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At least 937 records · Page 52Linked to original sources
PubMed2004

Dopamine modulation of glutamate metabotropic receptors in conditioned reaction of sensory motor cortex neurons of the cat.

The dopamine modulation of microiontophoretic application of antagonists of glutamate metabotropic synaptic transmission was studied in the sensory motor cortex of awake cats during instrumental conditioned reflex. The substances depressed the background and intensity of evoked impulse activity of pyramidal neurons of the sensory-motor cortex and provoked significant increases in the latency of impulse reaction and corresponding conditioned movements of animals. Simultaneous application of the antagonists and dopamine (DA) eliminated their depression of the background and evoked activity of neurons and decreased the latency of the impulse reactions and movements. Similar qualitative effects were observed in experiments with simultaneous application of biccuculine and (RS)-alpha-methyl-4-carboxyphenylglycine. It is supposed that the DA modulation in the brain consists in stabilizing the background and evoked activity of cortical neurons during reduced intensity of metabotropic glutamatergic synaptic transmission. Such modulation can be important when considering some pathological disorders of glutamatergic transmission.

Animals↗
PubMedDate not supplied

Mechanisms of the formation of reactions of cat motor cortex neurons associated with the triggering of the conditioned placing reflex: a hypothesis.

The possible physiological mechanisms of the generation of reactions by neurons of the cat motor cortex during the triggering of a conditioned placing reflex are examined. It is hypothesized that neurons of the motor cortex function as a neuronal generator similar to the spinal generator of locomotion, which can be triggered through ion channels that are controlled by NMDA-type glutamate receptors. The conditions necessary for the opening of these channels under the influence of glutamate are achieved by the conditioned "arousal reaction", the neurochemical equivalent of which is an intensification of the cholinergic and noradrenergic and/or serotoninergic afferentation to the cortex.

Animals↗
PubMed2003

Prolonged peripheral nerve stimulation induces persistent changes in excitability of human motor cortex.

This study sought to determine whether prolonged peripheral nerve stimulation was effective in inducing persistent "plastic" changes in the excitability of the human motor cortex. The amplitude of the electromyographic response evoked in resting intrinsic hand muscles by focal transcranial magnetic stimulation (TMS) was taken as an index of motor cortical excitability. Twelve subjects were stimulated with each of three protocols, one of which was given on each of three separate occasions. The protocols consisted of various schedules of electrical stimulation of the radial and ulnar nerves or the motor point of the first dorsal interosseous muscle (FDI), or stimulation of FDI motor point paired with low-frequency TMS. Amplitudes of TMS-elicited motor evoked potentials (MEPs) were measured before peripheral stimulation and for 2 h after stimulation. The data from one subject were unusable. In every other subject, all three protocols induced a prolonged, significant facilitation of MEPs in at least some of the three intrinsic hand muscles used. In some instances, MEPs were not enlarged and occasionally were significantly depressed. Different protocols based on peripheral afferent stimulation can induce plastic changes in the organisation of the motor cortex that persist for at least 2 h.

Adult↗
PubMedDate not supplied

[The late excitatory responses of the motor cortex neurons in the cat to stimulation of the pyramidal tract].

Under conditions of partial suppression of GAMKA-dependent cortical inhibition in the motor cortex of anesthetized cats, a weak electrical stimulation of the pyramidal tract evoked the late slow (50-200 ms) excitatory reactions in the motor cortex neurons similar to those previously recorded under the same conditions in response to stimulation of the parietal cortex. This finding favors the proposal that the late excitatory component of the cortico-cortical response reflects the repetitive activation of cortical neurons due to excitation spread via the system of cortical recurrent excitatory collaterals.

Animals↗
PubMed2003

A ticklish question: does magnetic stimulation of the primary motor cortex give rise to an 'efference copy'?

In order to make accurate predictions about the somatosensory consequences of our own movements, an 'efference copy' of motor output appears to be used (probably in the cerebellum) as a basis for anticipating and canceling incoming information about self-produced movement. One everyday phenomenon that results from these predictive processes is that of being unable to tickle oneself. We examined whether involuntary movements induced by magnetic stimulation of (a) the motor cortex and (b) the bicep muscle, both resulting in standard stimulation of the participant's bare foot, would be perceived as ticklish. In both cases, the stimulus to the foot was rated as ticklish as when the experimenter tickled the participant's foot (using an identical stimulus). We conclude that magnetic stimulation of the motor cortex is unlikely to give rise to an efference copy of motor output.

Adult↗
PubMed2002

Motor cortex activation by transcranial magnetic stimulation in ataxia patients depends on the genetic defect.

In patients with degenerative ataxia, various abnormalities in motor cortex activation by transcranial magnetic stimulation (TMS) have been observed, including a reduction of intracortical facilitation and a lengthening of the silent period. However, the groups of patients examined in previous studies were heterogeneous, involving patients with autosomal-dominant and idiopathic cerebellar ataxia, and showing different clinical features. The aim of our present study was to investigate whether differences in motor cortex activation by TMS could be observed in genetically defined subtypes of degenerative ataxia. We examined six patients with Friedreich's ataxia, three patients with spinocerebellar ataxia (SCA) type 1, seven patients with SCA2, 12 patients with SCA3, nine patients with SCA6 and 14 healthy controls. In all subjects, motor threshold, central motor conduction time, cortical silent period after TMS, and intracortical inhibition and facilitation (as assessed by TMS using a paired pulses paradigm) were determined. Additionally, F wave amplitudes evoked by electrical peripheral nerve stimulation were measured. We found a significant reduction of intracortical facilitation in SCA2 and SCA3 patients. Furthermore, motor threshold was elevated in SCA1, central motor conduction time was lengthened in patients with Friedreich's ataxia and SCA1, and F wave amplitudes were enlarged in all the genetic subgroups except for SCA6. Silent period and intracortical inhibition did not differ between patients and controls. We conclude that changes of intracortical facilitation induced by TMS and other excitability parameters of the motor system are not a common phenomenon in degenerative ataxia, but are restricted to specific subtypes. This points to differences in the underlying pathophysiological processes in genetic subtypes of ataxia.

Adolescent↗
PubMed2006

The role of GABA(B) receptors in intracortical inhibition in the human motor cortex.

While GABA(B) receptors are thought to have an important role in mediating long interval intracortical inhibition (LICI) in the human motor cortex, the effect of a selective GABA(B) receptor agonist on this measure has not been directly tested. Nine healthy volunteers ingested either 50 mg baclofen (BAC) or placebo (PBO) in a randomized, double blind crossover design, with the second session one week later. We used transcranial magnetic stimulation to assess motor threshold, motor evoked potential (MEP) amplitude, cortical silent period (CSP) duration, short interval intracortical inhibition (SICI) and LICI before and 90 min following drug intake. There was no specific effect of drug on motor threshold, MEP amplitude or CSP duration. BAC resulted in a significant increase in LICI (P=0.002) and a significant decrease in SICI (P=0.046) while PBO had no effect. Our findings demonstrate that the enhanced GABA(B) receptor activation results in differential effects on these two measures of intracortical inhibition in the human motor cortex. The increase in LICI is likely to be a result of increased GABA(B) receptor mediated inhibitory post-synaptic potentials, while the reduction in SICI may relate to the activation of pre-synaptic GABA(B) receptors reducing GABA release.

Adult↗
PubMed1993

Efficacy of sulthiame (Ospolot) on motor partial seizure status during sleep in a patient with motor cortex epilepsy.

An 18-year-old female patient with a particular form of intractable motor cortex epilepsy, in which motor partial seizure status occurred only during sleep every night, was reported focusing on the drastic efficacy of sulthiame on the seizure status. Moreover, the present study demonstrated that single photon emission computed tomography (SPECT) and pulse oximetry examinations, both of which were performed in the ictal state, were useful for the regional diagnosis of the epileptic focus and observations of the seizure frequency, respectively. The therapeutic effect, epileptic picture and clinical examinations described here appear to be relatively rare in the literature, and therefore, this case report may be of clinical significance.

Adult↗
PubMed1996

Enhancement of human motor cortex inhibition by the dopamine receptor agonist pergolide: evidence from transcranial magnetic stimulation.

Focal transcranial magnetic stimulation was used to evaluate the effect a single oral dose (0.125 mg) of the dopamine agonist pergolide on the excitability of the motor cortex in five healthy subjects. Resting and active motor thresholds of the abductor digiti minimi muscle were unaffected. The mean duration of the cortical silent period was significantly lengthened by up to 22 ms. The cortico-cortical inhibition as studied by a paired conditioning-test stimulation (interstimulus intervals of 1-5 ms) was enhanced significantly while the cortico-cortical facilitation at longer intervals (6-15 ms) showed only an insignificant trend towards less facilitation. All effects peaked at 3 h after drug intake and were reversible after 24 h. Peripheral motor excitability as tested by the duration of the peripheral silent period and the size of the maximum M wave remained unchanged. The present data support the view that pergolide is capable of enhancing motor cortex inhibition which is known to be deficient in idiopathic Parkinson's disease.

Electromyography↗
PubMed2002

Complex modulation of human motor cortex excitability by the specific serotonin re-uptake inhibitor sertraline.

Monoamines are powerful modulators of cortical function. Serotonin has complex excitatory and inhibitory effects on animal cortex. Here, the effects of a single oral dose (100mg) of the selective serotonin re-uptake inhibitor sertraline on human motor cortex excitability were investigated in healthy subjects. Transcranial magnetic stimulation was used to test motor threshold, motor evoked potential intensity curve, cortical silent period, paired-pulse inhibition and facilitation and I-wave facilitation. Sertraline resulted in a steeper intensity curve and in depressed paired-pulse facilitation (PPF). All other measures and spinal and neuromuscular excitability remained unaffected. The steeper intensity curve points to an increased excitability of the cortico-spinal neurone, while the depressed PPF suggests an enhanced control of the cortico-spinal neurone by inhibitory interneurones. These features may improve the signal-to-noise ratio of output cells in human motor cortex.

Adult↗
PubMed1988

Projection on the motor cortex of thalamic neurons with pallidal input in the monkey.

The cortical projection areas of thalamic neurons with basal ganglia and/or cerebellar inputs were studied electrophysiologically in unanesthetized monkeys. Thalamic neurons which receive inhibition from the pallidum were found to project to the motor cortex (area 4) as well as to premotor cortex. The neurons with pallidal input and motor cortical projection were located mainly in VLo. This result indicates that the basal ganglia innervate the motor cortex through the thalamus. Thus the basal ganglia can modify the cortical output for controlling movements directly through this pathway as compared with its influence through the prefrontal and premotor cortices.

Action Potentials↗
PubMed1997

Multiple divisions of macaque precentral motor cortex identified with neurofilament antibody SMI-32.

In brain sections stained with monoclonal antibody SMI-32, which recognizes non-phosphorylated neurofilament protein, we distinguished separate caudal, intermediate, and rostral subdivisions of gigantocellular precentral cortex (areas 4c, 4i, and 4r) in macaque monkeys. The divisions form bands extending mediolaterally across the major body-region representations of the primary motor cortex (M1). These observations provide additional evidence that primary motor cortex is not a single, structurally homogeneous cortical area.

Animals↗
PubMed1996

Use-dependent alterations of movement representations in primary motor cortex of adult squirrel monkeys.

This study was undertaken to document plastic changes in the functional topography of primary motor cortex (M1) that are generated in motor skill learning in the normal, intact primate. Intracortical microstimulation mapping techniques were used to derive detailed maps of the representation of movements in the distal forelimb zone of M1 of squirrel monkeys, before and after behavioral training on two different tasks that differentially encouraged specific sets of forelimb movements. After training on a small-object retrieval task, which required skilled use of the digits, their evoked-movement digit representations expanded, whereas their evoked-movement wrist/forearm representational zones contracted. These changes were progressive and reversible. In a second motor skill exercise, a monkey pronated and supinated the forearm in a key (eyebolt)-turning task. In this case, the representation of the forearm expanded, whereas the digit representational zones contracted. These results show that M1 is alterable by use throughout the life of an animal. These studies also revealed that after digit training there was an areal expansion of dual-response representations, that is, cortical sectors over which stimulation produced movements about two or more joints. Movement combinations that were used more frequently after training were selectively magnified in their cortical representations. This close correspondence between changes in behavioral performance and electrophysiologically defined motor representations indicates that a neurophysiological correlate of a motor skill resides in M1 for at least several days after acquisition. The finding that cocontracting muscles in the behavior come to be represented together in the cortex argues that, as in sensory cortices, temporal correlations drive emergent changes in distributed motor cortex representations.

Animals↗
PubMed2003

Functional connectivity revealed by single-photon emission computed tomography (SPECT) during repetitive transcranial magnetic stimulation (rTMS) of the motor cortex.

OBJECTIVE: In the present study, we studied effects of 1 Hz repetitive transcranial magnetic stimulation (rTMS) over the left primary motor cortex (M1) on regional cerebral blood flow (rCBF) using single-photon emission computed tomography (SPECT). METHODS: SPECT measurements were carried out under two experimental conditions: real and sham stimulation. In sham stimulation, to exclude other components besides currents in the brain in rTMS, we applied sound and electrical stimulation to the skin of the head. 99mTc-ethyl cysteinate dimer was injected during the real or sham stimulation. Images were analyzed with the statistical parametric mapping software (SPM99). Relative differences in adjusted rCBF between two conditions were determined by a voxel-by-voxel paired t test. RESULTS: 1 Hz rTMS at an intensity of 1.1 x active motor threshold evoked increase of rCBF in the contralateral (right) cerebellar hemisphere. Reduction of rCBF was observed in the contralateral M1, superior parietal lobule (most probably corresponding to PE area in the monkey) (Rizzolatti G, Luppino G, Matelli M. Electroenceph clin Neurophysiol 1998;106:283-296), inferior parietal lobule (PF area in the monkey (Rizzolatti et al., 1998)), dorsal and ventral premotor areas (dPM, vPM) and supplementary motor area (SMA). CONCLUSIONS: Increase of rCBF in the contralateral cerebellum must reflect facilitatory connection between the motor cortex and contralateral cerebellum. Reduced rCBF in the contralateral M1 may be produced by transcallosal inhibitory effect of the left motor cortical activation. CBF decrease in the right PM, SMA and parietal cortex may reflect some secondary effects. Low frequency rTMS at an intensity of around threshold for active muscles can evoke rCBF changes. SIGNIFICANCE: We demonstrated that rCBF changes could be elicited even by low frequency rTMS at such a low intensity as the threshold for an active muscle. Combination of rTMS and SPECT is one of powerful tools to study interareal connection within the human brain.

Adult↗
PubMed2005

Response-specific sources of dual-task interference in human pre-motor cortex.

It is difficult to perform two tasks at the same time. Such performance limitations are exemplified by the psychological refractory period (PRP): when participants make distinct motor responses to two stimuli presented in rapid succession, the response to the second stimulus is increasingly slowed as the time interval between the two stimuli is decreased. This impairment is thought to reflect a central limitation in selecting the appropriate response to each stimulus, but not in perceptually encoding the stimuli. In the present study, it was sought to determine which brain regions are specifically involved in response selection under dual-task conditions by contrasting fMRI brain activity measured from a response selection manipulation that increased dual-task costs, with brain activity measured from an equally demanding manipulation that affected perceptual visibility. While a number of parieto-frontal areas involved in response selection were activated by both dual-task manipulations, the dorsal pre-motor cortex, and to a lesser extent the inferior frontal cortex, were specifically engaged by the response selection manipulation. These results suggest that the pre-motor cortex is an important neural locus of response selection limitation under dual-task situations.

Adult↗
PubMed2002

Lewy bodies in Betz cells of the motor cortex in a patient with Parkinson's disease.

Lewy bodies (LBs) were observed in the giant pyramidal cells of Betz in the motor cortex of a patient with Parkinson's disease (PD) of 8-year duration. The patient had shown typical clinical features of PD. No dementia or pyramidal tract signs had been observed. The LBs, found in 8 of 747 Betz cells counted (1.1%), appeared as homogeneous or laminated, spherical inclusions with a clear surrounding halo and were strongly immunoreactive for alpha-synuclein. To our knowledge, this is the first demonstration of LBs in Betz cells. Considering the significant loss of neurons in the predilection sites for LBs, it is possible that in this patient, the motor cortex was also involved in the disease process of PD.

Humans↗
PubMed1992

Functional properties of single neurons in the face primary motor cortex of the primate. III. Relations with different directions of trained tongue protrusion.

1. In previous papers we presented evidence pointing to an important role for face motor cortex in the control of tongue movements. Intracortical microstimulation (ICMS) at many sites within face motor cortex evoked different types of tongue movement, and many neurons at these "tongue-MI" sites received intraoral mechanosensitive afferent input, and their activity was related to a tongue-protrusion task performed by a monkey. In view of the synergistic action of the various tongue muscles during tongue movement, we hypothesized that these different tongue-MI sites are recruited to effect the appropriate change in tongue shape and position during a tongue-protrusion movement. A prediction from this hypothesis is that variations in the direction of a tongue-protrusion movement should be associated with variations in the activities within the different tongue-MI efferent zones. Differences in efferent-zone activity should be reflected in differences in the firing rates of neurons that are located at these tongue-MI sites. 2. We trained two monkeys to perform a tongue-protrusion task at each of three directions. The tongue-protrusion task transducer was positioned at 0 degrees (Ts), 30 degrees to the left (Tlt), or 30 degrees to the right (Trt) from the midsagittal plane; the latter two positions were termed asymmetric tongue-protrusion task positions. Single neurons were recorded from tongue-MI during trials of tongue-protrusion task at each of two or three of the above positions. Some of the neurons were also studied during a biting task. In addition, neurons were tested for possible mechanosensitive afferent input. 3. Of the 66 neurons studied, 31 (45%) exhibited directional relations; that is, the change in firing rate between the pretrial period (PTP) and the task period for the tongue-protrusion task was significantly different for each neuron depending on the direction in which the activity of the neuron was studied. 4. The "directional" neurons exhibited a single preferred direction of firing in that the mean firing rate during one direction of tongue-protrusion task was significantly greater than for any other direction. Of the 20 neurons studied at all three directions of tongue-protrusion task, the mean firing rate of each of 18 was highest at one of the asymmetric positions, and 12 of these 18 neurons exhibited a monotonic decrease in absolute firing frequency from one asymmetric task direction to the other. 5. Thirteen of the neurons were also studied while the monkey performed the biting task. Most tongue-MI directional neurons were not related to the biting task.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗