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Results for “Motor Cortex”

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PubMed1995

Afferent excitation of human motor cortex as revealed by enhancement of direct cortico-spinal actions on motoneurones.

Changes in motor cortex excitability induced by somatosensory afferences were evaluated in 5 subjects by testing how the short-latency cortico-spinal effects evoked by transcranial magnetic stimulation in flexor carpi radialis (FCR) motoneurones were influenced by volleys in median nerve afferent fibres. Transcranial magnetic stimulation induced two facilitatory peaks on FCR H reflex, the first at a conditioning-test interval of about -3 msec and the second at msec, separated by a phase of inhibition. If an electric shock to the median nerve at the wrist, 0.8-1 x motor threshold (MT) for thenar muscles, preceded the cortical stimulus by 18-25 msec, an increase in size of both facilitatory peaks was observed. The increase was partly due to a direct action of the median nerve volley on motoneurones. When this contribution was subtracted, two peaks of additional facilitation resulted as the effect of combined conditioning. Additional facilitation was present even during the short-lasting phase ascribed to monosynaptic cortico-spinal excitation of motoneurones, i.e., the first millisecond of the earliest facilitatory peak. This result indicates that cortical responsiveness to magnetic stimulation had been enhanced by the peripheral stimulus. The time course of the excitability changes in motor cortex was compared with the cortical somatosensory evoked potentials (SEPs) induced by the same peripheral stimulus. Additional facilitation was present immediately after the N20 peak of SEPs and lasted 8-10 msec. Additional facilitation had the same threshold as N20 (0.6 x MT) and grew in parallel with it when grading the afferent stimulus up to 1 MT.

Afferent Pathways↗

PubMed2006

Possible origins of the complex topographic organization of motor cortex: reduction of a multidimensional space onto a two-dimensional array.

We propose that some of the features of the topographic organization in motor cortex emerge from a competition among several conflicting mapping requisites. These competing requisites include a somatotopic map of the body, a map of hand location in space, and a partitioning of cortex into regions that emphasize different complex, ethologically relevant movements. No one type of map fully explains the topography; instead, all three influences (and perhaps others untested here) interact to form the topography. A standard algorithm (Kohonen network) was used to generate an artificial motor cortex array that optimized local continuity for these conflicting mapping requisites. The resultant hybrid map contained many features seen in actual motor cortex, including the following: a rough, overlapping somatotopy; a posterior strip in which simpler movements were represented and more somatotopic segregation was observed, and an anterior strip in which more complex, multisegmental movements were represented and the somatotopy was less segregated; a clustering of different complex, multisegmental movements into specific subregions of cortex that resembled the arrangement of subregions found in the monkey; three hand representations arranged on the cortex in a manner similar to the primary motor, dorsal premotor, and ventral premotor hand areas in the monkey; and maps of hand location that approximately matched the maps observed in the monkey.

Algorithms↗

PubMed1995

Functional recovery of forelimb response capacity after forelimb primary motor cortex damage in the rat is due to the reorganization of adjacent areas of cortex.

Functional recovery after brain damage has been described frequently and different mechanisms have been proposed to account for the observed recovery. One possible mechanism involves the capacity of one part of the brain to take over the function of another. A possible area for this to take place is in the cerebral cortex, where a variety of reorganizational processes have been described after different manipulations. We show in the present study that the forelimb force and response capacity of the rat, which becomes highly impaired after the bilateral ablation of the forelimb primary motor cortex, is recovered when the animals receive an electrical stimulation in the ventral tegmental nucleus contingent to each forelimb response in the task. Microstimulation mapping of the cortical areas adjacent to the forelimb primary motor cortex revealed the appearance of an area located caudolaterally to the forelimb primary motor cortex, where forelimb movements could be evoked in recovered animals but to a lesser extent in non-recovered animals. A positive and significant correlation was observed between the size of the reorganized forelimb area and the behavioral performance of the animals. Ablation of the forelimb reorganized area in recovered animals reinstated the forelimb behavioral impairment, while the same lesion in normal animals had no effect on the behavioral performance. The results indicate that recovery after bilateral forelimb primary motor cortex ablation may be due to the organization of specific adjacent areas in the cortex.

Animals↗

PubMed2003

Further experience with extradural motor cortex stimulation for treatment of advanced Parkinson's disease. Report of 3 new cases.

AIM: To report the results obtained with the extradural motor cortex stimulation in Parkinson's disease. METHODS: Three patients were submitted to MRI images and functional MRI in order to identify the upper limb motor area. Then a quadripolar electrostimulator was introduced in the extradural space, through 2 burr holes. RESULTS: Unilateral, extradural motor cortex stimulation relieves, at least partially, but sometime dramatically, the whole spectrum of symptoms in advanced Parkinson disease: tremor and rigor bilaterally in all limbs; akinesia; standing, anteropulsion, gait; motor performance; dysphagia; speech and swallowing. Also the symptoms of long term dopa syndrome--dyskinesias, and other secondary effect of L-dopa administration, psychiatric symptoms--are improved. CONCLUSION: The results seems do not fade away with time. Drug dosage may be reduced by 50%. We suggest early employ of transdural motor cortex stimulation.

Aged↗

PubMed1982

Thalamic afferents to the motor cortex in the cat. A horseradish peroxidase study.

Thalamic projections to the motor cortex have been studied in the cat by injecting small amounts of horseradish peroxidase in different parts of areas 4 and 6. The nuclei which more abundantly project to the motor cortex are the ventral anterior-ventral lateral complex, the ventral medial and the posterior complex. These projections are topographically organized. Other projections arise from the ventral postero-lateral, ventral postero-inferior, central lateral, central medial, medial dorsal, lateral posterior-pulvinar, suprageniculate and centrum medianum-parafascicular nuclei.

Afferent Pathways↗

PubMed2006

Skill representation in the primary motor cortex after long-term practice.

The acquisition of motor skills can lead to profound changes in the functional organization of the primary motor cortex (M1). For example, performance of movement sequences after prolonged practice is associated with an expansion of the effector representation in M1. Paradoxically, there is little evidence that the activity of M1 neurons reflects acquired skills, especially sequences of movements. We examined the activity of M1 neurons during skilled movement sequences in macaques trained to successively hit targets on a monitor. The targets appeared either pseudorandomly (Random mode) or in one of two repeating sequences (Repeating mode). With practice, response times for repeating sequences substantially declined and the monkeys performed the task predictively. Highly trained animals retained the acquired skill after long gaps in practice. After >2 yr of training, 40% of M1 neurons were differentially active during the two task modes. Variations in movement kinematics did not fully explain the task-dependent modulation of neuron activity. Differentially active neurons were more strongly influenced by task mode than by kinematics. Our results suggest that practice sculpts the response properties of M1 neurons. M1 may be a site of storage for the internal representation of skilled sequential movements.

Animals↗

PubMed2006

Linear encoding of muscle activity in primary motor cortex and cerebellum.

The activity of neurons in primary motor cortex (M1) and cerebellum is known to correlate with extrinsic movement parameters, including hand position and velocity. Relatively few studies have addressed the encoding of intrinsic parameters, such as muscle activity. Here we applied a generalized regression analysis to describe the relationship of neurons in M1 and cerebellar dentate nucleus to electromyographic (EMG) activity from hand and forearm muscles, during performance of precision grip by macaque monkeys. We showed that cells in both M1 and dentate encode muscle activity in a linear fashion, and that EMG signals provide predictions of neural discharge that are equally accurate to those from kinematic information under these task conditions. Neural activity in M1 was significantly more correlated with both EMG and kinematic signals than was activity in dentate nucleus. Furthermore, the analysis enabled us to look at the temporal properties of muscle encoding. Cells were broadly tuned to muscle activity as a function of the lag between spiking and EMG and there was considerable heterogeneity in the optimal delay among individual neurons. However, a single lag (40 ms) was generally sufficient to provide good fits. Finally, incorporating spike history effects in our model offered no advantage in predicting novel spike trains, reinforcing the simple nature of the muscle encoding that we observed here.

Algorithms↗

PubMed1996

Cholinergic modulation of synaptic transmission in horizontal connections of rat motor cortex.

The influence of compounds interacting with cholinergic systems on field potentials evoked in layer II/III horizontal connections was investigated in rat motor cortex in vitro. The cholinesterase inhibitor eserine (10 microM) decreased field responses by 20 +/- 2%. This effect could be prevented by preincubation with atropine (10 microM). Application of 5 microM carbachol resulted in reduction of the responses by 30 +/- 1%. These reductions were reversible, repeatable and independent of stimulus intensity; they could be blocked by the M1 muscarinic receptor antagonist pirenzepine (3 microM) but not by the M2 muscarinic receptor antagonist gallamine (10 microM). During carbachol application, paired-pulse facilitation (40 ms interpulse interval) was increased. The results indicate that endogenous acetylcholine may modulate excitatory synaptic transmission in horizontal connections of rat motor cortex, most likely by acting upon M1 receptors located presynaptically on glutamatergic terminals, and may contribute both to information processing and synaptic plasticity within the motor cortex.

Animals↗

PubMed1984

Unit activity of motor cortex during acoustically signalled reaching in rats.

Changes of unit activity, accompanying a discriminated instrumental reaction were studied in the motor cortex of rats (n = 15) trained to reach into a narrow tubular feeder for food pellets. A shutter opened the feeder for 1280 ms while the presence of food was signalled by 600 Hz (CS+) tone and its absence by a 3000 Hz (CS-) tone. The electrophysiological experiments were performed after the rats had developed a preference for reaching with the left or right forepaw and when their discriminations were 75% correct. Unit activity was recorded in the motor cortex contralateral to the preferred forepaw using capillary microelectrodes and a head-mounted microdrive. Post-stimulus histograms (PSHs) to CS+ (n = 71) showed an increase of firing rate in the first 120 ms after CS onset (40% units) and a tonic excitation (55% units) starting some 200 ms later. The second component was related to movement as revealed by simultaneously plotted peri-reach histograms. The first component was related to preparatory activity and was also present in the PSHs obtained during correct reactions to CS- (n = 29). Then, absence of reaching was manifested by inhibition replacing the second excitatory component. The first but not the second excitatory components were seen in the PSHs plotted during negative reactions to CS+ (n = 18). It is concluded that the conditioned stimuli elicit in the motor cortex preparatory activity preceding actual movement by 200-250 ms. The neuronal populations engaged in the preparatory activity and movement execution overlap.

Acoustic Stimulation↗

PubMedDate not supplied

Static versus dynamic effects in motor cortex and area 5: comparison during movement time.

We examined the directionality of static and dynamic motor effects on cell discharge recorded during arm movements in motor cortex and area 5. Movements of 8 directions were performed by rhesus monkeys in a two-dimensional space ('movement task'). Static effects were determined using a static hold task in the same workspace ('static task'); they were adequately described as planar activity surfaces in 78/124 (63%) and 63/105 (60%) of motor cortical and area 5 cells, respectively, that showed statistically significant changes in steady-state activity associated with holding in different positions. The frequency of discharge expected during the movement time on the basis of the static effect alone was calculated for every trial using the static plane equation and the movement path. The difference between this value and the discharge rate observed in the movement task during the same period of time was taken as an estimate of the contribution of non-static, i.e. dynamic factors. Thus static and dynamic tuning curves were generated. These curves were compared with respect to depth of tuning and spatial congruence. The former was estimated by taking the difference between the maximum and minimum of the curve, and the latter by measuring the correlation between the static and dynamic curves. We found the following. First, the dynamic tuning curves were more deeply tuned than the corresponding static ones, by 1.51 and 1.59 times in motor cortex and area 5, respectively. This result was statistically significant in both areas (paired t-test, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1998

Neural activity related to reaching and grasping in rostral and caudal regions of rat motor cortex.

The objective of this study was to assess the relation of motor cortical neural activity in the rat to self-paced reach-to-grasp movements. Overall, around 40% of excitatory and 60% of inhibitory modulations in neuronal activity began prior to reach onset. These data are consistent with a role for rat motor cortex in the initiation and control of the reaching movement. In addition, although the reach only lasted a short time, 30% of excitations and inhibitions began while it was in progress. The existence of such modulations occurring during the reach is consistent with previous data showing activity of cortical neurons late in the reach, and suggests a heavy involvement of cortical neurons in controlling the recently described, complex movements associated with grasping that are seen in the rat. These features were broadly similar in neurones from both the caudal and rostral subdivisions of rat motor cortex.

Action Potentials↗

PubMed2006

Associative plasticity in human motor cortex during voluntary muscle contraction.

TMS pulses over the hand area of motor cortex activate different subpopulations of synaptic connections if the direction of the induced current in the brain is reversed from posterior-anterior (PA) direction to anterior-posterior (AP). We tested whether this also made a difference to the after-effects of paired associative stimulation (PAS: ulnar nerve stimulation followed 25 ms later by a transcranial magnetic stimulation pulse). If 50 pairs of stimuli (0.1 Hz) were applied using conventional suprathreshold PA-PAS in resting subjects, there was no effect on motor-evoked potentials (MEPs) in the first dorsal interosseous muscle. In contrast if the same number of pulses were given while subjects made a small tonic (5% maximum) contraction, MEPs were facilitated and resting motor threshold reduced when AP but not PA pulses were used. Subsequent experiments employed subthreshold TMS (95% of the active motor threshold) during voluntary muscle contraction. MEP facilitation accompanied by reduced AP threshold occurred when PAS was given using AP pulses (AP-Sub-PAS), whereas PAS using PA pulses (PA-Sub-PAS) had no excitatory effect. There was no facilitation if the ulnar nerve stimulus was replaced by digital nerve stimulation. There was a tendency for short interval intracortical inhibition (SICI) to decrease and intracortical facilitation (ICF) to increase after AP-Sub-PAS. We propose that the increased effectiveness of AP-Sub-PAS over PA-Sub-PAS is due to the fact that AP TMS more readily activates I3 inputs to corticospinal neurons and hence that these are an important component of associative plasticity in the human motor cortex.

Adult↗

PubMed2002

Dual modulating effects of amphetamine on neuronal excitability and stimulation-induced plasticity in human motor cortex.

OBJECTIVES: The objective of the present study is to test the modulating effects of dextro-amphetamine (d-AMP) on excitability and stimulation-induced plasticity in human motor cortex. METHODS: Transcranial magnetic stimulation (TMS) was used to measure motor threshold, motor evoked potential (MEP) size and paired-pulse intracortical facilitation (ICF) in the biceps muscle of 7 healthy subjects before and after two different experimental manipulations: temporary forearm ischemic nerve block (INB) alone, or INB plus 0.1 Hz repetitive TMS (INB+rTMS) of the motor cortex contralateral to INB. Both manipulations were run after treatment with 10mg of d-AMP or placebo (PBO). RESULTS: In the PBO experiments, INB alone had no significant effect on MEP size or ICF, while INB+rTMS produced long-lasting (>60 min) increases. Compared with PBO, d-AMP led to a short-lasting ( approximately 10 min) increase in MEP size in the INB alone experiment, but suppressed the long-lasting increases of MEP size and ICF in the INB+rTMS experiment. CONCLUSIONS: The present findings suggest that d-AMP increases neuronal excitability but suppresses long-lasting stimulation-induced plasticity in human motor cortex. These dual effects may be relevant when using d-AMP to modulate human cortex function.

Adult↗

PubMed1999

Intraoperative validation of functional magnetic resonance imaging and cortical reorganization patterns in patients with brain tumors involving the primary motor cortex.

OBJECT: The purpose of the present study was to compare the results of functional magnetic resonance (fMR) imaging with those of intraoperative cortical stimulation in patients who harbored tumors close to or involving the primary motor area and to assess the usefulness of fMR imaging in the objective evaluation of motor function as part of the surgical strategy in the treatment of these patients. METHODS: A total of 11 consecutive patients, whose tumors were close to or involving the central region, underwent presurgical blood oxygen level-dependent fMR imaging while performing a motor paradigm that required them to clench and spread their hands contra- and ipsilateral to the tumor. Statistical cross-correlation functional maps covering the primary and secondary motor cortical areas were generated and overlaid onto high-resolution anatomical MR images. Intraoperative electrical cortical stimulation was performed to validate the presurgical fMR imaging findings. In nine (82%) of 11 patients, the anatomical fMR imaging localization of motor areas could be verified by intraoperative electrical cortical stimulation. In seven patients two or more activation sites were demonstrated on fMR imaging, which were considered a consequence of reorganization phenomena of the motor cortex: contralateral primary motor area (nine patients), contralateral premotor area (four patients), ipsilateral primary motor area (two patients), and ipsilateral premotor area (four patients). CONCLUSIONS: Functional MR imaging can be used to perform objective evaluation of motor function and surgical planning in patients who harbor lesions near or involving the primary motor cortex. Correlation between fMR imaging findings and the results of direct electrical brain stimulation is high, although not 100%. Based on their study, the authors believe that cortical reorganization patterns of motor areas might explain the differences in motor function and the diversity of postoperative motor function among patients with central tumors.

Adult↗

PubMed2002

Temporal relation of population activity in visual areas MT/MST and in primary motor cortex during visually guided tracking movements.

There is growing evidence that in primate cerebral cortex the areas along the 'dorsal pathway' are involved in the transformation of visual motion information towards a motor command. To pursue this cortical flow of information from visual motion areas to the motor cortex, single-cell activity was recorded from visual areas MT/MST (middle temporal area/medial superior temporal area) and from primary motor cortex (M1) while monkeys tracked moving targets with their right hand. Spike activity of 353 directionally tuned motor cortex cells was combined to a time-varying population vector, and similarly a time-resolved visual population vector was calculated from 252 MT/MST cells. Both population vectors code faithfully for the direction of the collinear motion of target and hand. For a given direction, the length of the population vectors varied over time during the performance of the task. The temporal evolution of both population responses reflects the different relationship between the early visual responses to the moving target and the directional motor command controlling the hand movement. The results indicate that during the visual tracking task visual and motor populations which code for similar directions of movement are co-activated with considerable temporal overlap. Despite this co-activation in both modalities, we failed to observe any significant synchronization between areas MT/MST and M1.

Animals↗

PubMed2007

Extradural motor cortex stimulation in Parkinson's disease.

Extradural motor cortex stimulation (EMCS) is a surgical procedure proposed for patients with advanced Parkinson's disease (PD) who cannot undergo deep brain stimulation (DBS). Five PD patients with motor fluctuations and dyskinesia underwent EMCS of the left hemisphere. All fulfilled CAPSIT criteria for DBS, with the exception of age > 70 years. Patients were assessed preoperatively and 6 months after surgery on and off medications, with stimulator on, and 2 weeks later with stimulator off. Outcome measures included changes in mean medication dosage (levodopa and dopamine agonists), Unified Parkinson's Disease Rating Scale (UPDRS Parts II-III and Item 39), and dyskinesias (Abnormal Involuntary Movements Scale [AIMS]). We found no significant mean changes following EMCS. However, there was a trend for a reduction of mean daily medication intake (-30%) and AIMS (-19%). There were 3 patients who reported reduced OFF time (UPDRS Item 39) and 4 of 5 who felt a subjective benefit in stability and gait. In our PD cohort, EMCS induced no objective benefit, although some subjective improvement was reported mostly on axial symptoms.

Aged↗

PubMed2003

Twitches versus movements: a story of motor cortex.

Modern study of the neurophysiology of the cerebral cortex began with Fritsch and Hitzig's discovery that electrical stimulation of the cortex produces movements. The importance of this discovery was threefold: it was the first demonstration of cortex devoted to motor function, the first indication that the cortex was electrically excitable, and the first evidence of a topographically organized representation in the brain. Fritsch and Hitzig's basic findings were soon replicated by Ferrier, but there were differences between the two studies in both method and interpretation. These different approaches have continued to reverberate in research on the function of motor cortex from the late 19th century to the present day.

Animals↗

PubMed1998

Interictal inhibitory mechanisms in patients with cryptogenic motor cortex epilepsy: a study of the silent period following transcranial magnetic stimulation.

The silent period (SP) following transcranial magnetic stimulation (TMS) of the motor cortex is mainly due to cortical inhibitory mechanisms. The aim of the present study was to investigate these inhibitory phenomena in primary motor cortex epilepsy. We studied the TMS-induced SP in both the first dorsal interosseous (FDI) muscles in 8 patients who suffered from cryptogenic partial epilepsy with seizures starting with clonic movements of the right upper limb. All patients were on chronic medication with antiepileptic drugs. Therefore, besides contrasting the results with 16 age-matched normal controls, we also studied 10 patients receiving similar antiepileptic treatments who suffered from cryptogenic partial epilepsy with seizures characterised by the absence of clonic manifestations. The duration of the SP was bilaterally increased in the patients with clonic seizures when compared with the two other groups of subjects. The SP was longer in the left FDI muscle (contralateral to the side of the clonic manifestation in all the patients). Our findings likely indicate enhanced interictal inhibitory mechanisms in patients with partial epilepsy involving the primary motor cortex. The resulting inhibitory effect could be greater in the intact hemisphere rather than in the affected one, in which the hyperexcitability of the epileptic focus had to be counterbalanced.

Adolescent↗