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 1,279 records · Page 71Linked to original sources
PubMed2006

Local field potential spectral tuning in motor cortex during reaching.

In this paper, intracortical local field potentials (LFPs) and single units were recorded from the motor cortices of monkeys (Macaca fascicularis) while they preformed a standard three-dimensional (3-D) center-out reaching task. During the center-out task, the subjects held their hands at the location of a central target and then reached to one of eight peripheral targets forming the corners of a virtual cube. The spectral amplitudes of the recorded LFPs were calculated, with the high-frequency LFP (HF-LFP) defined as the average spectral amplitude change from baseline from 60 to 200 Hz. A 3-D linear regression across the eight center-out targets revealed that approximately 6% of the beta LFPs (18-26 Hz) and 18% of the HF-LFPs were tuned for velocity (p-value < 0.05), while 10% of the beta LFPs and 15% of the HF-LFPs were tuned for position. These results suggest that a multidegree-of-freedom brain-machine interface is possible using high-frequency LFP recordings in motor cortex.

Animals↗
PubMed2004

Short-term modulation of regional excitability and blood flow in human motor cortex following rapid-rate transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) of the human primary motor cortex (M1) provides a means of inducing lasting changes in cortical excitability and synaptic activity. Here we combined rTMS with positron emission tomography of regional cerebral blood flow (rCBF) to examine how an rTMS-induced change in intracortical excitability of inhibitory circuits affects regional synaptic activity. In a first set of experiments, we gave 150 biphasic pulses of 5 Hz rTMS at 90% of active motor threshold to left M1 and used single- and paired-pulse TMS to assess the conditioning effects of rTMS on motor cortical excitability at rest. rTMS conditioning led to a selective decrease in short-latency intracortical inhibition (SICI) without affecting short-latency intracortical facilitation or corticospinal excitability. The decrease in SICI lasted for approximately 8 min. In a second experiment, we used the same rTMS protocol and measured changes in regional synaptic activity (as indexed by rCBF) during and for up to 14 min after the end of rTMS. Subthreshold 5 Hz rTMS induced a region-specific increase in resting rCBF in the stimulated M1 lasting approximately 8 min. These results suggest that in the stimulated M1, temporary attenuation of SICI is paralleled by an increase in synaptic activity, consistent with reduced efficacy of intracortical GABA(A)-ergic synapses. The present findings demonstrate that short trains of low-intensity 5 Hz rTMS can be used to induce a transient change in function within a distinct cortical area. This opens up new possibilities for studying acute reorganization at the systems level in the intact human brain.

Adult↗
PubMed1967

Responses of the pyramidal tract to stimulation of the baboon's motor cortex.

1. The arm area of the baboon's precentral motor cortex was stimulated by brief surface-anodal pulses, and the discharge of the corticospinal tract (the ;pyramidal tract waves') was recorded by an electrode resting on the dorsolateral surface of the cervical spinal cord.2. Some properties of the pyramidal tract waves were described, and they were also studied in relation to the firing of single cortico spinal fibres.3. The results led to the conclusion that the later pyramidal tract waves (the ;I waves') were almost exclusively due to a semi-synchronous repetitive discharge of the same fast cortico spinal fibres as those responsible for the initial wave (the ;D wave').4. Some problems concerning the origin and significance of the I waves were discussed.

Action Potentials↗
PubMed2002

Neuronal populations in primary motor cortex encode bimanual arm movements.

Previous studies have shown that activity of neuronal populations in the primary motor cortex (MI), processed by the population vector method, faithfully predicts upcoming movements. In our previous studies we found that single neurons responded differently during movements of one arm vs. combined movements of the two arms. It was, therefore, not clear whether the population vector approach could produce reliable movement predictions also for bimanual movements. This study tests this question by comparing the predictive quality of population vectors for unimanual and bimanual arm movements. We designed a bimanual motor task that requires coordinated movements of the two arms, in which each arm may move in eight directions, and recorded single unit activity in the MI of two rhesus (Macaca mulatta) monkeys during the performance of unimanual and bimanual arm movements. We analysed the activity of 212 MI cells from both hemispheres and found that, despite bimanual related activity, the directional tuning and preferred directions of most cells were preserved in unimanual and bimanual movements. We demonstrate that population vectors, constructed from the activity of MI cells, predict accurately the direction of movement both for unimanual and for bimanual movements even when the two arms move simultaneously in different directions.

Action Potentials↗
PubMed1993

Topographic mapping of human motor cortex with transcranial magnetic stimulation: Homunculus revisited.

The purpose of this study was to non-invasively evaluate the homuncular organization of the motor cortex in man. We used transcranial magnetic stimulation to induce motor evoked potentials (MEP's) in Abductor Pollicis Brevis (APB) and Biceps Brachii (BB) muscles of 10 healthy volunteers. The practicality and accuracy of magnetic stimulation to scalp sites one cm apart was increased by the application to the scalp of a flexible nylon grid with grid size of 1x1 cm. Responsive scalp sites collectively contributed to distinct but overlapping muscle representational areas for the two muscles. The topography of these motor maps along and slightly anterior to the central fissure corresponds to the homuncular configuration as described by Penfield and Boldrey in 1937.

Adult↗
PubMed1982

[Structural-functional reorganization of the brain after sequential removal of the regions of the motor cortex in cats and dogs].

It was shown in experiments on cats and dogs that the greater the mass of removed motor cortex on one side, the longer the time for restoring lost motor functions. Repeated ablations of the areas adjacent with the previously extirpated cortical zone after the restoration of motor functions, bring about the recurrence of the same disturbances. However the period of restoration after each repeated extirpation is perceptibly shorter. This means that repeated extirpations of cortical areas result in the activation of the mechanisms directed at the reorganization of the brain sensorimotor functions as a new integral system and providing for normalization of the motor functions.

Animals↗
PubMed1996

Differential relation of discharge in primary motor cortex and premotor cortex to movements versus actively maintained postures during a reaching task.

The activity of cells in primary motor cortex (MI) and dorsal premotor cortex (PMd) were compared during reaching movements in a reaction-time (RT) task, without prior instructions, which required precise control of limb posture before and after movement. MI neurons typically showed strong, directionally tuned activity prior to and during movement as well as large gradations of tonic activity while holding the limb over different targets. The directionality of their movement- and posture-related activity was generally similar. Proximal-arm muscles behaved similarly. This is consistent with a role for MI in the moment-to-moment control of motor output, including both movement and actively maintained postures, and suggests a common functional relation for MI cells to both aspects of motor behavior. In contrast, PMd cells were generally more phasic, frequently emitting only strong bursts of activity confined mainly to the behavioral reaction time before movement onset. PMd tonic activity during different postures was generally weaker than in MI, and showed a much more variable relation with their movement-related directional tuning. These results imply that the major contribution of PMd to this RT task occurred prior to the onset of movement itself, consistent with a role for PMd in the selection and planning of visually guided movements. Furthermore, the nature of the relative contribution of PMd to movement versus actively maintained postures appears to be fundamentally different from that in MI. Finally, there was a continuous gradient of changes in responses across the rostrocaudal extent of the precentral gyrus, with no abrupt transition in response properties between PMd and MI.

Animals↗
PubMed1983

Afferent connections of the lateral agranular field of the rat motor cortex.

Retrograde axonal transport techniques were used to identify the afferent connections of the lateral agranular field (AG1) of the rat frontal cortex. This cytoarchitectonically distinct cortical field forms the bulk of the primary motor cortex (MI) as defined by intracortical microstimulation studies (Donoghue and Wise, '82). Following injections of horseradish peroxidase (HRP) or wheat germ agglutinin conjugated to HRP into AG1, retrogradely labeled cells are found in the forebrain, thalamus, and brainstem. Within the cerebral cortex labeled neurons are mainly present in the first somatic sensory area (SI), the second somatic sensory area (SII), and the medial agranular field, which lies medial and rostral to AG1. In SI, labeled cells are found primarily in a cytoarchitecturally distinct region called the dysgranular field of SI. Labeled neurons are present in layers II and III, Va, and the deepest part of layer VI in this field and in SII. Labeled cells are also present in layers Va and VI of the densely granular field of SI, which is the part of SI that is strongly activated by cutaneous inputs. Commissural inputs to AG1 arise from layers II-VI of the contralateral AG1 and thalamic inputs arise from the ventrolateral, ventromedial, posterior medial, and central lateral nuclei. Additional afferent fibers originate from neurons in the basal forebrain, the ventral thalamus, the midbrain raphé nuclei, and the locus coeruleus. This combination of inputs to AG1 from somatic sensory and frontal cortical fields, thalamic motor centers, and several other subcortical areas implies that AG1 forms a subdivision of sensorimotor cortex that is important in centrally directed movements as well as those that are guided by somatic sensory feedback.

Afferent Pathways↗
PubMed2005

[The neuronal level of motor activity: determination of motor cortex excitability by TMS].

Transcranial magnetic stimulation as mapping method offers the possibility to measure aspects of motor cortex excitability painlessly and non-invasively. Using this neurophysiological tool, new insights into the effects of central-acting drugs are possible. Particularly striking seems to be the potential of this approach to gain new insights into neurobiological processes associated with neuropsychiatric diseases like schizophrenia or major depression. In combination with genetic aspects, TMS is able to bridge the gap between molecular research and clinical approach.

Antipsychotic Agents↗
PubMed2005

Behavioral and neurophysiological effects of delayed training following a small ischemic infarct in primary motor cortex of squirrel monkeys.

A focal injury within the cerebral cortex results in functional reorganization within the spared cortex through time-dependent metabolic and physiological reactions. Physiological changes are also associated with specific post-injury behavioral experiences. Knowing how these factors interact can be beneficial in planning rehabilitative intervention after a stroke. The purpose of this study was to assess the functional impact of delaying the rehabilitative behavioral experience upon movement representations within the primary motor cortex (M1) in an established nonhuman primate, ischemic infarct model. Five adult squirrel monkeys were trained on a motor-skill task prior to and 1 month after an experimental ischemic infarct was induced in M1. Movement representations of the hand were derived within M1 using standard electrophysiological procedures prior to the infarct and again one and two months after the infarct. The results of this study show that even though recovery of motor skills was similar to that of a previous study in squirrel monkeys after early training, unlike early training, delayed training did not result in maintenance of the spared hand representation within the M1 peri-infarct hand area. Instead, delaying training resulted in a large decrease in spared hand representation during the spontaneous recovery period that persisted following the delayed training. In addition, delayed training resulted in an increase of simultaneously evoked movements that are typically independent. These results indicate that post-injury behavioral experience, such as motor skill training, may modulate peri-infarct cortical plasticity in different ways in the acute versus chronic stages following stroke.

Analysis of Variance↗
PubMed1976

Disynaptic inhibition of spinal motoneurones from the motor cortex in the monkey.

1. The neuronal mechanism of disynaptic inhibition of spinal motoneurones by the corticospinal tract was investigated in Macaca irus. Surface stimulation or weak intracortical stimulation was used in order to evoke the inhibition. Intracellular records were taken from motoneurones in lumbar segments. 2. Both the disynaptic i.p.s.p.s evoked from group Ia afferents and the disynaptic i.p.s.p.s evoked from corticospinal fibres were found to be depressed by conditioning stimulation of motor axons to antagonistic muscles. Mutual facilitation of the actions from these two fibre systems occurred when nerve impulses set up in them reached the explored spinal segment synchronously. These observations led to the conclusion that disynaptic i.p.s.p.s from group Ia afferents and from the motor cortex are mediated by common interneurones. 3. No evidence either for or against projections of the same pyramidal tract cells to motoneurones of one motor nucleus and to interneurones interposed between group Ia afferents and motoneurones of an antagonistic muscle could be obtained by comparing cortical areas from which monosynaptic e.p.s.p.s and disynaptic i.p.s.p.s were evoked in the different motor nuclei. 4. The areas from which the disynaptic i.p.s.p.s were evoked in individual motoneurones appeared to be similar in size to the areas of cortical monosynaptic projections to motoneurones and showed similar degrees of overlap, indicating that the projections of pyramidal tract cells to Ia inhibitory interneurones are as extensive as to motoneurones and that they are similarly organized.

Animals↗
PubMed2002

Direct demonstration of the effects of repetitive transcranial magnetic stimulation on the excitability of the human motor cortex.

The effects of repetitive transcranial magnetic stimulation (rTMS; 20 stimuli at 5 Hz at 120% resting motor threshold intensity using a biphasic stimulus pulse) on the excitability of human motor cortex were investigated in two patients who had an electrode implanted into the cervical epidural space. The corticospinal D wave increased in amplitude with successive stimuli, and reached a maximum after three or five pulses. At this stage, the amplitude of the I waves was unchanged, but after a further 10 stimuli an additional I wave was recruited. Both effects were still evident 2 min after the end of the rTMS. The effects are compatible with a short-term increase in cortical excitability during suprathreshold rTMS.

Aged↗
PubMed1999

Corticostriatal projections from distal and proximal forelimb representations of the monkey primary motor cortex.

Corticostriatal projections from one distal and two proximal subregions in the forelimb representation of the primary motor cortex (MI) were examined in the macaque monkey. The distal and proximal subregions in the anterior bank of the central sulcus (distal and proximal-bank subregions) and the proximal subregion in the surface of the precentral gyrus (proximal-surface subregion) of the MI were identified using intracortical microstimulation. Different anterograde tracers were then injected into two of these three forelimb subregions of the MI. In the ipsilateral putamen, the distribution areas of corticostriatal fibers from the distal, proximal-bank and proximal-surface subregions were arranged from ventrolateral to dorsomedial in this order. These corticostriatal input zones were largely segregated from one another.

Animals↗
PubMed2006

Global activation of primary motor cortex during voluntary movements in man.

Unilateral voluntary movements are accompanied by robust activation of contralateral primary motor cortex (M1) in a somatotopic fashion. Occasionally, coactivation of M1 (M1-CoA) ipsilateral to the movement was described. In a study with brain tumor patients, we consistently observed additional somatotopic M1-CoAs and hypothesized that they might represent a basic feature of movement execution. To test this hypothesis, we used BOLD functional magnetic resonance imaging in healthy subjects and show that unilateral voluntary movements of the fingers or toes go along not only with contralateral M1 activation, but also with ipsilateral M1-CoA of the respective homotopic representation and bilateral M1-CoA of different heterotopic representations not directly involved in the executed movement. Moreover, bilateral M1-CoA of heterotopic representations was observed in tongue movements. All M1-CoAs respected the correct somatotopy; however, their Euclidean coordinates were shifted and resembled to those obtained for imagined movements rather than for actual movements. BOLD signal intensities and correlations to the applied hemodynamic reference function were lower in M1-CoAs as compared to the M1 activations driving the movement but did not differ between homo- and heterotopic M1-CoAs. Thus, we propose that specific unilateral voluntary movements are accompanied by a global activation of primary motor areas, reflecting an overall increase in neuronal activity and unraveling the fundamental principle of distributed processing in M1. Executive motor function may rely on a balance of inhibitory and excitatory neuronal activity, where actual movement would result from a shift towards excitation.

Adult↗
PubMed1996

Somatosensory input onto pyramidal tract neurons in rodent motor cortex.

This study was performed to determine whether pyramidal tract neurons (PTNs), the output cells of the motor cortex, are targets of direct input from the somatosensory cortex (SI). PTNs were identified by light microscope (LM) and electron microscope (EM) retrograde tract tracing techniques. For LM analysis, they were intracellularly filled to exhibit their full dendritic arbor. Axons originating from the electrophysiologically identified forelimb representation of SI were labeled by LM and EM anterograde tract tracing techniques. LM analysis of dual-labeled tissue showed that PTNs were situated to receive direct input from SI. The distribution and density of this input was predicted from the findings. EM analysis confirmed that PTNs receive direct input from SI. The input is sparse and not all PTNs appear to receive input. SI terminals do not appear to target specific segments of PTN dendrites. This corticocortical pathway may provide MI with the short latency sensory feedback which is needed to produce coordinated voluntary movements.

Amidines↗
PubMed1984

Response properties and morphological identification of neurons in the cat motor cortex.

Intracellular recordings and morphological identification of neurons using intracellular HRP staining were performed in the cat motor cortex. By thalamic ventrolateral (VL) or cerebellar nucleus stimulation, pyramidal cells in layer III, fast pyramidal tract neurons (PTNs) and stellate cells in layers II and III were activated with short latency and fast rising EPSPs, while pyramidal cells in layer II and slow PTNs showed longer latency and slow rising EPSPs. This difference may be related to activation through the deep and superficial thalamocortical projections. Although pyramidal cells in layer VI did not respond orthodromically to VL or cerebellar stimulation, some of them proved to receive the recurrent action of PTNs because of the response to stimulation of the cerebral peduncle (CP). One aspinous stellate cell in layer III was activated by CP as well as VL stimulation. This cell was supposed to be an inhibitory interneuron responsible for both recurrent and VL-evoked inhibition.

Animals↗
PubMed1989

Separation of different types of afterpotentials following penicillin-induced paroxysmal depolarization shifts of neurons in the motor cortex of the rat.

Afterpotentials of penicillin-induced paroxysmal depolarization shifts (PDS) of neurones in the motor cortex of the rat in vivo were investigated with intracellular recordings. Following the PDS, 4 different types of afterpotentials were observed: fast afterhyperpolarizations with an average duration of 600 ms, fast afterdepolarizations with an average duration of 700 ms, slow afterhyperpolarizations with an average duration of 1.9 s and slow afterdepolarizations with an average duration of 1.8 s. The fast and slow afterpotentials could occur in various combinations with the exception of a fast afterhyperpolarization followed by a slow afterdepolarization. Neurones displaying afterdepolarizations had higher resting membrane potentials than those displaying afterhyperolarizations, i.e. the polarity of the afterpotential depended on membrane potential. Experiments with intracellular Cl- injection indicated that the fast but not the slow afterpotentials are associated with an increase in membrane Cl- conductance. The slow afterhyperpolarizations are suggested to result from a calcium-dependent or a synaptically generated potassium current.

Animals↗