descending corticospinal volleys from the patients were consistent with the idea that the effect of rTMS on intracortical inhibition occurred at the cortical level. Since the level of intracortical inhibition can be influenced by drugs that act on GABAergic systems, this may mean that low-intensity repetitive magnetic stimulation at 5 Hz can selectively modify the excitability of GABAergic networks in the human motor cortex.

Adult↗

PubMedDate not supplied

The facilitatory and depressive effects of iontophoretically applied acetylcholine on different components of neuron responses in the motor cortex of the cat during performance of a conditioned paw positioning reflex.

Iontophoretic application of acetylcholine to neurons in the motor cortex of cats during performance of a conditioned reflex consisting of placing the paw on a support increased neuron excitability and facilitated "extrinsic" connections, resulting in increases in primary responses to electrical stimulation of the parietal region of the cortex, and which was independent of the first effect of suppression, which was seen only in relation to the long-latency components of the response. The functional significance of the differently directed effects of acetylcholine application is indicated by the statistically significant changes in motor reaction times seen in some experiments, which were in the same direction as changes in neuronal responses in the same experiments.

Acetylcholine↗

PubMed2006

Modulation of intracortical facilitatory circuits of the human primary motor cortex by digital nerve stimulation.

We investigated the effect of electrical digit stimulation on two different intracortical facilitatory phenomena. Paired-pulse transcranial magnetic stimuli (TMS) with different conditioning stimulus (CS) intensities were applied over the primary motor cortex (M1). Electromyographic (EMG) recordings were made from the relaxed right abductor digiti minimi muscle (ADM). The effect of preceding sensory stimulation applied to the ipsilateral digit V on the conditioning magnetic stimulus was examined. Changing the CS intensity affected the influence of peripheral electrical stimulation on motor evoked potential (MEP) amplitudes evoked by paired pulse TMS. Inhibition induced by ipsilateral digit stimulation was strongest with the lowest CS intensity if MEP amplitudes were evoked by a subthreshold CS followed by a suprathreshold test stimulus (TS) at an interstimulus interval (ISI) of 10 ms. In contrast, inhibition induced by digit stimulation in a paired-pulse paradigm with a suprathreshold first and a subthreshold second stimulus at ISI of 1.5 ms was strongest with the highest CS intensity. These findings suggest that appropriately timed peripheral electrical stimuli differentially modulate facilitatory interactions in the primary motor cortex. They further support the hypothesis that intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) are evoked through different mechanisms.

Abducens Nerve↗

PubMedDate not supplied

[Participation of the motor cortex in the bimanual unloading task: a study by transcranial magnetic stimulation].

Motor potentials of m. biceps brachii evoked by transcranial magnetic stimulation of the contralateral motor cortex have been recorded in postural adjustment during arm unloading in humans. During active unloading, the amplitude of the motor evoked potential decreases simultaneously with the decreasing of the muscle activity. During load keeping, the muscle response changes simultaneously with the load changes. When the other arm has lifted the other load during load keeping, the amplitude of the motor evoked potential decreases in the m. biceps of the keeping arm without muscle activity changes. Passive unloading results in the same changes of the motor evoked potential as active unloading. A possible role of the direct corticospinal volley and the motor command mediated by some subcortical structures in the decrease of the muscle activity preceding active unloading (postural adjustment) is discussed.

Arm↗

PubMed2004

Long-lasting motor cortex disinhibition after short transient ischemic attacks (TIAs) in humans.

Lesion-induced cortical hyperexcitability has been demonstrated in animal models of cerebral ischemia and after human stroke. We used transcranial magnetic stimulation to investigate motor cortex excitability in ten patients who suffered short transient ischemic attacks (TIAs; i.e. duration <60 min) in the week before examination. Intracortical inhibition (ICI) and facilitation (ICF) were assessed using paired-pulse stimulation. Single-pulse stimulation was applied to investigate cortical silent period and transcallosal inhibition. The side affected by the TIA was compared to the normal side of each patient. We found ICI significantly reduced, and a trend towards enhanced ICF on the affected side. All other parameters remained normal. Motor cortex disinhibition may occur after short TIAs in spite of morphologically intact brain tissue. Possibly, these functional changes correlate to the protective neurometabolic mechanisms elicited by short episodes of focal ischemia in animal models and in man.

Adult↗

PubMed2002

A transcranial magnetic stimulation study of information processing in the motor cortex: relationship between the silent period and the reaction time delay.

The present study was aimed at deciphering whether the delay in choice reaction time (RT) and the silent period (SP) caused by transcranial magnetic stimulation (TMS) of the motor cortex in the ongoing electromyogram are due to the same physiological mechanism. To this end, the effect of TMS was studied in 6 healthy volunteers performing a between-hand choice RT task. Specific predictions were derived from a logic inspired from the "postponed stages" hypothesis (Pashler & Johnson, 1989). This logic predicts a correlation between SP duration and RT when the stimulated cortex is involved in the response, and a stronger correlation when the stimulation is delivered later during the RT interval. The effect of TMS on RT was twofold: At early stimulation times, the stimulation shortened the RT and this effect was independent of the involvement of the stimulated motor cortex in the subsequent response. At later stimulation times, TMS had a disruptive effect, provided that the stimulated cortex was involved in the response. When the stimulated cortex was involved in the response, there was a correlation between SP and RT; this correlation was stronger when the stimulation occurred later. In contrast, there was no correlation between these two variables when the stimulated cortex was not involved.

Adult↗

PubMed1985

Contrasting neuronal activity in supplementary and precentral motor cortex of monkeys. I. Responses to instructions determining motor responses to forthcoming signals of different modalities.

The present report contrasts neuronal activity in two motor cortical fields after instructions that determine which of two sensory signals will trigger a movement and which will not. The goal of the study was to determine possible differential roles of the two cortical fields in the process of preparing to move in response to one external cue and to ignore another. Single-cell recordings were made from the supplementary motor area (SMA) and the precentral motor area (PCM) of monkeys trained to perform key-press movements in two different modes. In the auditory mode, an instruction signal warned the animal to prepare to start the movement promptly in response to a forthcoming 1,000-Hz tone burst (trigger signal), but to remain motionless if the signal was vibrotactile (nontrigger signal). In the tactile mode, the trigger and nontrigger signals were reversed: a different instruction signal warned the animal to prepare to perform the key-press movement in response to the vibrotactile cue, but to withhold it in response to the 1,000-Hz tone. The instruction signals were auditory tones of 300 Hz for the auditory mode and 100 Hz for the tactile mode. Out of 259 task-related SMA neurons, 128 (49%) responded to instructions. Three types of instruction responses were observed: 1) 95 neurons showed continuous instruction-induced activity changes lasting until the occurrence of the movement-triggering signal, regardless of whether an intervening nontrigger signal occurred. 2) 24 neurons showed increased activity until the occurrence of the nontriggering signal, after which the activity subsided. When there was no nontrigger signal, the activity increased during a period when the nontrigger signal might have been given. 3) Nine neurons responded with a transient, short-latency discharge after the instruction. The responses of SMA neurons to two instructions were often different. Forty-four SMA neurons exhibited a selective response to only one of the two instructions. In 43 neurons the response was differential, with the magnitude of activity increase or decrease being at least three times greater after one instruction than the other. In the remaining 41 neurons the response was nondifferential. Out of 112 task-related PCM neurons, 25 (22%) responded to the instructions. In the majority of them (21 neurons), the instruction response was nondifferential.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

Motor cortex disinhibition of the unaffected hemisphere after acute stroke.

We studied motor cortex excitability in the nonlesioned hemisphere of patients with a large cortical infarction. Patients with a severe hemiparesis due to a stroke were compared with age-matched, healthy controls. Paired transcranial magnetic stimuli were applied over the unaffected hemisphere to investigate intracortical inhibition and facilitation. In the patient group, intracortical inhibition was reduced. We suggest that this disinhibition is due to an impairment of transcallosal fibers and may affect recovery.

Acute Disease↗

PubMed2000

Residual function in motor cortex contralateral to amputated hand.

OBJECTIVE: To investigate residual function of the motor cortex corresponding to the hand of the amputated arm (MCamp). METHODS: Focal transcranial magnetic stimulation (TMS) of MCamp was performed in 10 patients 22 to 52 years after arm amputation to inhibit tonic muscle contraction in the intact hand ipsilateral to cortex stimulation. RESULTS: In all patients, onset latency, degree, and duration of this inhibition were normal. CONCLUSION: The presence of motor inhibition in the residual hand of amputees originating from the hand motor representation of MCamp indicates residual cortical motor representation of the lost hand irrespective of whether the effect is mediated by commissural or ipsilateral corticospinal connections.

Adult↗

PubMed2002

Motor cortex activation is related to force of squeezing.

Primate studies have demonstrated that motor cortex neurons show increased activity with increased force of movement. In humans, this relationship has received little study during a power grip such as squeezing, and has previously only been evaluated across a narrow range of forces. Functional MRI was performed in eight healthy subjects who alternated between rest and right hand squeezing at one of three force levels. During scanning, motor performances were recorded using a dynamometer. At each force level, activation volume was measured within left sensorimotor cortex, right sensorimotor cortex, and a midline supplementary motor area. In left sensorimotor cortex, % signal change was also assessed. The range of force generated across the three force levels varied from 4.9 N to 276 N. In left sensorimotor cortex, activation volume increased significantly with greater force. The % signal change also increased with greater force and correlated closely with activation volume. In supplementary motor area, activation volume increased significantly with increasing force, but with greater intersubject variability. In right sensorimotor cortex, a trend for larger activation volumes with greater force did not reach significance. The laterality index, an expression of the relative degree of contralateral vs. ipsilateral sensorimotor cortex activation, did not change across the three force levels. Increased force of squeezing is associated with increased contralateral sensorimotor cortex and supplementary motor area activation. This relationship was found across the full spectrum of forces that the human hand is capable of generating. Use of a valid, reliable method for assessing motor behavior during functional MRI may be important to clinical applications.

Adult↗

PubMed2003

Illusory movements of the paralyzed limb restore motor cortex activity.

In humans, limb amputation or brachial plexus avulsion (BPA) often results in phantom pain sensation. Actively observing movements made by a substitute of the injured limb can reduce phantom pain, Proc. R. Soc. London B Biol. Sci. 263, 377-386). The neural basis of phantom limb sensation and its amelioration remains unclear. Here, we studied the effects of visuomotor training on motor cortex (M1) activity in three patients with BPA. Functional magnetic resonance imaging scans were obtained before and after an 8-week training program during which patients learned to match voluntary "movements" of the phantom limb with prerecorded movements of a virtual hand. Before training, phantom limb movements activated the contralateral premotor cortex. After training, two subjects showed increased activity in the contralateral primary motor area. This change was paralleled by a significant reduction in phantom pain. The third subject showed no increase in motor cortex activity and no improvement in phantom pain. We suggest that successful visuomotor training restores a coherent body image in the M1 region and, as a result, directly affects the experience of phantom pain sensation. Artificial visual feedback on the movements of the phantom limb may thus "fool" the brain and reestablish the original hand/arm cortical representation.

Adult↗

PubMed1987

Intracellular injection of phorbol ester increases the excitability of neurons of the motor cortex of awake cats.

The electrophysiological effects of two intracellularly injected phorbol esters (PhEs) which activate protein kinase C, phorbol 12,13-dibutyrate and phorbol 12-myristate 13-acetate, were investigated in neurons of the motor cortex of awake cats. The major finding was that intracellularly injected PhEs increased the excitability of the neurons. This was indicated by (1) an increase in spontaneous firing and depolarizing current-induced spike activity, accompanied by a decrease in the latency and threshold of current-induced spike discharges, (2) a reduction in slow afterhyperpolarizations following action potentials and depolarizing pulses, and (3) the development of bursting activity. Neither increases in input resistance nor depolarization of the resting potential sufficient to account for these excitability changes were found. Increases in the amplitudes of action potentials and their fast afterhyperpolarizations were also observed. All changes occurred within 2-8 min after injection and lasted for 50 min or longer. Control injections of 4 alpha-phorbol 12,13-didecanoate, which does not activate protein kinase C, failed to induce changes in neuronal excitability or in any of the above parameters. We conclude that the excitability of neurons of the motor cortex of the awake cats can be increased by phorbol esters that translocate and activate protein kinase C.

Action Potentials↗

PubMed1982

Physiological properties and pattern of projection of cortico-cortical connections from the anterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons in the postsigmoid gyrus lying along the anterior bank of the ansate sulcus and the pattern of projection of these neurons to the motor cortex, area 4 gamma, were investigated in the cat and the following results were obtained. (1) Neurons lying along the anterior bank of the ansate sulcus receive somatotopically organized afferent input from the skin and deep structures on the contralateral side of the body. (2) Short latency antidromic responses were recorded from all regions along the bank of the sulcus following intra-cortical microstimulation (ICMS) of area 4 gamma. (3) The projection of neurons to area 4 gamma was topographically organized. Neurons in the lateral portions projected to more lateral parts of 4 gamma, whereas neurons in the medial region of the postsigmoid gyrus sent axons to the more medial regions of the motor cortex. (4) In 50 cases, receptive fields were recorded from both the antidromically identified postsigmoid gyrus neuron and from neurons around the activation site in area 4 gamma. In 62% of these instances, both cortical sites received afferent input from within the same part of the periphery.

Animals↗

PubMed2000

[The individual characteristics of the cytoarchitectonics of the human motor cortex (based on computer analysis data)].

Age and individual peculiarities of cytoarchitecture of layer III field 4p, periods of intensive and slow growth of the area of profile fields (APF) of pyramid neurons were established by method of computer analysis of histological preparations of human motor cortex from birth up to 20 yrs. It was shown that the greatest changes of APF of pyramid neurons including their individual parameters occur in field 4 of motor cortex during first three years.

Adolescent↗

PubMed1994

Efferent neurons and suspected interneurons in motor cortex of the awake rabbit: axonal properties, sensory receptive fields, and subthreshold synaptic inputs.

1. Properties of antidromically identified efferent neurons within the cortical representation of the vibrissae, sinus hairs, and philtrum were examined in motor cortex of fully awake adult rabbits. Efferent neurons were tested for both receptive field and axonal properties and included callosal (CC) neurons (n = 31), ipsilateral corticocortical (C-IC) neurons (n = 34) that project to primary somatosensory cortex (S-1), and corticofugal neurons of layer 5 (CF-5) (n = 33) and layer 6 (CF-6) (n = 32) that project to and/or beyond the thalamus. Appropriate collision tests demonstrated that substantial numbers of corticocortical efferent neurons project an axon to both the corpus callosum and to ipsilateral S-1. 2. Suspected interneurons (SINs, n = 37) were also studied. These neurons were not activated antidromically from any stimulus site but did respond synaptically to electrical stimulation of the ventrolateral (VL) thalamus and/or S-1 with a burst of three or more spikes at frequencies from 600 to > 900 Hz. All of these neurons also responded synaptically to stimulation of the corpus callosum. The action potentials of these neurons were much shorter in duration (mean = 0.48 ms), than those of efferent neurons (mean = 0.90 ms). 3. CF-5 neurons differed from CC, C-IC, and CF-6 neurons in their spontaneous firing rates, axonal properties, and receptive field properties. Whereas CF-5 neurons had a mean spontaneous firing rate of 4.1 spikes/s, CC, C-IC, and CF-6 neurons all had mean values of < 1 spike/s. Axonal conduction velocities of CF-5 neurons were much higher (mean = 12.76 m/s) than either CC (1.47 m/s), C-IC (0.97 m/s), or CF-6 (mean = 1.96 m/s) neurons. A decrease in antidromic latency (the "supernormal" period) followed a single prior impulse in most CC, C-IC, and CF-6 neurons but was minimal or absent in CF-5 neurons. Although all but two CF-5 neurons responded to peripheral sensory stimulation, many CC (35%), C-IC (59%), or CF-6 (66%) neurons did not. CC, CF-5, and CF-6 neurons that did not respond to sensory stimulation had significantly lower axonal conduction velocities and spontaneous firing rates than those that responded to such stimulation. 4. Sensory receptive fields of neurons in motor cortex were considerably larger than those observed in S-1 but were similar in size to those seen in secondary somatosensory cortex (S-2).(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1992

Stimulation of three areas of the primary motor cortex interrupts micturition in dogs.

To clarify the area of the motor cortex (M1) in dogs, which corresponds to the cortical area participating in voluntary interruption of micturition in humans, the cortical portions related to the external urethral sphincter were first clarified by recording of somato-sensory evoked potentials, and then systematic cortical stimulation was performed in anesthetized and paralyzed dogs. The hypogastric, pelvic and pudendal nerves innervating the lower urinary tract and rectum were severed to eliminate the secondary reflexes. Five foci were recognized in the cortical potentials evoked after stimulation of the pudendal nerve. These foci existed in the sacral (Sacral-S) and hind leg (Leg-S) areas of the somato-sensory cortex (S1), and in the sacral (Sacral-M), hind leg (Leg-M) and trunk (Abd-M) areas of the M1. Stimulation of the three M1 foci, but not the two S1 foci, provoked centrifugal firings of the pudendal urethral branch. The firings disappeared after cutting of the ipsilateral bulbar pyramis. When the M1 foci were stimulated during the micturition reflex, the reflex discharge of a pelvic vesical branch was interrupted concomitantly with firings of the urethral branch. The interruption was still induced after the pyramidotomy. Pulse train stimulation of these M1 foci reset the cycles (about 2 Hz) in the alternative rhythmic firings of the urethral and vesical branches, which are known to be formed in the pontine micturition center [31,32]. These results suggest that the pyramidal cells in the three M1 foci inhibit the pontine micturition center and concomitantly contract the external urethral sphincter through the pyramidal tract. The possible roles of these M1 foci were discussed.

Animals↗

PubMed1998

Responses of thenar muscles to transcranial magnetic stimulation of the motor cortex in patients with incomplete spinal cord injury.

OBJECTIVE: To investigate changes in electromyographic (EMG) responses to transcranial magnetic stimulation (TMS) of the motor cortex after incomplete spinal cord injury in humans. METHODS: A group of 10 patients with incomplete spinal cord injury (motor level C3-C8) was compared with a group of 10 healthy control subjects. Surface EMG recordings were made from the thenar muscles. TMS was applied with a 9 cm circular stimulating coil centred over the vertex. The EMG responses to up to 50 magnetic stimuli were rectified and averaged. RESULTS: Thresholds for compound motor evoked potentials (cMEPs) and suppression of voluntary contraction (SVC) elicited by TMS were higher (p < 0.05) in the patient group. Latency of cMEPs was longer (p < 0.05) in the patient group in both relaxed (controls 21.3 (SEM 0.5) ms; patients 27.7 (SEM 1.3) ms) and voluntarily contracted (controls 19.8 (SEM 0.5) ms; patients 27.6 (SEM 1.3) ms) muscles. The latency of SVC was longer (p < 0.05) in the patients (51.8 (SEM 1.8) ms) than in the controls (33.4 (SEM 1.9) ms). The latency difference (SVC-cMEP) was longer in the patients (25.3 (SEM 2.4) ms) than in the controls (13.4 (SEM 1.6) ms). CONCLUSION: The longer latency difference between cMEPs and SVC in the patients may reflect a weak or absent early component of cortical inhibition. Such a change may contribute to the restoration of useful motor function after incomplete spinal cord injury.

Adult↗

PubMed1999

Limited functional grouping of neurons in the motor cortex hand area during individuated finger movements: A cluster analysis.

Primary motor cortex (M1) hand area neurons show patterns of discharge across a set of individuated finger and wrist movements so diverse as to preclude classifying the neurons into functional groups on the basis of simple inspection. We therefore applied methods of cluster analysis to search M1 neuronal populations for groups of neurons with similar patterns of discharge across the set of movements. Populations from each of three monkeys showed a large group of neurons the discharge of which increased for many or all of the movements and a second small group the discharge of which decreased for many or all movements. Two to three other small groups of neurons that discharged more specifically for one or two movements also were found in each monkey, but these groups were less consistent than the groups with broad movement fields. The limited functional grouping of M1 hand area neurons suggests that M1 neurons act as a network of highly diverse elements in controlling individuated finger movements.

Algorithms↗