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PubMed2005

Bradykinesia induced by dopamine D2 receptor blockade is associated with reduced motor cortex activity in the rat.

Disruption of motor cortex activity is hypothesized to play a major role in the slowed movement (bradykinesia) associated with reduced dopaminergic function. We recorded single neurons in the motor cortex of free-moving rats performing a forelimb-reaching task. The same neurons were examined before and after induction of bradykinesia with the D2 dopamine receptor antagonist haloperidol. Within-cell changes in the firing rate and firing pattern of individual cells and the correlation between simultaneously recorded cells after injection of haloperidol were statistically compared with vehicle-only control experiments. During haloperidol-induced bradykinesia (mean movement time increase, +231%), there was an average 11% decrease in baseline firing rate. Movement-related peaks in firing rate were more dramatically affected, with an overall reduction in peak amplitudes of 40%. Bradykinesia was also associated with decreased intensity of bursting and amplitude of cross-correlation peaks at rest. The results show for the first time that significant reductions can be detected in motor cortex activity at rest in animals with impaired ability to generate movements induced by reduced dopamine action and confirm that impaired movements are associated with reduced cortical activation. Together, these changes in neural activity may reduce recruitment and rate modulation of motor units in the spinal cord.

Animals↗

PubMed1993

Comparison of cerebellar and motor cortex activity during reaching: directional tuning and response variability.

1. The responses of 262 motor cortex cells and 223 cerebellar neurons were recorded during whole-arm reaching movements toward targets lights in eight evenly distributed directions radiating from a common central starting position. The reaching movements were followed by a 2-s target hold period where a fixed arm posture was actively maintained to stabilize the hand over the target light. 2. Cerebellar neurons had a higher mean tonic discharge rate while holding over the starting position (22.9 imp/s) than did motor cortex cells (12.5 imp/s). The mean population response curve describing the changes in activities with movement direction was likewise shifted toward higher frequencies in the cerebellum compared with the motor cortex, but the amplitude of the two curves was about equal. Therefore, the baseline discharges of cerebellar neurons were higher, but their changes in activity during movement were similar to those of motor cortical cells. 3. Motor cortex neurons were more strongly related to active maintenance of different arm postures than were cerebellar units. This was shown by a larger posture-related population response curve in the motor cortex (half-wave amplitude of cosine function was 11.2 imp/s, compared with 7.0 imp/s for cerebellar neurons), which represented the average response curve calculated from all the cells of the population. Furthermore, the motor cortex population had a higher percentage of single cells with tonic responses while the hand was held over different targets (tonic and phasic-tonic cells composed 57% of motor cortex population, compared with 38% of cerebellar population). Proportionately more cerebellar cells were phasically related to the movements. 4. The majority of motor cortex cells (58%) showed reciprocal changes relative to the center-hold time activity where the activity increased for movements in the preferred direction and decreased for movements in the opposite direction. Most of the remaining cells (40%) showed graded changes where the activity increased gradually as reaching was directed closer to the preferred direction. In contrast, the most common cerebellar response pattern was graded (38%). Only 26% were reciprocal and 18% were non-directional. The remaining 2% of motor cortical cells and 18% of cerebellar neurons could not be readily assigned to any of these three response classes. 5. Sector widths were calculated to measure the dispersion of individual cerebellar and motor cortical cell activities about the eight movement directions. Sector widths calculated from the absolute activities were always broader for cerebellar neurons (i.e., the cells were more broadly tuned).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1996

Differential spinal projections from the forelimb areas of the rostral and caudal subregions of primary motor cortex in the cat.

We used anterograde transport of WGA-HRP to examine the topography of corticospinal projections from the forelimb areas within the rostral and caudal motor cortex subregions in the cat. We compared the pattern of these projections with those from the somatic sensory cortex. The principal finding of this study was that the laminar distribution of projections to the contralateral gray matter from the two motor cortex subregions was different. The rostral motor cortex projected preferentially to laminae VI-VIII, whereas caudal motor cortex projected primarily to laminae IV-VI. Confirming earlier findings, somatic sensory cortex projected predominantly to laminae I-VI inclusive. We found that only rostral motor cortex projected to territories in the rostral cervical cord containing propriospinal neurons of cervical spinal segments C3-4 and, in the cervical enlargement, to portions presumed to contain Ia inhibitory interneurons. We generated contour maps of labeling probability on averaged segmental distributions of anterograde labeling for all analyzed sections using the same algorithm. For rostral motor cortex, heaviest label in the dorsal part of lamina VII in the contralateral cord was consistently located in separate medial and lateral zones. In contrast, no consistent differences in the mediolateral location of label was noted for caudal motor cortex. To summarize, laminae I-III received input only from the somatic sensory cortex, while laminae IV-V received input from both somatic sensory and caudal motor cortex. Lamina VI received input from all cortical fields examined. Laminae VII-IX received input selectively from the rostral motor cortex. For motor cortex, our findings suggest that projections from the two subregions comprise separate descending pathways that could play distinct functional roles in movement control and sensorimotor integration.

Animals↗

PubMed2000

Impairments in prehension produced by early postnatal sensory motor cortex activity blockade.

This study examined the effects of blocking neural activity in sensory motor cortex during early postnatal development on prehension. We infused muscimol, either unilaterally or bilaterally, into the sensory motor cortex of cats to block activity continuously between postnatal weeks 3-7. After stopping infusion, we trained animals to reach and grasp a cube of meat and tested behavior thereafter. Animals that had not received muscimol infusion (unilateral saline infusion; age-matched) reached for the meat accurately with small end-point errors. They grasped the meat using coordinated digit flexion followed by forearm supination on 82.7% of trials. Performance using either limb did not differ significantly. In animals receiving unilateral muscimol infusion, reaching and grasping using the limb ipsilateral to the infusion were similar to controls. The limb contralateral to infusion showed significant increases in systematic and variable reaching end-point errors, often requiring subsequent corrective movements to contact the meat. Grasping occurred on only 14.8% of trials, replaced on most trials by raking without distal movements. Compensatory adjustments in reach length and angle, to maintain end-point accuracy as movements were started from a more lateral position, were less effective using the contralateral limb than ipsilateral limb. With bilateral inactivations, the form of reaching and grasping impairments was identical to that produced by unilateral inactivation, but the magnitude of the reaching impairments was less. We discuss these results in terms of the differential effects of unilateral and bilateral inactivation on corticospinal tract development. We also investigated the degree to which these prehension impairments after unilateral blockade reflect control by each hemisphere. In animals that had received unilateral blockade between postnatal weeks (PWs) 3 and 7, we silenced on-going activity (after PW 11) during task performance using continuous muscimol infusion. We inactivated the right (previously active) and then the left (previously silenced) sensory motor cortex. Inactivation of the ipsilateral (right) sensory motor cortex produced a further increase in systematic error and less frequent normal grasping. Reinactivation of the contralateral (left) cortex produced larger increases in reaching and grasping impairments than those produced by ipsilateral inactivation. This suggests that the impaired limb receives bilateral sensory motor cortex control but that control by the contralateral (initially silenced) cortex predominates. Our data are consistent with the hypothesis that the normal development of skilled motor behavior requires activity in sensory motor cortex during early postnatal life.

Age Factors↗

PubMed1987

Examination of motor function in lesions of the spinal cord by stimulation of the motor cortex.

Electrical stimulation of the motor cortex was performed in 3 patients with cervical cord trauma and in 3 with cervical myelopathy caused by cervical spondylosis. Abnormal conduction in central motor tracts was demonstrated in 5 of the 6 patients; yet in 4 of these, cortical somatosensory evoked potentials from the same limb were of normal latency. In the remaining patient who had normal motor latencies, the somatosensory evoked potentials were delayed on one side. Electrophysiological examination of the motor pathways by cortical stimulation may therefore be of considerable value in the assessment and management of patients with traumatic and compressive disease of the spinal cord.

Adult↗

PubMed2006

Interactions between pairs of transcranial magnetic stimuli over the human left dorsal premotor cortex differ from those seen in primary motor cortex.

A single TMS pulse (110% resting motor threshold, RMT) to the left dorsal premotor cortex (PMd) (CS2) suppresses the amplitude of motor evoked potentials (MEPs) from a test pulse (TS) over the right motor cortex (M1), and facilitates MEPs from the left motor cortex. We probed how this interaction was changed by a prior conditioning pulse over PMd (CS1) using a paired pulse TMS design. In the main experiments, the intensity of CS1 was 80% RMT. Basal suppression of right M1 was removed when CS1-CS2 was 1 ms or 5 ms with a similar tendency at 15 ms. Basal facilitation of left M1 was suppressed at CS1-CS2 of 5 ms. A similar time course was seen if CS2 was increased to 100% RMT, but there was no significant effect if CS1 was 70% RMT. Preconditioning PMd with continuous or intermittent theta burst repetitive TMS (cTBS, iTBS) abolished the basal CS2-TS interaction between premotor and motor cortices. Finally, if very short interstimulus intervals between CS1 and CS2 were explored to detect interactions similar to I-wave facilitation in M1, we found that the basal suppression of right M1 was abolished at CS1-CS2 intervals of 1.8 and 2.8 ms. We suggest that paired pulse TMS may be capable of investigating properties of intrinsic circuits in PMd and that their properties differ from those in the nearby M1. Paired TMS may be a useful method of studying the excitability of intrinsic circuits in non-primary areas of the motor system.

Adult↗

PubMedDate not supplied

[The mechanism of movement instrumental learning in a Hopfield environment in the feline motor cortex].

A model of the neuronal processes in the motor cortex is proposed, which provides the mechanism for instrumentalization (voluntary reproduction) of movements primarily evoked by stimulation of the parietal cortex. The main propositions of the model are as follows: the late NMDA-dependent response of the motor cortex neurons to stimulation of the parietal cortex reflects the discharges in the recurrent collaterals of the pyramidal cell axons; learning processes in the motor cortex are based on the long-term potentiation of the efficiency of the recurrent collaterals; the Hopfield's theory of neuronal nets is applied to the processes of motor learning in the cortex. The movement instrumentalization is viewed as the stable state formation in the collaterally linked neuronal structure; the voluntary reproduction of the previously learned movement in considered as the process of transition of the neuronal structure into the stable state. The data on acetylcholine and dopamine modulatory influences on the reactions of motor cortex neurons are discussed.

Animals↗

PubMed2005

Motor cortex stimulation for central and neuropathic facial pain: a prospective study of 10 patients and observations of enhanced sensory and motor function during stimulation.

OBJECTIVE: For more than a decade, motor cortex stimulation has been used to treat difficult central and peripheral neuropathic pain syndromes. This prospective study uses the McGill Pain Questionnaire, a visual analog scale (VAS) score, and an inventory of drug consumption to review the results of treating patients with trigeminal neuropathic pain via motor cortex stimulation. METHODS: Ten patients underwent motor cortex stimulation between 1999 and 2002. Implantation was performed via intraoperative neuronavigation and cortical mapping for stimulation site targeting. Nine patients had trigeminal neuropathic pain from postherpetic neuralgia, surgical injury, or unknown cause, and one patient had pain of central origin. Patients were evaluated with multimodality scales before, immediately after, and at designated intervals after surgery. Eight patients underwent permanent implantation after a trial evaluation. In two patients, the stimulating electrodes were removed after an unsuccessful trial. One of these patients had a lateral medullary infarct leading to central pain, and in another patient, there was no explanation for the pain. RESULTS: The average duration of pain before surgery was 6 years. Postoperatively, there was an 88% rate of immediate pain relief (>50% on VAS) and a 75% rate of pain relief at mean follow-up of 10 months (range, 3-24 mo). Mean preoperative McGill Pain Questionnaire total pain rating index was 57 (higher than that observed in causalgia) for patients who did not undergo implantation and 53 for those who underwent implantation. Mean McGill Pain Questionnaire pain rating index at mean follow-up of 10 months was 24 (55% decrease). Mean VAS preoperatively was 9 in patients with stimulator implants and 8 in those whose stimulator was removed after the trial. Immediate postoperative mean VAS score was 1. This score stabilized 3 months after surgery. Patients with implanted stimulators reduced their pain medication dose by a mean of more than 50%. Three patients with facial weakness and sensory loss regained both strength and discriminative sensation during stimulation. In another patient, dysarthria improved. In a review of the literature, 29 (76%) of 38 patients with neuropathic facial pain treated with motor cortex stimulation achieved greater than 50% pain relief. CONCLUSION: These results provide further support for the use of motor cortex stimulation in facial neuropathic pain and document pain improvement as measured by multidimensional scales. Observations of motor and sensory improvements during stimulation suggest that stimulation alters cortical plasticity and inhibits thalamic hyperactivity.

Adult↗

PubMed2002

Effects of reversible cold block of face primary somatosensory cortex on orofacial movements and related face primary motor cortex neuronal activity.

Our previous studies have revealed that face primary somatosensory cortex (SI) as well as face primary motor cortex (MI) play important roles in the control of orofacial movements in awake monkeys, and that both face MI and face SI neurons may have an orofacial mechanoreceptive field and show activity related to orofacial movements. Since it is possible that the movement-related activity of face MI neurons could reflect movement-generated orofacial afferent inputs projecting to face MI via face SI, the present study used reversible cold block-induced inactivation of the monkey's face SI to determine if face MI neuronal activity related to a trained tongue-protrusion task, chewing or swallowing was dependent on the functional integrity of the ipsilateral face SI and if inactivation of face SI affects orofacial movements. The effects of face SI cold block were tested on chewing, swallowing and/or task-related activity of 73 face MI neurons. Both task and chewing and/or swallowing-related activity of most face MI neurons was independent of the functional integrity of the ipsilateral face SI since SI cold block affected the movement-related activity in approximately 25% of the neurons. Similarly, unilateral cold block of SI had very limited effects on the performance of the task and chewing, and no effect on the performance of swallowing. These findings suggest that movement-induced reafferentation via face SI may not be a significant factor in accounting for the activity of the majority of ipsilateral face MI neurons related to trained movements, chewing and swallowing.

Animals↗

PubMed2004

Hand movement distribution in the motor cortex: the influence of a concurrent task and motor imagery.

The aim of this work was to study the relevance of the primary motor cortex (M1) for motor functions different to the simple execution of motor orders. The M1 activity during the performance with individual fingers of a simple motor task (tonic flexion), a motor task that includes a complex motor computation but not motor execution (motor imagery), and a motor task that involves both the computation and execution of movements (phasic movement) was evaluated by functional magnetic resonance imaging (fMRI). The possible influence of other cortical tasks on the M1 activation induced by finger movements was assessed by evaluating the effect of a distracting concurrent task (numeric calculation). Data show that both the dimension of the area activated and the intensity of response were higher during motor planning than during motor execution. There is a mosaic-like distribution for motor-planning M1 functions, with the movement of individual fingers being controlled from several M1 loci. The concurrent mental-task induces a rapid functional reconfiguration of M1, adding M1 subsets to motor programming but excluding others. Present data support the involvement of the M1 in more than just simple motor execution, showing broader and more intense modifications during motor tasks not accompanied by movements (motor imagery) than during the execution of simple motor acts (tonic flexion).

Adult↗

PubMed2000

Motor cortex rules for learning and memory.

Primary motor cortex has a complex, interconnected anatomical and functional architecture with dynamic properties. Recent evidence suggests that, concomitantly with regulating muscle activity and movements, the motor cortex makes key contributions to learning and remembering motor skills.

Animals↗

PubMed1976

Anatomical analysis of ventrolateral thalamic input to primate motor cortex.

1. The origin and topographical organization of input to the arm area of the primate motor cortex from the ventrolateral thalamus were examined using the method of retrograde transport of horseradish peroxidase (HRP). 2. A thin, continuous slab of labeled neurons was found in the ventrolateral thalamus followingmultiple injections of HRP into the arm area of the motor cortex. The slab of labeled neurons was flanked, medially and laterally, by groups of unlabeled neurons. 3. The origin of ventrolateral thalamic input was more extensive than previously thought. Labeled neurons were found from A10.0 to A6.0 and occurred in three ventolateral thalamic subdivisions: ventralis lateralis pars oralis (VLo), ventralis lateralis pars caudalis (VLc), and ventralis posterior lateralis pars oralis (VPLo). For simplicity this region containing labeled neurons has been termed the ventrolateral thalamic (VL) arm area. 4. Injections of HRP into the somatic sensory cortex indicated that the thalamic regions which project to the somatic sensory cortex are separate from the VL arm area. 5. The distribution of labeled neurons following single injections of HRP into different regions of the motor cortex arm area indicated that the VL arm area is topographically organized, particularly its caudal part. Ventral regions of the VL arm area were labeled following HRP injections into motor cortex regions adjacent to the central sulcus where the representation of largely distal musculature is localized. Dorsal regions of the VL arm area were labeled following HRP injections into motor cortex regions more rostral to the central sulcus where the representation of more proximal musculature is localized. 6. A larger region of the VL arm area was labeled following HRP injections adjacent to the central sulcus than following the more rostral motor cortex injections. This suggests that, like the arm area of the motor cortex, more of the VL arm area is allotted to the representation of distal than proximal musculature. 7. Following very small cortical HRP injections, isolated labeled thalamic neurons were diffusely scattered throughout a 3-mm rostrocaudal extent of the VL arm area. In addition, a small focal cluster of labeled thalamic neurons was also seen. The labeled cluster was limited to 0.5 mm rostrocaudally and 300 mum in width. The focal distribution of labeled thalamic neurons suggests that aspects of a point to point organization may exist in the connection between VL and the motor cortex arm area.

Afferent Pathways↗

PubMed2006

Remodeling of synaptic structures in the motor cortex following spinal cord injury.

After spinal cord injury (SCI), structural reorganization occurs at multiple levels of the motor system including the motor cortex, and this remodeling may underlie recovery of motor function. The present study determined whether SCI leads to a remodeling of synaptic structures in the motor cortex. Dendritic spines in the rat motor cortex were visualized by confocal microscopy in fixed slices, and their density and morphology were analyzed after an overhemisection injury at C4 level. Spine density decreased at 7 days and partially recovered by 28 days. Spine head diameter significantly increased in a layer-specific manner. SCI led to a higher proportion of longer spines especially at 28 days, resulting in a roughly 10% increase in mean spine length. In addition, filopodium-like long dendritic protrusions were more frequently observed after SCI, suggesting an increase in synaptogenic events. This spine remodeling was accompanied by increased expression of polysialylated neural cell adhesion molecule, which attenuates adhesion between the pre- and postsynaptic membranes, in the motor cortex from as early as 3 days to 2 weeks after injury, suggesting a decrease in synaptic adhesion during the remodeling process. These results demonstrate time-dependent changes in spine density and morphology in the motor cortex following SCI. This synaptic remodeling seems to proceed with a time scale ranging from days to weeks. Elongation of dendritic spines may indicate a more immature and modifiable pattern of synaptic connectivity in the motor cortex being reorganized following SCI.

Amino Acids↗

PubMed2003

Motor cortex stimulation in patients with post-stroke pain: conscious somatosensory response and pain control.

We analyzed the conscious sensory responses to cortical stimulation of 31 patients with post-stroke pain who underwent motor cortex stimulation (MCS) therapy. During surgery for electrode placement, a sensory response (tingle projected to a localized peripheral area) was elicited by high-frequency stimulation (50 Hz) in 23 (84%) from the somatosensory cortex, and in 16 (52%) from the motor cortex without muscle contraction. Unpleasant painful sensation was induced or their original pain was exacerbated in 12 patients (39%) when the somatosensory cortex was stimulated and in two (6%) when the motor cortex was stimulated. Somatosensory responses were induced in eight (25%) even by low-frequency stimulation (1-2 Hz) of the motor cortex at an intensity below the threshold for muscle contraction. In contrast, among 20 nonpain patients who underwent a similar procedure for cortical mapping in epilepsy or brain tumor surgery, a sensory response was produced by high-frequency stimulation in only eight (40%; p < 0.02) from the somatosensory cortex and four (20%; p < 0.03) from the motor cortex. Pain sensation was not induced by stimulation of the somatosensory cortex (p < 0.002) or motor cortex in any of these patients. In addition, none of these patients reported a sensory response to low-frequency stimulation. In both of the two post-stroke pain patients who reported abnormal pain sensation in response to stimulation of the motor cortex, MCS failed to control their post-stroke pain. These findings imply that the sensitivity of the perceptual system even to activity of the motor cortex is heightened in post-stroke pain patients, which can sometimes hinder pain control by MCS.

Consciousness↗

PubMed1983

[Neuronal correlates of the motor function of the cerebral motor cortex].

Modern ideas about the motor cortex neuronal mechanisms ensuring the initiation and correction of the instrumental manipulational movements in mammals have been analysed. A close correlation has been established to exist between the neuronal activity and various characteristics of movement including those that are not induced by muscle force. The role of somatic afferentation in the formation and realization of the movement programme is analysed as well as in motor output modulation by means of fast feedback.

Afferent Pathways↗

PubMedDate not supplied

Motor cortex stimulation in the treatment of central and neuropathic pain.

BACKGROUND: Motor cortex stimulation has been proposed for the treatment of central pain. METHODS: Thirty-two patients with refractory central and neuropathic pain of peripheral origin were treated by chronic stimulation of the motor cortex between May 1993 and January 1997. The mean follow-up was 27.3 months. The first 24 patients were operated on according to the technique described by Tsubokawa. The last 13 cases (8 new patients and 5 reinterventions) were operated on by a technique including localization by superficial CT reconstruction of the central region and neuronavigator guidance. The position of the central sulcus was confirmed by the use of intraoperative somatosensory evoked potentials. The somatotopic organization of the motor cortex was established preoperatively by studying the motor responses at stimulation of the motor cortex through the dura. RESULTS: Ten of the 13 patients with central pain (77%) and 10 of the 12 patients with neuropathic facial pain experienced substantial pain relief (83.3%). One of the three patients with post-paraplegia pain was clearly improved. A satisfactory result was obtained in one patient with pain related to plexus avulsion and in one patient with pain related to intercostal herpes zoster. None of the patients developed epileptic seizures. CONCLUSIONS: Our results confirm that chronic stimulation of the motor cortex is an effective method in treating certain forms of refractory pain.

Adult↗

PubMed1988

[Effect of the microiontophoretic feed of acetylcholine and noradrenaline on the neuronal reactivity of the motor cortex to specific stimuli].

In the forelimb area of the motor cortex after microiontophoretic injection of acetylcholine a group of nervous cells revealed more rapid, more stable and more effective reactions to afferent stimuli. The interrelation of impulsive activity of some of these neurons and electromyographic activity of forelimb muscles has given a possibility to propose that acetylcholine mobilizes the motor cortex for motor function regulations. The only result of noradrenaline application to motor cortex neurons was the prolongation of their responses to specific afferent stimulation.

Acetylcholine↗

PubMed2000

Transcranial magnetic stimulation of primary motor cortex affects mental rotation.

Neuroimaging studies have shown that motor structures are activated not only during overt motor behavior but also during tasks that require no overt motor behavior, such as motor imagery and mental rotation. We tested the hypothesis that activation of the primary motor cortex is needed for mental rotation by using single- pulse transcranial magnetic stimulation (TMS). Single-pulse TMS was delivered to the representation of the hand in left primary motor cortex while participants performed mental rotation of pictures of hands and feet. Relative to a peripheral magnetic stimulation control condition, response times (RTs) were slower when TMS was delivered at 650 ms but not at 400 ms after stimulus onset. The magnetic stimulation effect at 650 ms was larger for hands than for feet. These findings demonstrate that (i) activation of the left primary motor cortex has a causal role in the mental rotation of pictures of hands; (ii) this role is stimulus-specific because disruption of neural activity in the hand area slowed RTs for pictures of hands more than feet; and (iii) left primary motor cortex is involved relatively late in the mental rotation process.

Adult↗