PubMed Health⌕ Search

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 145 records · Page 8Linked to original sources
PubMed1993

Projection from the sensory to the motor cortex is important in learning motor skills in the monkey.

1. The projection from the somatosensory cortex to the primary motor cortex has been proposed to play an important role in learning novel motor skills. This hypothesis was examined by studying the effects of lesions to the sensory cortex on learning of new motor skills. 2. We used two experimental paradigms to reveal the effects of lesions on learning of new motor skills. One task was to catch a food pellet falling at various velocities. The other task was to catch a food pellet from a rotating level. Both tasks required acquisition of novel motor skills. 3. The training was started after a lesion of the hand area in the somatosensory cortex of one hemisphere. In both tasks, monkeys had severe difficulty in learning the new skills with the hand contralateral to the ablated somatosensory cortex, compared with the hand contralateral to the intact hemisphere. 4. After acquisition of the motor skill in the hand contralateral to intact hemisphere, lesion of the somatosensory cortex hand area did not abolish the learned motor skill. 5. In control experiments, monkeys were trained to pick up a food pellet from a rotating board. This task did not necessitate acquisition of new motor skills, but could be performed by utilizing existing motor skills. Lesion in the somatosensory cortex before or after the training did not affect the execution of this task by either hand. 6. It is concluded that the corticocortical projection from the somatosensory to the motor cortex plays an important role in learning new motor skills, but not in the execution of existing motor skills.

Afferent Pathways↗
PubMedDate not supplied

The effects of atropine microinjections into the motor cortex of rats on the development of a motor habit.

Acetylcholine modulates the responses of motor cortex neurons during learning. Studies were carried out on the effects of atropine microinjections into the motor cortex on the development of a habit consisting of procuring food with the forelimbs in freely mobile rats. Animals received unilateral intracortical injections of atropine (5 and 15 micrograms in 0.6 microliter over 40 sec) in the forelimb representation area of the motor cortex. Rats were trained to procure food from a horizontal tube, using the forelimb contralateral to the injection site. Data were obtained which suggested that atropine has a dose-dependent effect on the development of this movement habit. The general effect of atropine doses consisted of suppressing the inhibition of concurrent movements during learning. The higher atropine concentration had a depressive effect on the initiation of the learned movement.

Animals↗
PubMed2004

Functional recovery after lesions of the primary motor cortex.

After a lesion in the motor cortex of an adult primate, are cortical motor maps reorganized? This important question has attracted much interest throughout the past decade. In human subjects, substantial progress has resulted from the use of noninvasive imaging and stimulation techniques. For example, there is recent, well-accepted, albeit indirect evidence that following such a lesion on one side of the human brain, a dramatic reorganization of the hand representation occurs within either the ipsilateral primary motor cortex, nonprimary motor areas or both. The contribution of contralateral motor areas to functional recovery of the paretic hand remains uncertain, however, because of the lack of direct confirmatory evidence obtained from experiments undertaken on nonhuman primates. A better understanding of how the brain selects the optimal strategy for functional recovery following cortical lesions, and the neuronal mechanisms underlying cortical plasticity, will be important challenges for the next decade. To this end, the purpose of the present chapter is to provide an update on what is truly known about the functional recovery that takes place after a lesion in the primary motor cortex of both the nonhuman primate and the human. It bears emphasis that work on these fundamental issues is an essential prerequisite to the development of improved therapeutic and rehabilitation procedures for the brain-injured human.

Animals↗
PubMed1993

The effects of localized inactivation of somatosensory cortex, area 2, on the cat motor cortex.

Direct corticocortical afferents to the primary motor cortex (MI) originate in area 2 and area 3a of the primary somatosensory cortex (SI). The functional and morphological characteristics of the two pathways indicate that they relay different sensory signals to MI. The role of area 2 in relaying peripheral information to the cat MI was studied using electrophysiological techniques. Neurons that responded to stimulation of peripheral receptive fields on the contralateral forepaw were identified in MI by extracellular recordings. In area 2 of SI, neurons with the same receptive field modality and location as those in MI were also identified. Field potentials to electrical stimulation of the peripheral receptive field were recorded at the somatotopically matched sites in both MI and SI. Neuronal activity at the recording site in area 2 was blocked by injection of lidocaine, a local anesthetic. Changes in MI and area 2 responses were monitored before and after inactivation of area 2. Neuronal activity near the injection site was abolished, and evoked potentials (EPs) in area 2 were considerably diminished immediately following the injection. In MI, spontaneous activity levels were altered at some sites, but overall these changes were not significant. MI EPs recorded in response to peripheral stimulation were altered, and various patterns of change were noted in the early and late phases of the EPs. Changes often occurred in only one phase of the response. In some EPs, both early and late phases changed, but the direction and magnitude of change in one phase were not always linked to such changes in the other phase. Both increases and decreases in the amplitude and the area of each phase were observed. The morphological characteristics of the projection were reviewed and related to the findings in the study. It is proposed that inherent features of the pathway may account for the variable patterns of change that were observed.

Animals↗
PubMed2002

Functional connectivity of human premotor and motor cortex explored with repetitive transcranial magnetic stimulation.

Connections between the premotor cortex and the primary motor cortex are dense and are important in the visual guidance of arm movements. We have shown previously that it is possible to engage these connections in humans and to measure the net amount of inhibition/facilitation from premotor to motor cortex using single-pulse transcranial magnetic stimulation (TMS). The aim of this study was to test whether premotor activation can affect the excitability of circuits within the primary motor cortex (M1) itself. Repetitive TMS (rTMS), which is known to produce effects that outlast the train at the site of stimulation, was given for 20 min at 1 Hz over premotor, primary motor, and sensory areas of cortex at an intensity of 80% of the active motor threshold for the motor hand area. The excitability of some corticocortical connections in M1 was probed by using paired-pulse testing of intracortical inhibition (ICI) and intracortical facilitation (ICF) with a coil placed over the motor cortex hand area. rTMS over the premotor cortex, but not other areas, changed the time course of the ICI/ICF for up to 1 hr afterward without affecting motor thresholds or motor-evoked potential recruitment. The cortical silent period was also shortened. The implication is that rTMS at a site distant from the motor cortex can change the excitability of circuits intrinsic to the motor cortex.

Adult↗
PubMed1990

Modulation of somatosensory evoked responses in the primary somatosensory cortex produced by intracortical microstimulation of the motor cortex in the monkey.

Previous studies have shown that the amplitude of somatosensory evoked potentials is diminished prior to, and during, voluntary limb movement. The present study investigated the role of the motor cortex in mediating this movement-related modulation in three chronically prepared, awake monkeys by applying low intensity intracortical microstimulation (ICMS) to different sites within the area 4 representation of the arm. Air puff stimuli were applied to the contralateral arm or adjacent trunk at various delays following the ICMS. Somatosensory evoked potentials were recorded from the primary somatosensory cortex, areas 1 and 3b, with an intracortical microelectrode. The principal finding of this study was that very weak ICMS, itself producing at most a slight, localized, muscle twitch, produced a profound decrease in the magnitude of the short latency component of the somatosensory evoked potentials in the awake money. Higher intensities of ICMS (suprathreshold for eliciting electromyographic (EMG) activity in the "target" muscle, i.e. that muscle activated by area 4 stimulation) were more likely to decrease the evoked response and produced an even greater decrease. The modulation appeared to be, in part, central in origin since (i) it preceded the onset of EMG activity in 23% of experiments, (ii) direct stimulation of the muscle activated by ICMS, which mimicked the feedback associated with the small ICMS-induced twitch, was often ineffective and (iii) the modulation was observed in the absence of EMG activity. Peripheral feedback, however, may also make a contribution. The results also indicate that the efferent signals from the motor cortex can diminish responses in the somatosensory cortex evoked by cutaneous stimuli, in a manner related to the somatotopic order. The effects are organized so that the modulation is directed towards those neurones serving skin areas overlying, or distal to, the motor output.

Animals↗
PubMed1983

Neonatal motor cortex lesions in the rat: absence of sparing of motor behaviors and impaired spatial learning concurrent with abnormal cerebral morphogenesis.

Rats with removal of the motor cortex in adulthood were compared behaviorally and neuroanatomically with rats with similar removals at 4 days of age. The results suggest that neonatal ablation of the motor cortex of rats is more debilitating behaviorally than similar injury in adulthood and produces abnormal morphogenesis of the posterior neocortex. Neonatal lesions of the motor cortex produced more chronic abnormalities in movements of the distal effectors that accompany adult lesions (tongue, snout, and digit use) and, in addition, produced abnormalities in limb placement on a narrow beam and a significant impairment in spatial learning, neither of which is associated with adult lesions. When the brains of neonatally operated rats were compared with those of control rats or rats operated on in adulthood, there were striking differences. Although the area of cavity appeared smaller in the neonatal operates, their brains weighed less, the neocortex was thinner, and the cross-sectional area of the remaining cortex was reduced, when compared with those of the adult-operated group. It is suggested that studies of the acquisition of various neuropsychological learning tasks may have greatly overestimated the degree of sparing following anterior neocortical lesions in rats.

Animals↗
PubMed2004

Skilled motor learning does not enhance long-term depression in the motor cortex in vivo.

Learning of motor skills may occur as a consequence of changes in the efficacy of synaptic connections in the primary motor cortex. We investigated if learning in a reaching task affects the excitability, short-term plasticity, and long-term plasticity of horizontal connections in layers II-III of the motor cortex. Because training in this task requires animals to be food-deprived, we compared the trained animals with similarly food-deprived untrained animals and normal controls. The results show that the excitability, short-term plasticity, and long-term plasticity of the studied horizontal connections were unaffected by motor learning. However, stress-related effects produced by food deprivation and handling significantly enhanced the expression of long-term depression in these pathways. These results are compatible with the hypothesis that the acquisition of a complex motor skill produces bi-directional changes in synaptic strength that are distributed throughout the complex neural networks of motor cortex, which remains synaptically balanced during learning. The results are incompatible with the idea that learning causes large unidirectional changes in the population response of these neural networks, which may occur instead during certain behavioral states, such as stress.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1989

Digit-muscle responses evoked from multiple intracortical foci in monkey precentral motor cortex.

1. The precentral motor cortex, including the anterior bank of the central sulcus of monkey (Macaca fuscata), was systemically penetrated with microelectrodes to determine the spatial organization of the microexcitable cortical elements that can produce responses in digit muscles. 2. At 200-microns intervals on each electrode track, low-current intracortical microstimuli were delivered and the muscle responses evoked from four digit muscles were recorded. The responses, obtained with 5, 8, 15, and 25 microA, were quantified and plotted on a map displaying an unfolded view of the precentral gyrus. 3. For all four muscles studied [first interosseus, thenar, extensor digitorum communis (EDC) and flexor digitorum profundus (FDP)], the effective stimulus points evoking muscle responses at a current of 5 microA were scattered over wide areas. The low-threshold foci, largely buried in the anterior bank of the central sulcus but partly extending to a region rostral to the sulcus, were found in multiple spots separated by a few millimeters. 4. Stimulation of individual sites at a current of 5 microA often evoked responses in several different muscles. Antagonist muscles were frequently coactivated. 5. A three-dimensional display of the distribution of response magnitude evoked from the precentral cortex indicates several peaks for each digit muscle. The peaks were either sharply demarcated from surrounding areas of minimal responses or gradually shifted into regions of low-grade responses. 6. Taken together, the data suggest that the digit area of motor cortex does not have a simple organization in which each muscle is represented by a single focus. Rather, each muscle has multiple foci that have varying degrees of efficacy in producing responses and with variable overlap onto foci of other muscles.

Animals↗
PubMed1979

Peripheral input pathways projecting to the motor cortex in the cat.

The possibility that the motor cortex receives peripheral input directly from the thalamus was examined using the evoked potential method and the following results were obtained. Potentials in the motor cortex evoked by stimulation of superficial radial (SR) or group II deep radial (DR) nerve were neither abolished nor delayed by ablation of the sensory cortex. Potentials in the motor cortex evoked by stimulation of group II DR nerve were most severely reduced by interruption of the spinocervcial tract. Potentials evoked by stimulation of SR nerve were more severely reduced in the sensory cortex than in the motor cortex by section of the dorsal funiculus or cooling of the cuneate nucleus. The size of evoked potentials in the motor cortex increased rapidly when stimulus intensity to DR nerve exceeded the threshold to group II fibers. The results suggest that some inputs from the SR and group II DR nerves reach the motor cortex without a relay through the sensory cortex.

Animals↗
PubMed2005

Dissociation of sensorimotor deficits after rostral versus caudal lesions in the primary motor cortex hand representation.

Primary motor cortex (M1) has traditionally been considered a motor structure. Although neurophysiologic studies have demonstrated that M1 is also influenced by somatosensory inputs (cutaneous and proprioceptive), the behavioral significance of these inputs has yet to be fully defined in primates. The present study describes differential sensory-related deficits after small ischemic lesions in either the rostral or caudal subregion of the M1 hand area in a nonhuman primate. Squirrel monkeys retrieved food pellets out of different sized wells drilled into a Plexiglas board. Before the lesion, monkeys retrieved pellets by directing the hand to the well, inserting fingers directly into it, and extracting the pellet. After a lesion to the rostral portion of M1, monkeys frequently failed to direct the hand accurately to the well. Instead, fingers contacted the surface of the board outside the well before entering the well. These aiming errors are consistent with both the large amount of proximal motor outputs and the predominant proprioceptive inputs of rostral M1. Overall, these aiming errors are suggestive of dysfunctional processing of proprioceptive information or the failure to integrate proprioceptive information with motor commands. In contrast, after a lesion to the caudal portion of M1, monkeys frequently examined their palm visually for the presence of the pellet after an attempted retrieval. These errors are consistent with both the large amount of distal motor outputs and the predominant cutaneous inputs of caudal M1. Thus these errors are suggestive of a deficit in processing of cutaneous information or the failure to integrate cutaneous information with motor commands. Rostral and caudal M1 lesions result in different deficits in sensory-dependent motor control that appear to correlate with broad segregation of motor outputs and previously described sensory inputs of M1.

Animals↗
PubMed1989

Long-term potentiation in the motor cortex.

Long-term potentiation (LTP) is a model for learning and memory processes. Tetanic stimulation of the sensory cortex produces LTP in motor cortical neurons, whereas tetanization of the ventrolateral nucleus of the thalamus, which also projects to the motor cortex, does not. However, after simultaneous high-frequency stimulation of both the sensory cortex and the ventrolateral nucleus of the thalamus, LTP of thalamic input to motor cortical neurons is induced. This associative LTP occurs only in neurons in the superficial layers of the motor cortex that receive monosynaptic input from both the sensory cortex and the ventrolateral nucleus of the thalamus. Associative LTP in the motor cortex may constitute a basis for the retention of motor skills.

Animals↗
PubMed1976

Somatotopic localization in cat motor cortex.

Punctate intracortical stimulation of the motor cortex (areas 4 and 6), with parallel observation of the induced movements, permits description of a fine somatotopic organization of the motor control areas for different parts of the musculature in freely moving adult cats. The results show that movements produced by electrical stimulation of the motor cortex are always single and non-repetitive, regardless of the duration and intensity of the stimulation. These movements are restricted to a very precise part of the musculature, and experiments show that this localization is related to the exact position of the tip of the stimulating electrode in the motor cortex. Other experimental data show that motor responses which disturb the animal's equilibrium are accompanied by postural adjustments. Stimulation of the cerebral cortex permits the definition of a separate motor control area for each part of the cat musculature, with an individual control area for each of the joints of the forelimb. This was not possible for the hindlimb, which is always activated in its entirety. These results establish a new representation of the somatotopic organization of the cat motor cortex. This diagram shows that area 6 controls the more axial parts of the musculature, while area 4 controls the proximal and distal parts of the limb muscles. This map was compared to numerous previous data on the somatotopic organization in the cat motor cortex, especially to the map of Woolsey.

Animals↗
PubMed2004

Comparison between short train, monophasic and biphasic repetitive transcranial magnetic stimulation (rTMS) of the human motor cortex.

OBJECTIVE: To compare motor evoked potentials (MEPs) elicited by short train, monophasic, repetitive transcranial magnetic stimulations (rTMS) with those by short train, biphasic rTMS. METHODS: Subjects were 13 healthy volunteers. Surface electromyographic (EMG) responses were recorded from the right first dorsal interosseous muscle (FDI) in several different stimulation conditions. We gave both monophasic and biphasic rTMS over the motor cortex at a frequency of 0.5, 1, 2 or 3Hz. To study excitability changes of the spinal cord, we also performed 3Hz rTMS at the foramen magnum level [Ugawa Y, Uesaka Y, Terao Y, Hanajima R, Kanazawa I. Magnetic stimulation of corticospinal pathways at the foramen magnum level in humans. Ann Neurol 1994;36:618-24]. We measured the size and latency of each of 20 MEPs recorded in the different stimulation conditions. RESULTS: 2 or 3Hz stimulation with either monophasic or biphasic pulses evoked MEPs that gradually increased in amplitude with the later MEPs being significantly larger than the earlier ones. Monophasic rTMS showed much more facilitation than biphasic stimulation, particularly at 3Hz. Stimulation at the foramen magnum level at 3Hz elicited fairly constant MEPs. CONCLUSIONS: The enhancement of cortical MEPs with no changes of responses to foramen magnum level stimulation suggests that the facilitation occurred at the motor cortex. We hypothesize that monophasic TMS has a stronger short-term effect during repetitive stimulation than biphasic TMS because monophasic pulses preferentially activate one population of neurons oriented in the same direction so that their effects readily summate. Biphasic pulses in contrast may activate several different populations of neurons (both facilitatory and inhibitory) so that summation of the effects is not so clear as with monophasic pulses. When single stimuli are applied, however, biphasic TMS is thought to be more powerful than monophasic TMS because the peak-to-peak amplitude of stimulus pulse is higher and its duration is longer when the same intensity of stimulation (the same amount of current is stored by the stimulator) is used. SIGNIFICANCE: This means that when using rTMS as a therapeutic tool or in research fields, the difference in waveforms of magnetic pulses (monophasic or biphasic) may affect the results.

Adult↗
PubMed2001

Asymmetry of motor cortex excitability during a simple motor task: relationships with handedness and manual performance.

Transcranial magnetic stimulation (TMS) was used to assess the relative contribution of the corticospinal (CS) pathway in activating the first dorsal interosseous (FDI) muscle in each hand of 16 right- (RH) and 16 left-handed (LH) subjects with varied degrees of hand preference. It was hypothesised that asymmetry in corticospinal activation of the two hands may be related to hand preference and interlimb differences in manual performance. Subjects performed isometric index finger abduction at force levels of 0.5 N, 1 N and 2 N while TMS was applied at resting threshold intensity (T), 0.9T, or 0.8T. The amount of contraction-induced facilitation of the muscle evoked potential (MEP) was used as an estimate of corticospinal involvement in the task. Patterns of MEP facilitation in each hand were compared with measures of manual performance (finger tapping speed, Purdue pegboard, maximal FDI strength). Threshold TMS intensities for an MEP in FDI at rest were similar in LH and RH subjects, and did not vary between hands. Facilitation of the MEP with voluntary activation was larger overall on the left side (P<0.05), but the asymmetry was dependent on the degree of lateralisation of hand preference. For subjects with consistent hand preference (either LH or RH), MEP facilitation in active FDI was larger for the left hand. For non-consistent RH subjects, contraction-induced MEP facilitation was larger in the right FDI muscle than the left. Asymmetry of MEP facilitation was not correlated with differences between hands in finger tapping speed or performance in the pegboard task, but was associated with relative differences in FDI strength. MEP facilitation tended to be larger in the stronger FDI muscle of the pair. We conclude that corticospinal involvement in the command for index finger abduction is generally greater when the left hand is used, although in RH subjects the asymmetry is influenced by the degree of lateralisation of hand preference. The corticospinal asymmetry is not related to speed or dexterity of finger movements, but the association with muscle strength suggests that it may be influenced in part by preferential use of one hand for tasks which strengthen the FDI muscle.

Adult↗
PubMed1984

Motor evoked potentials from transcranial stimulation of the motor cortex in humans.

Electrical monitoring of the motor system offers the potential for the detection of injury, the diagnosis of disease, the evaluation of treatment, and the prediction of recovery from damage. Existing evoked potentials monitor one or another sensory modality, but no generally usable motor monitor exists. We have reported a motor evoked potential using direct stimulation of the spinal cord over the motor tracts in cats and in humans. To achieve a less invasive monitor, we used transcranial stimulation over the motor cortex in the cat, thus stimulating the motor cortex. We report here the initial application of this method to humans. A plate electrode over the motor cortex on the scalp and a second electrode on the palate direct a mild current through the motor cortex which will activate the motor pathways. This signal can be recorded over the spinal cord. It can elicit contralateral peripheral nerve and electromyographic signals in the limbs or movements when the appropriate stimulation parameters are used. In clinical use to date, this has been more reliable than the somatosensory evoked potential in predicting motor function in patients where the two tests differed. It offers a number of possibilities for the development of valuable brain and spinal cord monitoring techniques, but requires further animal studies and clinical experience. Studies to date have not demonstrated adverse effects, but evaluation is continuing.

Adult↗