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At least 1,099 records · Page 61Linked to original sources
PubMed2001

Right lateralized motor cortex activation during volitional blinking.

Using H2 15O positron emission tomography in 6 healthy volunteers, we found that self-initiated and externally cued blinking activated the right primary motor cortex and supplementary motor area (SMA). The left dorsolateral prefrontal cortex (DLPFC) and the rostral SMA showed greater activation during the self-initiated task compared to the externally cued task. This study confirms the hypothesis of right hemispheric lateralization of volitional blinking derived from observations in stroke patients. Furthermore, it underscores the role of DLPFC and rostral SMA in self-initiated movements, which has been found in similar experiments with hand movements.

Aged↗
PubMed2004

Transcranial magnetic stimulation of the human motor cortex influences the neuronal activity of subthalamic nucleus.

The critical role of the subthalamic nucleus (STN) in the control of movement and parkinsonian symptoms is well established. Research in animals suggests that the cerebral cortex plays an important role in regulating the activity of the STN but this control is not known in humans. The most extensive cortical innervation of the STN originates from motor areas. Here, we used transcranial magnetic stimulation (TMS) during intraoperative single-unit recordings from STN, in six patients with Parkinson's disease (PD) undergoing implantation of deep brain stimulators, to determine whether TMS of the motor cortex (MC) modulates the activity of STN and to investigate in vivo the functional organization of the corticosubthalamic circuit in the human brain. Single-pulse TMS of the MC induced an excitation in 74.9% of neurons investigated. This activation was followed by a long-lasting inhibition of the STN neuronal activity that did not correlate with PD severity. Responsive neurons to TMS of the hand area of motor cortex were located mainly in the lateral and dorsal region of the subthalamus while unresponsive cells had a prevalently medial distribution. This is the first report of TMS-induced modulation of STN neuronal activity in humans. These findings open up new avenues for in vivo studies of corticosubthalamic interactions in human brain and PD.

Action Potentials↗
PubMed2004

Effects of citalopram on the excitability of the human motor cortex: a paired magnetic stimulation study.

Several recent reports suggest the possibility of monitoring pharmacological effects on brain excitability through transcranial magnetic stimulation (TMS). Different drugs have been studied using paired magnetic stimulation in normal subjects and patients. In particular, it has been suggested that antidepressant drugs may have an appreciable effect on motor excitability. The aim of the present study was to investigate motor area excitability in normal subjects after oral administration of a single dose of citalopram, a selective serotonin reuptake inhibitor (SSRI) antidepressant. Motor cortex excitability was studied by single and paired transcranial magnetic stimulation before and 2.5 and 36 (t1/2=36 h) h after oral administration of 30 mg of citalopram. Cortical excitability was measured using different transcranial magnetic stimulation parameters: motor threshold (MT), motor-evoked potential (MEP) amplitude and latency, motor recruitment, duration of cortical silent period (CSP), intracortical inhibition and intracortical facilitation. Spinal excitability and peripheral nerve conduction were measured by F response and M wave. Temporary but significant increases in motor threshold, motor-evoked potentials, silent period and intracortical inhibition were observed 2.5 h after drug administration, without any significant changes in motor-evoked potential amplitude and latency and spinal excitability parameters. Our findings suggest that a single oral dose of citalopram can induce significant but transitory suppression of motor cortex excitability in normal subjects.

Administration, Oral↗
PubMed2006

Motor cortex reorganisation in Parkinson's disease.

Transcranial magnetic stimulation mapping of the motor cortical projection to the hand was performed in a group of patients with Parkinson's disease (PD) of variable duration to determine whether there is evidence of cortical reorganisation. Map shifts were found in the majority of PD cases (12/15), in untreated early cases as well as treated cases of longer duration, and there was a correlation between inter-side difference in the severity of PD symptoms (Unified Parkinson's Disease Rating Scale) and interhemispheric map displacement (r=0.60; P=0.018). These findings indicate that there is reorganisation of the corticomotor representation of the hand in PD, even at a relatively early stage of the disease, and suggest a dynamic process of reorganisation in the motor cortex due to an increase in the pallidal inhibitory inputs to the thalamo-cortical projections.

Aged↗
PubMed1993

Autoradiographic distribution of binding sites for the non-NMDA receptor antagonist [3H]CNQX in human motor cortex, brainstem and spinal cord.

The distribution of non-NMDA receptors in the normal human motor cortex, brainstem and spinal cord has been investigated using [3H]CNQX. In the motor and premotor cortex, specific [3H]CNQX binding was present in all cortical laminae with the highest density of binding sites in laminae I, II and the upper part of III. In the normal brainstem, non-NMDA receptors labelled by [3H]CNQX had a heterogeneous distribution. Brainstem motor nuclei subserving eye movements, which tend to be spared in motor neuron disease (MND), had a higher density of [3H]CNQX binding sites compared to other cranial nerve motor nuclei (VII, X, XII) which tend to be affected. Specific [3H]CNQX binding was present throughout the spinal grey matter, the greatest density of binding being found in the substantia gelatinosa. Excitotoxicity at non-NMDA receptors has been implicated in chronic neurodegenerative diseases such as motor neuron disease. This study suggests that the density of non-NMDA receptors, labelled by [3H]CNQX, does not account for selective vulnerability of motor neurons in this disorder.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2002

Neurofibrillary tangles in the primary motor cortex in Guamanian amyotrophic lateral sclerosis/parkinsonism-dementia complex.

The amyotrophic lateral sclerosis/parkinsonism-dementia complex is a chronic neurodegenerative disorder with high prevalence among the native Chamorro population of Guam. The cortical pathology of the disease is characterized by the widespread occurrence of cortical neurofibrillary tangles that exhibit a specific laminar and regional distribution different from that seen in Alzheimer's disease (AD). In spite of the major motor symptomatology, the degree to which the primary motor cortex is affected in this disease has not been investigated in detail. We report here that the primary motor cortex in Guamanian cases contains high numbers of neurofibrillary tangles, contrasting sharply with the situation in AD and in non-Chamorro cases of amyotrophic lateral sclerosis. Furthermore, the cases with predominant parkinsonism-dementia are more severely affected than amyotrophic lateral sclerosis cases. These data suggest that the regional and cellular pathology of Guamanian cases differs radically from that commonly observed in neurodegenerative diseases outside Guam and point to the existence of subgroups in the spectrum of clinical manifestations seen in Guamanian patients.

Aged↗
PubMed1995

Postnatal development of the human primary motor cortex: a quantitative cytoarchitectonic analysis.

The postnatal development of the human primary motor cortex (area 4) was analyzed in 54 individuals ranging in age from birth to 90 years. Three parameters defining major cytoarchitectonic features (areal fraction, numerical density and mean area of cells) were measured in vertical columns extending from the pial surface to the border between cortex and underlying white matter. The data were compiled in profile curves that reveal or more detailed laminar pattern than the classical cytoarchitectonic descriptions. The most pronounced decreases in numerical density and areal fraction of Nissl-stained cells profiles during early postnatal ontogeny are observed in layer II. A clearly delineable layer IV, which is still recognizable in the newborn, disappears gradually during the first postnatal months. Although the width of the cortex as a whole increases during this period, layer V, the main source of pyramidal tract fibers, is the only lamina that also increases in relative thickness. The other layers remain stable or become relatively thinner. These results reveal specific laminar growth processes in area 4, which take place in parallel with the functional maturation of the cortical motor system.

Adolescent↗
PubMed2002

Cortical spreading depression and involvement of the motor cortex, auditory cortex, and cerebellum in eyeblink classical conditioning of the rabbit.

The interrelationships of cerebellar and cerebral neural circuits in the eyeblink paradigm were explored with the controlled application of cortical spreading depression (CSD) and lidocaine in the New Zealand albino rabbit. The initial research focus was directed toward the involvement of the motor cortex in the conditioned eyeblink response. However, CSD timing and triangulation results indicate that other areas in the cerebral cortex, particularly the auditory cortex (acoustic conditioned stimulus), appear to be critical for the CSD effect on the eyeblink response. In summary: (1) CSD can be elicited, monitored, and timed and its side effects controlled in 97% of awake rabbits in the right and/or left cerebral hemisphere(s) during eyeblink conditioning. (2) The motor cortex appears to play little or no part in classical conditioning of the eyeblink in the rabbit in the delay paradigm. (3) Inactivating the auditory cortex with CSD or lidocaine temporarily impairs the conditioned response during the first 5 to 15 days of training, but has little effect past that point.

Animals↗
PubMed1997

Coherent oscillations in monkey motor cortex and hand muscle EMG show task-dependent modulation.

1. Recordings were made of local field potential (slow waves) and pyramidal tract neurone (PTN) discharge from pairs of sites separated by a horizontal distance of up to 1.5 mm in the primary motor cortex of two conscious macaque monkeys performing a precision grip task. 2. In both monkeys, the slow wave recordings showed bursts of oscillations in the 20-30 Hz range. Spectral analysis revealed that the oscillations were coherent between the two simultaneously recorded cortical sites. In the monkey from which most data were recorded, the mean frequency of peak coherence was 23.4 Hz. 3. Coherence in this frequency range was also seen between cortical slow wave recordings and rectified EMG of hand and forearm muscles active during the task, and between pairs of rectified EMGs. 4. The dynamics of the coherence were investigated by analysing short, quasi-stationary data segments aligned relative to task performance. This revealed that the 20-30 Hz coherent oscillations were present mainly during the hold phase of the precision grip task. 5. The spikes of identified PTNs were used to compile spike-triggered averages of the slow wave recordings. Oscillations were seen in 11/17 averages of the slow wave recorded on the same electrode as the triggering spike, and 11/17 averages of the slow wave recorded on the distant electrode. The mean period of these oscillations was 45.8 ms. 6. It is concluded that oscillations in the range 20-30 Hz are present in monkey motor cortex, are coherent between spatially separated cortical sites, and encompass the pyramidal tract output neurones. They are discernable in the EMG of active muscles, and show a consistent task-dependent modulation.

Animals↗
PubMed1991

A fractal analysis of pyramidal neurons in mammalian motor cortex.

Pyramidal neurons in the mammalian cerebral cortex can be described by a fractal dimension (Mandelbrot, 1982), which is an objective, quantitative measure of the complexity of their soma/dendritic borders. In the cat, the fractal dimensions of lamina V cells, which include pyramidal tract neurons (PTN), indicate that these cells are more complex than other pyramidal neurons (PN) in the same region of motor cortex. The lamina V cells of the cat are also more complex than those in motor cortex of the monkey. Moreover, lamina III neurons in the monkey are more complex than monkey lamina V neurons. The fractal dimension of the intracortical axon collateral arborizations of the same pyramidal neurons indicated, in all cases, that the branching of these terminals is less complex than the branching of the dendrites of the same cells. In line with the observation that the fractal dimensions of some homologous cellular populations are different in different species, it is suggested that the fractal dimension and the degree of morphological complexity may relate to the requirement for the number of separable functions to be accommodated within one neuron. For example, as the size of the cortex and the number of neurons in a region increase, the opportunity exists within a given cortical zone, for individual functions to be segregated and for functional specialization to be accommodated with less morphological complexity of the individual neurons performing each of these functions.

Animals↗
PubMed2003

Primary motor cortex stimulation within the central sulcus for treating deafferentation pain.

Nine patients with post-stroke pain, six with brachial plexus injuries, two with phantom limb pain, one with spinal cord injury, and one with brain stem injury were treated with a modified motor cortex stimulation (MCS) protocol. Preoperative pharmacological tests were performed with phentolamine, lidocaine, ketamine, thiopental, morphine, and placebo. We placed a grid electrode in the subdural space to decide upon the best stimulation point for pain relief over a few weeks with the purpose of determining the placement of a Resume electrode. In five patients, Resumes were implanted in the interhemispheric fissure to reduce lower extremity pain. In five other patients, Resumes were placed within the central sulcus to stimulate area 4 and area 3b. In addition, electrodes were also placed on the surface of the precentral gyrus. Fourteen of the 19 patients showed pain reduction (6 excellent, 3 good, and 5 fair) using the MCS with our results indicating area 4 within the central sulcus to be the optimal stimulation point for pain relief. We speculate that conventional method may sometimes fail to stimulate area 4 and that focal stimulation of the primary motor cortex within the central sulcus may improve the efficacy of this treatment. Our pharmacological tests show that patients with ketamine sensitivity seem to be good candidates for MCS. Test stimulation with a subdural multi-grid electrode and Resumes in the cetral sulcus were helpful in locating the best stimulation point for pain relief.

Adult↗
PubMed1994

Protracted postnatal development of corticospinal projections from the primary motor cortex to hand motoneurones in the macaque monkey.

We have studied the development of corticospinal projections from the hand area of the primary motor cortex to the spinal cord using anterograde transport of WGA-HRP. In the neonate, as in the adult, corticospinal projections to the intermediate zone at the C8/T1 spinal level were clearly present. However, in contrast to the adult, there was only very faint and barely visible labelling in the dorso-lateral motor nuclei which supply the hand muscles. No aberrant projections to other motor nuclei were seen. By 2.5 months, a ring of dense labelling was present around the dorso-lateral motor nuclei, but labelling was still sparse in the central region. This labelling was more pronounced at 11 months, but was still not as heavy as in the adult. There was no labelling among the ventral motoneurones at any age. The conduction velocity (c.v.) of the fastest corticospinal fibres was determined in each of the monkeys. There was an age-related increase in c.v. within the spinal cord. At birth, the fastest axons had a c.v. of only 8 m.s-1. At 11 months c.v. was still substantially slower (55 m.s-1) than the adult value of 73 m.s-1. In contrast, by 11 months, the axonal c.v. within the brain was close to the adult value, suggesting a rostro-caudal maturation of the corticospinal system. Our results demonstrate that corticospinal projections in the macaque monkey mature gradually over a period of at least 11 months, much longer than previously thought.

Animals↗
PubMed1990

Chronic focal epilepsy induced by microinjection of tetanus toxin into the cat motor cortex.

The tetanus toxin model of epilepsy, involving direct microinjection of toxin into the mammalian brain, has a number of advantages relative to other chronic models. However, chronic seizure foci have been confined primarily to the hippocampus. In the present study, 5 cats received total doses of 7.5-22.5 ng of tetanus toxin applied to the left primary motor cortex through an epidural cannula. After 2-18 days, all 5 cats exhibited similar persistent epileptiform syndromes. Three distinct types of spontaneous seizures were noted: focal motor seizures of variable complexity, focal motor seizures with secondary generalization, and epilepsia partialis continua. All cats required anticonvulsant therapy. Simple focal motor seizures, which predominated, were electrographically characterized by 3-5 Hz spike-sharp wave activity, originating in the left motor cortex, associated with contralateral shoulder and forepaw clonus and jacksonian spread. Electrographic activity quickly spread to ipsilateral neocortical structures, and in longer episodes to the cingulate gyri. Seizure foci were still active as long as 37 days after toxin injection. Light microscopic damage attributable to the toxin was absent. These experiments further generalized the tetanus toxin model and confirmed its advantages.

Animals↗
PubMed2003

Dynamical organization of directional tuning in the primate premotor and primary motor cortex.

Although previous studies have shown that activity of neurons in the motor cortex is related to various movement parameters, including the direction of movement, the spatial pattern by which these parameters are represented is still unresolved. The current work was designed to study the pattern of representation of the preferred direction (PD) of hand movement over the cortical surface. By studying pairwise PD differences, and by applying a novel implementation of the circular variance during preparation and movement periods in the context of a center-out task, we demonstrate a nonrandom distribution of PDs over the premotor and motor cortical surface of two monkeys. Our analysis shows that, whereas PDs of units recorded by nonadjacent electrodes are not more similar than expected by chance, PDs of units recorded by adjacent electrodes are. PDs of units recorded by a single electrode display the greatest similarity. Comparison of PD distributions during preparation and movement reveals that PDs of nearby units tend to be more similar during the preparation period. However, even for pairs of units recorded by a single electrode, the mean PD difference is typically large (45 degrees and 75 degrees during preparation and movement, respectively), so that a strictly modular representation of hand movement direction over the cortical surface is not supported by our data.

Animals↗
PubMed1993

Cognitive neurophysiology of the motor cortex.

A major challenge of current neuroscience is to elucidate the brain mechanisms that underlie cognitive function. There is no doubt that cognitive processing in the brain engages large populations of cells. This article explores the logic of investigating these problems by combining psychological studies in human subjects and neurophysiological studies of neuronal populations in the motor cortex of behaving monkeys. The results obtained show that time-varying psychological processes can be visualized in the time-varying activity of neuronal populations. Moreover, the functional interactions between cells in the motor cortex are very similar to those observed in a massively interconnected artificial network performing the same computation.

Animals↗
PubMed2004

Post-spike distance-to-threshold trajectories of neurones in monkey motor cortex.

A recently developed method permits calculation of the post-spike distance-to-threshold trajectory from an extracellularly recorded spontaneous spike train, using a transform of the interspike interval histogram. We applied this method to 61 single neurones recorded from the primary motor cortex of an awake behaving monkey; 39 cells were antidromically identified as pyramidal tract neurones (PTNs). The cells fell into three categories. Fifty-three trajectories (37 from PTNs) had statistically significant peaks 10-60 ms after the preceding spike. Six neurones (2 PTNs) had non-peaked trajectories which rose exponentially towards threshold. Two cells (both unidentified) had trajectories which declined monotonically away from threshold with increasing post-spike latency. The peaked trajectories were unlikely simply to be an artefact of changing firing rate, which potentially can invalidate this method. Firstly, computer simulations confirmed that the method could accurately re-create both exponential and peaked trajectories, even in the presence of the same rate modulation as seen experimentally. Secondly, the responses of eight cells to weak single pulse intracortical microstimulation (20 microA) through a nearby electrode were measured. For each cell, including representatives of all three trajectory shapes, the modulation of response probability with post-spike latency was consistent with the trajectory computed from the spontaneous discharge. We also demonstrated that cells showed a peaked trajectory during periods with either high or low spontaneous network oscillations, so that the peaks were likely to be generated in part by single cell properties rather than exclusively by network activity. We conclude that many single neurones in motor cortex have an increased probability of firing a spike around 30 ms after the previous action potential. This could act to enhance synchronized oscillatory discharge among populations of cells at functionally relevant frequencies.

Action Potentials↗