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PubMed1994

Information processing within the motor cortex. II. Intracortical connections between neurons receiving somatosensory cortical input and motor output neurons of the cortex.

Connections between motor cortical neurons receiving somatosensory inputs from area 2 and large pyramidal cells in layer V were examined in the cat via intracellular injection of biocytin and immunohistochemistry of nonphosphorylated neurofilament proteins (npNFP). Biocytin was injected into pyramidal cells in layers II/III of the motor cortex that responded monosynaptically and polysynaptically to microstimulation of the somatosensory cortex and subsequently stained black by the avidin-biotinylated peroxidase complex method with diaminobenzidine (DAB) and nickel. By using a monoclonal antibody SMI-32 and a modified peroxidase-antiperoxidase method with Tris-aminophenyl-methane (TAPM) and p-cresol as a chromogen, pyramidal cells in layers III and V of the motor cortex were stained red for npNFP. In particular, all the large pyramidal cells in layer V, Betz cells, displayed intense npNFP immunoreactivity not only in the perikarya but also in the dendrites. Double staining with DAB/nickel and TAPM/p-cresol showed that biocytin-filled axon varicosities of the pyramidal cells, which were thought to receive monosynaptic inputs from area 2, made contacts with npNFP-positive dendrites in layers I-III around the biocytin-injected cell and in layers V-VI beneath the cell. The present results suggest that the corticocortical input from area 2 to pyramidal cells in layers II/III of the motor cortex is transferred to layer V pyramidal cells, including Betz cells, as well as to neighboring layer II/III pyramidal cells. Since tetanic stimulation of the somatosensory cortex reportedly produces long-term potentiation in layer II/III cells of the motor cortex, it seems reasonable to assume that a given area of the somatosensory cortex can produce a long-lasting change in the activity of a given group of output cells in the motor cortex.

Animals↗

PubMed1993

Intracortical mechanisms for the recruitment of motor cortex neurons.

Neurons project out of motor cortex to the spinal cord and to other targets. Not all projection neurons recruit in the same way during behavior, but instead recruitment patterns depend on the projection target of the neurons. The problem is to understand how neurons projecting to different targets are recruited selectively. We have investigated possible mechanisms for the recruitment of motor cortex neurons with electrophysiological approaches in anesthetized cats. To determine if neurons projecting out of motor cortex to different targets have selective input connectivity from extrinsic sources we electrically stimulated corticocortical, callosal and thalamocortical pathways. Subthreshold effects of input pathways were detected by monitoring latency variations of antidromic responses. Intracortical connections to identified output neurons were evaluated by cross-correlation and a new variation of the antidromic latency method. Output neurons in different layers along single electrode tracks usually had different inputs from extrinsic sources. Neurons in close proximity were most likely to share the same inputs, especially when they projected axons to the same target. These results support the conclusion that combinations of inputs from extrinsic sources could selectively recruit efferent neurons from separate cortical layers or from within groups of nearby neurons, according to the target of their axonal projections. In contrast, the data on intracortical connectivity suggest that common drive causes a more synchronous activation of nearby cortical neurons. Combining the conclusions on effects of inputs from extrinsic and intracortical sources leads to the speculation that motor cortex neurons that might at one time be recruited selectively by action of extrinsic afferent pathways to cortex could at another time be bound into synchrony by a common drive shared with their neighbours.

Animals↗

PubMed1998

Involvement of NMDA and non-NMDA receptors in the neuronal responses of the primary motor cortex to input from the supplementary motor area and somatosensory cortex: studies of task-performing monkeys.

The involvement of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in mediating the excitatory responses of neurons in the primary motor cortex (MI) to electrical stimulation of the supplementary motor area (SMA) and the somatosensory cortex (SI) was examined in monkeys performing a trained motor task. During the task, a total of 109 MI neurons were identified and classified as movement related (91), motor set related (7), or mixed (11). Subsequently, the influence of receptor antagonists on the stimulus-evoked and task-related activities of these neurons was examined. The selective NMDA antagonist D-2-amino-5-phosphonovaleric acid (APV) and the selective non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were applied iontophoretically through multibarreled micropipettes. One barrel was used for extracellular unit recording. The excitatory response evoked by SI stimulation was suppressed by CNQX in the vast majority (83%) of the motor task related neurons, and only 10% were suppressed by APV. On the other hand, the response evoked by SMA stimulation was suppressed by APV in 56% of the neurons and by CNQX in 54%. APV and CNQX had parallel effects on the stimulus-evoked responses and the task-related neuronal activity. These results indicate that NMDA and non-NMDA receptors are both involved in mediating the excitatory responses of MI neurons to input from the SMA and SI. On the other hand, the data suggest a greater contribution of non-NMDA receptors in response to SI input and greater involvement of NMDA receptors in mediating the response to SMA input, especially among set-related MI neurons.

2-Amino-5-phosphonovalerate↗

PubMed2003

Synaptic mitochondrial changes in the motor cortex following unilateral cortical lesions and motor skills training in adult male rats.

Unilateral lesions of the forelimb sensorimotor cortex and motor skills training interact to enhance synaptic plasticity in layer V of the motor cortex contralateral to the lesion in male rats. In this study, we assessed the metabolic correlates of these synaptic changes by quantifying the number and size of mitochondria in synaptic axonal terminals with perforated or non-perforated post-synaptic densities (PSDs) and single or multiple post-synaptic contacts. The number of synaptic mitochondria per neuron was significantly greater in rats with lesions. Neither manipulation affected mitochondrial size or number of mitochondria per synapse. Independent of experimental condition, terminals with perforated PSDs had more mitochondria than those with non-perforated PSDs and, among those with non-perforated PSDs, terminals with multiple synaptic contacts had more mitochondria than those forming single synapses.

Adaptation, Physiological↗

PubMed1995

[Motor reorganization in the motor cortex].

Plasticity within the human central motor system has been studied with transcranical magnetic stimulation in patients with peripheral and central nervous diseases. In 4 patients with a complete upper limb palsy due to traumatic cervical root avulsion, surgical anastomosis of intercostal to musculocutaneous nerves was performed to restore function in the biceps brachii muscle. The motor unit discharges became independent from respirations gradually over 1 to 2 years. Motor cortex mapping of the reinnervated biceps muscle showed a gradual change over 4 to 33 months from the area of the intercostal muscles to that of the arm area, which was more lateral on the motor cortex. These findings suggest that reorganization of the motor cortex to arm flexor muscles occurs following peripheral nerve anastomosis. In 8 patients with chronic cerebral infarction with hemiplegia. Four of 8 patients did not show MEPs in paralytic hand muscles by contralateral cortex stimulation, but showed small MEPs by ipsilateral cortex stimulation. These cases had the huge cortical infarction unilaterally in CT. Another four of 8 patients showed small MEPs in paralytic hand muscles by contralateral cortex stimulation, but no MEPs by ipsilateral cortex stimulation. These cases had the subcortical infarction unilaterally in CT. These findings suggest that reorganization of motor cortex following unilateral cerebral infarction.

Anastomosis, Surgical↗

PubMed1995

Vibrissal motor cortex in the rat: connections with the barrel field.

The flow of information in the sensorimotor cortex may determine how somatic information modulates motor cortex neuronal activity during voluntary movement. Electrophysiological recordings and neuroanatomical tracing techniques were used to study the connections between the primary somatosensory cortex (SI) and the vibrissal representation of the primary motor cortex (MI) in rodents. Intracortical microstimulation (ICMS) was applied to the vibrissal region of the motor cortex to identify a site from which stimulation evoked movements of the vibrissae. Movements of only a single whisker were evoked by applying low-intensity stimulating current to particular locations within MI. A single injection of either horseradish peroxidase (HRP) or biocytin was made at the stimulus site in each animal, to retrogradely label cells in the somatosensory cortex. Receptive field (RF) responses were recorded from neurons in the barrel cortex to identify the sensory cortex representation of the same whisker that responded to ICMS. The site at which neurons responded predominately to manual stimulation of this particular vibrissa was marked by a small electrolytic lesion. The projection from the somatosensory cortex to the identified whisker representation in the motor cortex was determined by mapping the location of labeled neurons in tissue sections processed for either HRP or biocytin. The relationship of the labeled cells in SI to the barrel structures was determined from adjacent sections that were stained for cytochrome oxidase. In all cases, the barrel column associated with the relevant whisker contained labeled cells. Surrounding barrels also contained labeled cells, although fewer in number. Very few labeled cells were found in non-contiguous barrels. These results show that the SI to MI projection is somatotopically arranged, such that the sensory cortex representation of a whisker is morphologically connected to the motor cortex representation of the same whisker. Thus, sensory information is relayed to MI from the relevant whisker region in SI. Adjacent whisker regions also appear to relay somatic input, but presumably to a lesser degree. A second group of animals received single small injections of the anterograde tracer, Phaseolus vulgaris leucoagglutinin, to an electrophysiologically identified whisker representation in the sensory cortex. A single narrow column of labeled fibers was found in the motor cortex following such injections. Thus, the sensory cortex appears to relay somatic information from the vibrissae to restricted regions of the motor cortex in a somatotopically organized manner. Furthermore, the stimulus-evoked whisker movements suggest that certain features of the output map of the motor cortex are discretely organized.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed2004

Whisker movements evoked by stimulation of single pyramidal cells in rat motor cortex.

Neuronal activity in the motor cortex is understood to be correlated with movements, but the impact of action potentials (APs) in single cortical neurons on the generation of movement has not been fully determined. Here we show that trains of APs in single pyramidal cells of rat motor cortex can evoke long sequences of small whisker movements. For layer-5 pyramids, we find that evoked rhythmic movements have a constant phase relative to the AP train, indicating that single layer-5 pyramids can reset the rhythm of whisker movements. Action potentials evoked in layer-6 pyramids can generate bursts of rhythmic whisking, with a variable phase of movements relative to the AP train. An increasing number of APs decreases the latency to onset of movement, whereas AP frequency determines movement direction and amplitude. We find that the efficacy of cortical APs in evoking whisker movements is not dependent on background cortical activity and is greatly enhanced in waking rats. We conclude that in vibrissae motor cortex sparse AP activity can evoke movements.

Action Potentials↗

PubMed1988

Spatial coding of visually guided arm movements in primate motor cortex.

Previous studies of the motor cortex in behaving animals were focused on the relations between the activity of single cells, usually pyramidal tract neurons, and parameters of isometric contraction (e.g., intensity of force) or parameters of movement along one axis (e.g., flexion-extension) of a single joint (e.g., elbow or wrist). However, the commonly meaningful behavioral parameter is the trajectory of the hand in extrapersonal space, which is realized by simultaneous motions about two or three joints (e.g., elbow, shoulder, wrist) and concurrent engagement of several muscles. The spatial parameters of a straight trajectory are its direction and extent. We hypothesized that a major function of the motor cortex, among other possible roles, is the specification and control of the direction of the movement trajectory in space. This reference of motor cortical function to the control of spatial aspects of the trajectory differentiated our approach from the other approaches outlined above. We investigated the directional selectivity cells in the arm area of the motor cortex by recording their activity while monkeys moved their hands in various directions in space towards visual targets. There were two salient findings of these studies. First, the intensity of the discharge of single cells varies in an orderly fashion with the direction of movement in space, so that the discharge rate is highest with movements in a preferred direction, and decreases progressively with movements made in directions more and more away from the preferred one. Thus single cells are broadly tuned around a preferred direction which differs among different cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

[Local disinhibition with bicuculline does not break the trained relationship between afferent input and efferent output in cat motor cortex].

Neurons of the cat motor cortex related to the lifting-withdrawal phase of forepaw placing reaction are preferentially activated by tactile stimulation of the dorsal surface of the forepaw. The placing reaction was altered in such a way that the innate "dorsal placing" was subjected to extinction and was substituted for the newly acquired conditioned reaction in response to the ventral side stimulation. This alteration of placing reaction led to the inversion of the innate input-output relationship in the motor cortex. The neurons related to forepaw lifting-withdrawal began to be activated by tactile stimulation of the ventral rather than dorsal forepaw surface. Local cortical disinhibition by bicuculline application at the recording site qualitatively changed neither normal input-output relationships nor inverse relationships after placing reaction alteration. This suggests that alteration of the sensorimotor coordination in cat motor cortex is underlain by changes in excitatory rather than inhibitory connections.

Animals↗

PubMed1986

Functional organization of thalamic projections to the motor cortex. An anatomical and electrophysiological study in the rat.

In rats, horseradish peroxidase crystals were injected in motor cortical foci functionally identified by means of the motor effects evoked by electrical stimulations. The location in the thalamus of the neurons linked to different motor cortical foci was studied. Thalamic neurons were retrogradely labeled in both "motor" (ventralis lateralis and ventralis medialis) and "non-motor" nuclei: centralis lateralis, lateralis posterior, mediodorsalis and posterior thalamic nuclear group, as well as the ventrobasal complex. The ventrobasal complex was labeled after horseradish peroxidase injections in hindlimb and trunk motor areas. The ascending projections toward the motor cortex from both "motor" and "non-motor" thalamic nuclei are organized more precisely and more elaborately than previously reported. The motor cortical afferents from the nucleus ventralis lateralis are organized in three planes, rostrocaudally, dorsoventrally and mediolaterally. An inverted relation exists in the rostrocaudal plane between the nucleus ventralis lateralis and the motor cortex: the caudal motor cortex region (hindlimb) receives fiber inputs from the rostral region of the nucleus ventralis lateralis, whereas the caudal zone of the nucleus ventralis lateralis projects to the rostral motor cortex region (forelimb and vibrissae). A dorsoventral organization has also been observed in the rostral region of the nucleus ventralis lateralis: the ventral aspect is the source of fibers directed to the distal hindlimb region, whereas fibers originating from the dorsal aspect are directed to the proximal hindlimb area. A mediolateral relationship exists between medial and lateral sides of the nucleus ventralis lateralis and, respectively, proximal and distal forelimb cortical areas. There is some overlap between the various nuclear regions thus delineated. Four functional zones were found in the lateral half of the nucleus ventralis medialis and were classified according to their projection to the motor cortex; these are involved in motor control of the proximal and distal forelimb, vibrissae and ocular movements. The projection is topographically organized according to both an inverted rostrocaudal and a direct dorsoventral-mediolateral arrangement. Caudally, dorsal and ventral nuclear parts project to rostromedial (vibrissae) and rostrolateral (distal forelimb) regions of the motor cortex, respectively. More rostral nuclear zones project to more caudal (proximal forelimb, eye) cortical regions. There is little overlap between these four nuclear subdivisions. The nucleus centralis lateralis projects to vibrissae and proximal, as well as distal, forelimb areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Motor potentials evoked by magnetic stimulation of the motor cortex in normal subjects and patients with motor disorders.

Motor evoked potentials (MEPs) elicited by magnetic coil stimulation of motor cortex were studied at rest and during maximum voluntary muscle contraction in 20 normal subjects and 42 patients with motor disorders. MEP parameters employed in this study included: onset latency, amplitude, MEP/M wave amplitude ratio and background EMG/MEP area ratio. Maximum voluntary contraction increased the amplitude of MEPs compared to the size of M waves elicited by peripheral nerve stimulation. A reduced MEP/M wave amplitude ratio had a higher correlation with pyramidal tract involvement than did a prolonged MEP onset latency. Analysis of MEP parameters may help in the differential diagnosis of cerebral infarction, ALS and cervical spondylotic radiculomyelopathy. The inhibitory period which follows MEPs during voluntary contraction was observed in all subjects; the mean duration in normal subjects was 126.6 +/- 29.5 msec. The mean duration of the inhibitory period in patients with cerebral infarction, ALS and cervical spondylotic radiculomyelopathy was 73.9 +/- 41.7 msec, 79.5 +/- 54.5 msec and 85.1 +/- 36.5 msec, respectively. These values were significantly shorter than in normal subjects.

Adult↗

PubMed1992

Functional properties of single neurons in the face primary motor cortex of the primate. II. Relations with trained orofacial motor behavior.

1. The previous paper has described in detail the input and output features of single neurons located at sites within primate face motor cortex from which intracortical microstimulation (ICMS, less than or equal to 20 microA) evoked tongue movements at the lowest threshold ("tongue-MI" sites); for comparative purposes, we also reported on the input and output features of a smaller number of neurons recorded at sites from which ICMS could evoke jaw movements ("jaw-MI" sites), facial movements ("face-MI" sites), or, at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 2. Our findings of an extensive and diverse representation of sites within face motor cortex of monkeys for the generation of elemental components of tongue movement, and the relatively few sites from which jaw-closing movements could be evoked, were consistent with our recent observations that reversible, cooling-induced inactivation of the face motor cortex severely impaired the performance by monkeys of a tongue-protrusion task but had only relatively minor effects on the performance of a biting task. In an attempt to establish a neuronal correlate for these different behavioral relations, the present study has documented the task-related activities of those single neurons that were characterized in the previous paper in terms of afferent input and ICMS-defined output features. 3. Each task required the development and maintenance by each monkey of a fixed force level for a minimum period of time to obtain a fruit-juice reward. During one or both of these tasks, we characterized the activities of 231 single face motor cortical neurons that were located at the above-mentioned ICMS-defined sites. Neurons were said to be related to a particular task if they showed statistically significant differences in firing rates during the task in comparison with a control pretrial period (PTP). 4. In tongue-MI, there was a significantly higher proportion of neurons (63% of 156 neurons tested) that were related to the tongue-protrusion task than to the biting task (15% of 65). However, in jaw-MI the proportion of neurons that were biting task-related (63% of 19) was significantly higher than the proportion related to the tongue-protrusion task (11% of 9); the proportion of biting task-related neurons at ICMS-defined jaw-closing sites was also higher than that at jaw-opening sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2006

Somatotopic organization of the analgesic effects of motor cortex rTMS in neuropathic pain.

BACKGROUND: Motor cortex repetitive transcranial magnetic stimulation (rTMS) was found to relieve chronic neuropathic pain, but the optimal parameters of stimulation remain to be determined, including the site of stimulation. OBJECTIVE: To determine the relationship between cortical stimulation site and pain site regarding the analgesic efficacy of rTMS of motor cortex in chronic neuropathic pain. METHODS: Thirty-six patients with unilateral chronic neuropathic pain located at the face or the hand were enrolled. Motor cortex rTMS was applied at 10 Hz over the area corresponding to the face, hand, or arm of the painful side, whatever pain location. Analgesic effects were daily assessed on visual analogue scale for the week that followed each rTMS session. RESULTS: All types of rTMS session, whatever the target, significantly relieved pain, compared with baseline. However, analgesic effects were significantly better after hand than face area stimulation in patients with facial pain and after face than hand or arm area stimulation in patients with hand pain. CONCLUSION: Repetitive transcranial magnetic stimulation was more effective for pain relief when the stimulation was applied to an area adjacent to the cortical representation of the painful zone rather than to the motor cortical area corresponding to the painful zone itself. This result contradicts the somatotopic efficacy observed for chronic epidural motor cortex stimulation with surgically implanted electrodes.

Adult↗

PubMed2001

Interactions between two different inhibitory systems in the human motor cortex.

Intracortical inhibition in the human motor cortex has been previously demonstrated using paired-pulse transcranial magnetic stimulation (TMS) protocols at short intervals (1-6 ms; short interval intracortical inhibition, SICI) with a subthreshold conditioning pulse preceding a suprathreshold test pulse, and at long intervals (50-200 ms; long interval intracortical inhibition, LICI) with suprathreshold conditioning and test pulses. We investigated whether different circuits mediate these inhibitory phenomena and how they interact. In nine healthy volunteers, we applied TMS to the motor cortex and recorded motor evoked potentials from the first dorsal interosseous muscle. With increasing test pulse strength, LICI decreases but SICI tends to increase. There was no correlation between the degree of SICI and LICI. We tested the interactions between SICI and LICI. SICI was reduced or eliminated in the presence of LICI. Loss of SICI was seen even with a conditioning stimulus too weak to induce significant LICI. Our findings demonstrate that different cell populations mediate SICI and LICI. The results are consistent with the hypothesis that LICI inhibits SICI through presynaptic GABAB receptors. Testing of SICI in the presence of LICI may be a non-invasive way of evaluating inhibitory interactions in the human motor cortex.

Adult↗

PubMed2003

Prolonged exercise induces angiogenesis and increases cerebral blood volume in primary motor cortex of the rat.

Plastic changes in motor cortex capillary structure and function were examined in three separate experiments in adult rats following prolonged exercise. The first two experiments employed T-two-star (T(2)*)-weighted and flow-alternating inversion recovery (FAIR) functional magnetic resonance imaging to assess chronic changes in blood volume and flow as a result of exercise. The third experiment used an antibody against the CD61 integrin expressed on developing capillaries to determine if motor cortex capillaries undergo structural modifications. In experiment 1, T(2)*-weighted images of forelimb regions of motor cortex were obtained following 30 days of either repetitive activity on a running wheel or relative inactivity. The proton signal intensity was markedly reduced in the motor cortex of exercised animals compared with that of controls. This reduction was not attributable to alterations of vascular iron levels. These results are therefore most consistent with increased capillary perfusion or blood volume of forelimb regions of motor cortex. FAIR images acquired during experiment 2 under normocapnic and hypercapnic conditions indicated that resting cerebral blood flow was not altered under normal conditions but was elevated in response to high levels of CO(2), suggesting that prolonged exercise increases the size of a capillary reserve. Finally, the immunohistological data indicated that exercise induces robust growth of capillaries (angiogenesis) within 30 days from the onset of the exercise regimen. Analysis of other regions failed to find any changes in perfusion or capillary structure suggesting that this motor activity-induced plasticity may be specific to motor cortex.These data indicate that capillary growth occurs in motor areas of the cerebral cortex as a robust adaptation to prolonged motor activity. In addition to capillary growth, the vascular system also experiences heightened flow under conditions of activation. These changes are chronic and observable even in the anesthetized animal and are measurable using noninvasive techniques.

Aging↗

PubMed2026

High-frequency contralesional dorsal premotor cortex and low-frequency contralesional primary motor cortex rTMS in subacute stroke with severe upper limb impairment: comparable motor outcomes and differential regional degree centrality changes.

BACKGROUND: The contralesional dorsal premotor cortex has been proposed as a potential neuromodulatory target for patients with severe upper limb impairment due to subacute ischemic stroke. This proof-of-concept study aimed to compare behavioral outcomes and resting-state neuroimaging findings between high-frequency repetitive transcranial magnetic stimulation (rTMS) over the contralesional dorsal premotor cortex and guideline-supported low-frequency stimulation over the contralesional primary motor cortex. METHODS: In this randomized trial, 46 patients with severe upper limb impairment in the subacute stage after ischemic stroke were randomly assigned to receive either high-frequency rTMS over the contralesional dorsal premotor cortex or low-frequency rTMS over the contralesional primary motor cortex. Low-frequency stimulation over the contralesional primary motor cortex served as an evidence-supported active comparator for poststroke upper limb motor recovery. Stimulation was administered five times per week for two weeks using magnetic resonance imaging-guided neuronavigation. All participants received concurrent standard rehabilitation therapy. The primary outcome was the Fugl-Meyer Assessment for Upper Extremity. Secondary outcomes included the Arm Subscore of the Motricity Index, the Hong Kong version of the Functional Test for the Hemiplegic Upper Extremity, the Modified Barthel Index, and resting-state functional magnetic resonance imaging-derived degree centrality. RESULTS: Both groups showed significant improvements in the primary and secondary behavioral measures (p < 0.01), with no significant between-group differences in the magnitude of change (p > 0.05). In neuroimaging analyses, patients receiving high-frequency rTMS over the contralesional dorsal premotor cortex showed significantly greater degree centrality changes in the ipsilesional middle occipital gyrus, contralesional medial superior frontal gyrus, and contralesional middle frontal gyrus than those receiving low-frequency rTMS over the contralesional primary motor cortex (p < 0.05). Within the high-frequency stimulation group, degree centrality changes in the ipsilesional middle occipital gyrus were positively correlated with improvements in the Fugl-Meyer Assessment for Upper Extremity (r = 0.619, false discovery rate-corrected p = 0.018). CONCLUSIONS: High-frequency rTMS over the contralesional dorsal premotor cortex produced behavioral improvements comparable to guideline-supported low-frequency rTMS over the contralesional primary motor cortex, without establishing superiority or formal non-inferiority. Exploratory neuroimaging analyses showed greater degree centrality changes in the ipsilesional middle occipital gyrus after high-frequency premotor stimulation, and these changes correlated with upper-limb motor improvement. These findings support further investigation of contralesional dorsal premotor cortex-targeted high-frequency rTMS for severe subacute post-stroke upper limb impairment. REGISTRATION: URL: http://www.chictr.org.cn; Unique identifier: ChiCTR2000038049.

Humans↗

PubMed2006

Oxygenation in the motor cortex during exhaustive pinching exercise.

The purpose of this study was to examine the effect of fatigue resulting from exhaustive pinching exercise on frontal and motor cortex activity. Eight healthy subjects (four male and four female) participated in the present study. All subjects performed at 70% of maximal voluntary contraction (MVC) pinching exercise until reaching a state of volitional fatigue. Frontal cortex and motor cortex oxygenation was measured by near-infrared spectroscopy throughout the exhaustive exercise. Frontal cortex and motor cortex oxygenation increased significantly at the 90 and 120 s after the start of exercise compared with the pre-exercise values and these decreased with the time passage. Frontal cortex oxygenation at exhaustion was significantly lower than the 90 and 120 s after the start of exercise, while motor oxygenation at exhaustion was the same value with the pre-exercise value. These findings suggest that the exhaustive exercise induces the decrease of cerebral function and that the fatigue resulting from dynamic exercise decreases the motor cortex activity.

Adult↗

PubMed1991

Intra-operative recording of motor tract potentials at the cervico-medullary junction following scalp electrical and magnetic stimulation of the motor cortex.

Activity in descending motor pathways after scalp electrical and magnetic brain stimulation of the motor cortex was recorded from the exposed cervico-medullary junction in six patients having trans-oral surgery of the upper cervical spine. Recordings during deep anaesthesia without muscle paralysis revealed an initial negative potential (D wave) at about 2 ms with electrical stimulation in five of the six patients. This was followed by a muscle potential which obscured any later waveforms. Magnetic stimulation produced clear potentials in only one patient. The earliest wave to magnetic stimulation during deep anaesthesia was 1-2 ms later than the earliest potential to electrical stimulation. Following lightening of the anaesthetic and the administration of muscle relaxants a series of later negative potentials (I waves) were more clearly seen to both electrical and magnetic stimulation. More I waves were recorded to magnetic stimulation during light anaesthesia than during deep anaesthesia. Increasing the intensity of electrical stimulation also produced an extra late I wave. At the highest intensity of magnetic stimulation the latency of the earliest potential was comparable to the D wave to electrical stimulation. The intervals between these various D and I waves corresponded to those previously described for the timing of single motor unit discharge after cortical stimulation.

Adult↗