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At least 649 records · Page 36Linked to original sources
PubMed1999

Inhibition in the human motor cortex is reduced just before a voluntary contraction.

OBJECTIVE: To examine inhibition in the human motor cortex before and during voluntary movements. METHODS: The balance between the excitation and inhibition of corticospinal neurons in the human motor cortex was tested by conditioning the motor evoked potentials (MEP) evoked in forearm muscles by transcranial magnetic stimulation with a preceding subthreshold stimulus delivered through the same coil. RESULTS: When normal individuals (n = 9) made a tonic wrist extension, inhibition of the forearm extensor MEP decreased, whereas that of the forearm flexors was unchanged. When these individuals made a tonic wrist flexion, inhibition of the forearm flexor MEP diminished, whereas that of the forearm extensors was unchanged. When normal individuals (n = 10) made a phasic wrist extension in response to an auditory signal, inhibition of the extensor MEP began to decline about 95 msec before the onset of the agonist EMG activity. CONCLUSIONS: The changes in balance of excitation and inhibition of corticospinal neurons associated with a voluntary movement precede the movement and are directed at the corticospinal neurons projecting to the agonists. These changes may help to select the population of cortical neurons responsible for the movement.

Action Potentials↗
PubMed2004

Real time fMRI: a tool for the routine presurgical localisation of the motor cortex.

In patients with brain lesions adjacent to the central area, exact preoperative knowledge of the spatial relation of the tumour to the motor cortex is of major importance. Many studies have shown that functional magnetic resonance imaging (fMRI) is a reliable tool to identify the motor cortex. However, fMRI data acquisition and data processing are time-consuming procedures, and this prevents general routine clinical application. We report a new application of real time fMRI that allows immediate access to fMRI results by automatic on-line data processing. Prior to surgery we examined ten patients with a brain tumour adjacent to the central area. Three measurements were performed at a 1.5-T Magnetom Vision Scanner (Siemens, Forchheim, Germany) on seven patients and at a 1.5-T Intera Scanner (Philips, Best, The Netherlands) on three patients using a sequential finger-tapping paradigm for motor cortex activation versus at rest condition. Blood oxygen level-dependant (BOLD) images were acquired using a multislice EPI sequence (16 slices, TE 60, TR 6000, FOV 210x210, matrix 64x64). The central sulcus of the left hemisphere could be clearly identified by a maximum of cortical activity after finger tapping of the right hand in all investigated patients. In eight of ten patients the right central sulcus was localised by a signal maximum, whereas in two patients the central sulcus could not be identified due to a hemiparesis in one and strong motion artefacts in the second patient. Finger tapping with one side versus rest condition seems to result in more motion artefacts, while finger tapping of the right versus the left hand yielded the strongest signal in the central area. Real time fMRI is a quick and reliable method to identify the central sulcus and has the potential to become a clinical tool to assess patients non-invasively before neurosurgical treatment.

Adult↗
PubMed2004

Treatment-induced neuroplasticity following focal injury to the motor cortex.

The impairment and functional limitation associated with damage to the cerebral motor cortex is often severely disabling and can lead to extensive rehabilitation. Unfortunately, much of this rehabilitation intervention lacks a solid foundation of empirically derived evidence of its efficacy. Moreover, the continuing knowledge explosion in healthcare necessitates the need to stay abreast of ever-changing developments in rehabilitation. This paper introduces the reader to introductory neuroplasticity concepts and outlines the current knowledge on neuroplastic changes in the motor cortex, which are driven by rehabilitation. Furthermore, this paper discusses neuroplasticity concepts that can serve as a theoretical foundation behind treatment intervention.

Animals↗
PubMed2006

[Inhibitory reactions of the motor cortex neurons in the triggering of conditioned reflex organization in cats].

The neuronal impulse reactions of the motor cortex neurons (field 4) which are involved in the reflex realization were studied on the awakening cats trained to perform conditioned movement after the influence of two stimuli (the preliminary and the conditional). Slow cortex potential in vertex was registered simultaneously. It was established that before the response to the triggering signal (interstimuli period) high amplitude negative shift in the slow cortex potential is present. At the same time we registered inhibition of neuron activity which led to excitative reactions represented as potent impulses. The obtained results allow us to suggest a relationship between the development of negativeness and inhibition of motor cortex neurons during preparation to the movement.

Action Potentials↗
PubMed1977

[Inhibition in the senso-motor cortex of cats].

The responses of 340 neurons of the sensory-motor cortex to electrocutaneous stimulation of the extremities were studied in 3-30 days old kittens. Extracellular recording of 9.4% cells in 3-10 day old animals and 17.1% cells in 21-30 days old animals showed a silent period following the excitatory component of the response. Intracellular and quasi-intracellular recording revealed the presence of postsynaptic inhibition during this period. As a rule the IPSPs which followed the initial excitatory component were 250-380 ms long, being considerably longer than similar IPSPs in the sensory-motor cortex of adult cats. IPSP amplitude usually did not exceed 5 mV.

Animals↗
PubMed2004

Subthreshold rTMS over pre-motor cortex has no effect on tics in patients with Gilles de la Tourette syndrome.

OBJECTIVE: A previous study showed no effect of 1Hz repetitive transcranial magnetic stimulation (rTMS) on tics in Gilles de la Tourette Syndrome (GTS). We modified the rTMS protocol in order to investigate some of the possible methodological reasons for the negative outcome in that study. METHODS: In a single blinded placebo-controlled cross-over study in five GTS patients without obsessive compulsive disorder we probed whether longer trains (1800 stimuli) of 1 Hz pre-motor cortex rTMS at 80% of active motor threshold and application to both hemispheres can improve tics in GTS. This was measured with the Yale Global Tic severity rating scale, the MOVES self-rating scale and video analysis. RESULTS: We found no significant effect of either left pre-motor cortex stimulation alone, or left pre-motor followed by right pre-motor cortex stimulation. CONCLUSIONS: These results suggest that the rTMS protocol used in this study is not useful for the treatment of tics in GTS. SIGNIFICANCE: rTMS protocols need to be modified substantially in order to explore their potential for the treatment of tics in GTS.

Adult↗
PubMed2006

Stimulation of the motor cortex for disabling essential tremor.

OBJECTIVE: To examine the safety and efficacy of targeted stimulation of the motor cortex as a treatment for essential tremor (ET). PATIENTS AND METHODS: At the University of Kansas Medical Center, two patients with essential tremor received stimulation of the (contralateral) motor cortex using an investigational implantable pulse generator (IPG). Patients were evaluated with the Fahn Tolosa Marin tremor rating scale (TRS) at baseline, 1 week and 4 weeks after surgery, both with stimulation turned on and turned off. Both patients also received neuropsychological assessments at baseline and again after surgery. RESULTS: Patient 1 was a 75-year-old male with tremor for 20 years. His baseline total TRS score was 61 and his TRS 1 month after surgery was 57. His IPG was set at 30 Hz, 3 mA and 250 micros pulse width. Patient 2 was a 60-year-old male with tremor for over 10 years. His baseline total TRS was 47 and it was 43, 1 month after surgery. His IPG was set at 50 Hz, 5 mA and 250 micros pulse width. There were no adverse effects. CONCLUSION: Cortical stimulation of the primary hand motor cortex contralateral to the dominant hand was ineffective for the treatment of ET with the stimulation parameters used in this study. Future research examining other stimulation parameters is necessary to determine if there is a role for cortical stimulation in the treatment of ET.

Aged↗
PubMed1973

Motor cortex reflexes associated with learned movement.

In primates, sensory input can generate reflex motor cortex output in association with learned movement when the sensory input has a strong and direct connection to the motor cortex-for example, when a stimulus calling for repositioning of the hand consists of a perturbation of hand position. This finding supports the proposal that neurons of primate motor cortex may function in a transcortical servo-loop.

Action Potentials↗
PubMed2003

Interactions between inhibitory and excitatory circuits in the human motor cortex.

Cortical activity depends on the balance between excitatory and inhibitory influences. Several different excitatory and inhibitory systems in the human motor cortex can be tested by transcranial magnetic stimulation (TMS). While considerable information is known about these different inhibitory and excitatory phenomena individually, how they are related to each other and how they interact is not well understood. Several recent studies have investigated the interactions between some of these circuits by applying them together. It has been found that short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) are mediated by different circuits. LICI appears to inhibit SICI, which may occur through presynaptic GABA(B) receptors. Interhemispheric inhibition elicited by stimulation of the contralateral motor cortex also inhibits SICI and may share inhibitory mechanisms with LICI. Long-interval afferent inhibition induced by median nerve stimulation inhibits LICI but does not interact with SICI. Based on these results, a model of interactions between different inhibitory systems that can be tested and refined in the future is proposed. Further studies of the interaction between different cortical inhibitory and excitatory circuits should improve our understanding of the functional organization of the motor cortex and allow better interpretation of abnormal findings in disease states. It may also be developed into a new way of studying the pathophysiology of diseases and the effects of intervention.

Electric Stimulation↗
PubMed2001

Oscillatory interaction between human motor cortex and trunk muscles during isometric contraction.

We investigated oscillatory interaction between magnetoencephalographic signals of the human motor cortex and surface electromyogram from the paraspinal (PS) and abdominal (ABD) muscles. The results were compared with data obtained during contraction of the first dorsal interosseus (FDI) and tibialis anterior (TA) muscles. Significant coherence at 15-35 Hz was observed for both PS and ABD muscles in all subjects but the coherence was weak compared with that for FDI and TA. The cortical sources for both the PS and the ABD coherences were located in the motor cortex between the source areas for the FDI and TA coherences, thereby agreeing with the classical trunk area of the motor homunculus previously determined by invasive studies. The sources were strictly contralateral for PS but bilateral for ABD contractions. Our results indicate that during isometric contractions descending motor commands are modulated by cortical oscillations for both limb and trunk muscles, although the modulation is weaker and may be bilateral for trunk muscles.

Abdominal Muscles↗
PubMed1986

Regional differences in evoked response latencies in the cat motor cortex (area 4 gamma).

The latencies of responses evoked in the cat motor cortex (area 4 gamma) on contralateral forelimb nerve stimulation were measured. In the caudolateral part, the latencies were 4-5 ms on ulnar and superficial radial nerve stimulation. Further, rostromedially the response latencies were longer, 7-9 ms. The latency-to-peak of the evoked responses was also measured and showed a parallel increase. In many cases, inflexions could be observed on the rising phase of the evoked potential, indicating that it consisted of several components. In most experiments, four components (I-IV) were observed. Their mean latencies were 4.3, 6.0, 7.2 and 8.5 ms, respectively. The early components were largest in the caudolateral part of area 4 gamma and decreased when recording further rostromedially such that, in the anterior sigmoid gyrus, usually only component IV could be recorded. The findings suggest that the cat motor cortex is functionally divided into regions which can be identified by their peripheral input latencies.

Animals↗
PubMed1997

Corticosubthalamic input zones from forelimb representations of the dorsal and ventral divisions of the premotor cortex in the macaque monkey: comparison with the input zones from the primary motor cortex and the supplementary motor area.

Employing double anterograde axonal tracing in combination with intracortical microstimulation, we examined the distribution patterns of corticosubthalamic inputs from forelimb representations of the dorsal (PMd) and ventral (PMv) divisions of the premotor cortex in the macaque monkey. The inputs from the PMd and PMv were distributed mainly in the medial aspect of the subthalamic nucleus (STN), in which their distribution areas overlapped each other. By the same experimental approach, we further compared corticosubthalamic input zones from the PMd/PMv with those from the primary motor cortex (MI) and the supplementary motor area (SMA). The input zones from the PMd/PMv and SMA largely overlapped in the medial aspect of the STN, whereas the input zones from the PMd/PMv and MI were virtually segregated mediolaterally in the STN.

Animals↗
PubMedDate not supplied

[NMDA-dependent and NMDA-independent neuronal processes in the cat motor cortex, disinhibited by bicuculline, during forepaw placement conditioning].

Neuronal activity associated with a conditioned forepaw placing reaction was recorded in the cat's motor cortex locally disinhibited by bicuculline spontaneously diffused from the recording pipette. Electrical stimulation of the parieral cortex (area 5) with 3-5 pulses was used as a conditioned stimulus. In both naive and trained cats, adding of APV (NMDA receptor blocker) led to disappearance of the late (30-120 ms) secondary excitatory responses from the pattern of the neuronal reaction to the parietal stimulation recorded in the motor cortex. At the same time, the APV administration did not change the excitatory reactions (recorded, predominantly, in the deep cortical layers) time-locked to the execution of the conditioned movement. The conditioning resulted in a statistically significant increase in the amplitude and duration of the late secondary responses as well as in a shortening of their latency. In some cases (after a long period of training), the late secondary responses to the conditioned stimulus transformed into paroxysmal epileptiform bursts. A hypothesis is discussed that the increase in synaptic strength of the backward horizontal collaterals of layer-II/III pyramidal neurons is responsible for the learning-related changes in the neuronal reactions in the disinhibited motor cortex.

Animals↗
PubMed1984

Effects of lateralized reaching and cerebellar stimulation on unit activity of motor cortex and caudate nucleus in rats.

Rats trained to reach into a narrow tubular feeder for food were implanted with bipolar stimulation electrodes in the dentate nucleus (DNT) ipsilateral to the preferred forepaw. Unit activity was recorded in freely moving animals (N = 15) with capillary microelectrodes inserted with a head-mounted microdrive into the contralateral motor cortex and caudate nucleus. Single-pulse stimulation of the DNT, subthreshold for eliciting overt movement and for interfering with reaching, evoked in both structures short-lasting excitatory responses sometimes preceded by brief inhibition. Reach-triggered stimulation changed the perireach histograms of the motor cortex neurons (N = 46) not only by interference with the movement-related and stimulation-elicited activities in the poststimulus interval but also considerably prolonged the prereach excitation. The perireach histograms of caudate neurons (N = 50) were not changed by the reach-triggered DNT stimulation in the prereach or in the poststimulus interval, probably because the movement-related activity overrode the electrical perturbation. The results indicated that the impairment of reaching caused by DNT stimulation was due to disorganization of the neuronal activity patterns in the motor cortex rather than in the caudate nucleus. The earlier onset of movement-related excitation in the motor cortex during stimulus-triggering reaching reflects attempts to cope with the disturbance by predictive reorganization of the motor discharge.

Animals↗
PubMed1994

Akinesia in Parkinson's disease. II. Effects of subthreshold repetitive transcranial motor cortex stimulation.

We studied the effects of repetitive transcranial stimulation of the motor cortex (rTMS) on choice reaction time (cRT), movement time (MT), and error rate (ER) in a serial reaction-time task in six medicated patients with Parkinson's disease (PD) and 10 age-matched normal controls. In normal subjects, subthreshold 5-Hz rTMS did not significantly change cRT, slightly shortened MT, but increased ER. In the patients, rTMS significantly shortened cRT and MT without affecting ER. These effects did not impair procedural learning. Performance on a grooved peg-board test was improved by rTMS in the same PD patients, especially when they were off medications, but worsened in the normal subjects. Repetitive, subthreshold motor cortex stimulation can improve performance in patients with PD and could be useful therapeutically.

Aged↗
PubMed1998

Rett syndrome, EEG and the motor cortex as a model for better understanding of attention deficit hyperactivity disorder (ADHD).

EEG data in Rett syndrome (RS) are quite often characterized by spikes over the central region (especially in sleep). Furthermore, there has been a recent observation of a prominent and peculiar theta (4-6/s) rhythm over the central region and vicinity. In view of the clinical phenomena of RS, it is pointed out that clinical and electrical findings are based upon hyperexcitability of the motor cortex (or a state of motor cortex dyscontrol). States of dyscontrol (disinhibition) are caused by deficits in higher cortical functions. It is reasonable to assume a primary dysfunction for the frontal lobe which is also smaller in size than other cerebral regions. The behavioral (motor) disturbance in RS can be easily explained as the expression of disturbed prefrontal/premotor function with special effect on the "syntax of action". It is further theorized that such a state of fronto-motor cortex uncoupling may also exist in attention deficit hyperkinetic disorder (ADHD) even though there is hardly any structural CNS impairment in that condition. A presumed "lazy frontal lobe" is likely to react favorably to the stimulation provided by methylphenidate (a therapeutic effect which should not be viewed as paradoxical).

Attention Deficit Disorder with Hyperactivity↗
PubMed2021

Comparative cellular analysis of motor cortex in human, marmoset and mouse.

The primary motor cortex (M1) is essential for voluntary fine-motor control and is functionally conserved across mammals1. Here, using high-throughput transcriptomic and epigenomic profiling of more than 450,000 single nuclei in humans, marmoset monkeys and mice, we demonstrate a broadly conserved cellular makeup of this region, with similarities that mirror evolutionary distance and are consistent between the transcriptome and epigenome. The core conserved molecular identities of neuronal and non-neuronal cell types allow us to generate a cross-species consensus classification of cell types, and to infer conserved properties of cell types across species. Despite the overall conservation, however, many species-dependent specializations are apparent, including differences in cell-type proportions, gene expression, DNA methylation and chromatin state. Few cell-type marker genes are conserved across species, revealing a short list of candidate genes and regulatory mechanisms that are responsible for conserved features of homologous cell types, such as the GABAergic chandelier cells. This consensus transcriptomic classification allows us to use patch-seq (a combination of whole-cell patch-clamp recordings, RNA sequencing and morphological characterization) to identify corticospinal Betz cells from layer 5 in non-human primates and humans, and to characterize their highly specialized physiology and anatomy. These findings highlight the robust molecular underpinnings of cell-type diversity in M1 across mammals, and point to the genes and regulatory pathways responsible for the functional identity of cell types and their species-specific adaptations.

Animals↗