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PubMed2005

Motor but not sensory representation in motor cortex depends on postsynaptic activity during development and in maturity.

The movement representation in the primary motor cortex (M1) of the cat develops between postnatal weeks 7-12. The somatosensory representation in motor cortex is present by the age that the motor map begins to develop. In this study we examined the role of neural activity in development and maintenance of the M1 movement and somatosensory representations. We blocked activity of M1 neurons unilaterally for one month by intracortical infusion of the GABA agonist muscimol during the motor map development period in kittens and in mature cats. After the drug effects were no longer present, we used microstimulation and multiunit recording in the forelimb areas of M1 to determine the motor and somatosensory representations in the infused and noninfused sides. In both kittens and adults, there was a severe reduction or elimination of sites where microstimulation evoked a motor response in the inactivated compared with the control side. In contrast, there was no difference in the percentage, topography or receptive field modality of sites receiving somatosensory inputs on the inactivated and control sides. Moreover, the pattern of somatosensory input to M1 was similar before and after inactivation. This suggests that somatosensory input to M1 is stable after the connections initially develop. Since activity blockade had the same effects on the motor representation of kittens and adult cats, M1 neuronal activity, while possibly important in map development, is equally necessary for map maintenance.

Adaptation, Physiological↗

PubMed2005

The motor cortex is involved in reflexive compensatory adjustment of speech articulation.

Although speech articulation relies heavily on the sensorimotor processing, little is known about its brain control mechanisms. Here, we investigate, using transcranial magnetic stimulation, whether the motor cortex contributes to the generation of quick sensorimotor responses involved in speech motor coordination. By applying a jaw-lowering perturbation, we induced a reflexive compensatory upper-lip response, which assists in maintaining the intact labial aperture in the production of bilabial fricative consonants. This reflex response was significantly facilitated by subthreshold transcranial magnetic stimulation over the motor cortex, whereas a simple perioral reflex that is mediated only within the brainstem was not. This suggests that the motor cortex is involved in generating this functional reflexive articulatory compensation.

Electric Stimulation↗

PubMed2005

Contribution of the motor cortex to the structure and the timing of hindlimb locomotion in the cat: a microstimulation study.

We used microstimulation to examine the contribution of the motor cortex to the structure and timing of the hindlimb step cycle during locomotion in the intact cat. Stimulation was applied to the hindlimb representation of the motor cortex in 34 sites in three cats using either standard glass-insulated microelectrodes (16 sites in 1 cat) or chronically implanted microwire electrodes (18 sites in 2 cats). Stimulation at just suprathreshold intensities with the cat at rest produced multi-joint movements at a majority of sites (21/34, 62%) but evoked responses restricted to a single joint, normally the ankle, at the other 13/34 (38%) sites. Stimulation during locomotion generally evoked larger responses than the same stimulation at rest and frequently activated additional muscles. Stimulation at all 34 sites evoked phase-dependent responses in which stimulation in swing produced transient increases in activity in flexor muscles while stimulation during stance produced transient decreases in activity in extensors. Stimulation with long (200 ms) trains of stimuli in swing produced an increased level of activity and duration of flexor muscles without producing changes in cycle duration. In contrast, stimulation during stance decreased the duration of the extensor muscle activity and initiated a new and premature period of swing, resetting the step cycle. Stimulation of the pyramidal tract in two of these three cats as well as in two additional ones produced similar effects. The results show that the motor cortex is capable of influencing hindlimb activity during locomotion in a similar manner to that seen for the forelimb.

Animals↗

PubMed1987

Some experiences of techniques for stimulation of the human cerebral motor cortex through the scalp.

Stimulation of the motor cortex transcranially has shown a rough somatotopy of stimulation sites on the scalp corresponding to the homunculus and preferential activation of contralateral hand muscles, as well as very short latencies of signals in the cervical spinal cord. The responses are also facilitated by background activation of the muscles. We are reporting a set of patients studied using electrical and magnetic stimulation transcranially. We observed that the latency of electromyogram activation is much shorter in active than contracting muscles and that the muscle twitch produced by cortical stimulation can exceed the force produced by supramaximal stimulation of the peripheral nerve. Our findings suggest that this may be due to multiple firing of motor neurons. Another observation is that magnetic stimulation is not as subject to a reduction in the response latency with facilitation, and response latencies with magnetic stimulation were 2 ms longer than with electrical stimulation. The implications of these findings are discussed.

Adult↗

PubMed1996

The excitability of the human motor cortex increases during execution and mental imagination of sequential but not repetitive finger movements.

Motor potentials (MEPs) evoked by focal (figure-of-eight coil) transcranial magnetic stimulation of the left motor cortex were recorded from the right opponens pollicis (OP) and flexor digitorum superficialis (FDS) of 14 normal subjects during different motor tasks. Changes in motor cortical excitability under behavioural conditions presumably connected with premotor and supplementary motor area (SMA) activation were investigated by comparing the size of the MEPs obtained during: (1) rest, (2) mental calculus, (3) repetitive left thumb-to-index opposition, (4) mental simulation of the same task with the right hand, (5) sequences of left thumb-to-fingers opposition, and (6) mental simulation of the same sequences with the right hand. MEP size significantly increased in both muscles during sequential movements of the left hand and sequence simulation with the right hand, but not during mental calculus or actual or simulated repetitive movements. The H-reflex evoked in the OP and FDS muscles by electrical stimulation of the median nerve (at wrist and elbow, respectively) under the same experimental conditions did not show significant modifications. The increase in MEP size during non-routine actual or imagined sequences of finger movements supports the view that the SMA is activated under these conditions and that it exerts a direct facilitatory influence on the motor cortex.

Adult↗

PubMed1997

Role of the ipsilateral motor cortex in voluntary movement.

The ipsilateral primary motor cortex (M1) plays a role in voluntary movement. In our studies, we used repetitive transcranial magnetic stimulation (rTMS) to study the effects of transient disruption of the ipsilateral M1 on the performance of finger sequences in right-handed normal subjects. Stimulation of the M1 ipsilateral to the movement induced timing errors in both simple and complex sequences performed with either hand, but with complex sequences, the effects were more pronounced with the left-sided stimulation. Recent studies in both animals and humans have confirmed the traditional view that ipsilateral projections from M1 to the upper limb are mainly directed to truncal and proximal muscles, with little evidence for direct connections to distal muscles. The ipsilateral motor pathway appears to be an important mechanism for functional recovery after focal brain injury during infancy, but its role in functional recovery for older children and adults has not yet been clearly demonstrated. There is increasing evidence from studies using different methodologies such as rTMS, functional imaging and movement-related cortical potentials, that M1 is involved in ipsilateral hand movements, with greater involvement in more complex tasks and the left hemisphere playing a greater role than the right.

Adult↗

PubMed2003

Inference of hand movements from local field potentials in monkey motor cortex.

The spiking of neuronal populations in motor cortex provides accurate information about movement parameters. Here we show that hand movement target and velocity can be inferred from multiple local field potentials (LFPs) in single trials approximately as efficiently as from multiple single-unit activity (SUA) recorded from the same electrodes. Our results indicate that LFPs can be used as an additional signal for decoding brain activity, particularly for new neuroprosthetic applications.

Action Potentials↗

PubMed1994

Inhibitory actions of motor cortex following unilateral brain lesions as studied by magnetic brain stimulation.

Noninvasive transcranial magnetic stimulation (TMS) of the motor cortex not only induces short-latency, motor-evoked potentials (MEP) in contralateral muscles, but also inhibitory phenomena. One type of inhibitory action appears directly after the MEP in contralateral muscles and can be visualized by blockade of tonic, voluntary electromyographic (EMG) activity (postexcitatory inhibition, PI). Evidence for a cortical origin of PI, especially in its later part, was derived from double cortical stimulation in previous studies and is further supported by examination of PI in patients with focal hemispheric unilateral brain lesions in the present study. Thirty patients with different sites of vascular or tumour lesions were studied by TMS. In 6 patients with circumscribed lesions of the primary sensorimotor cortex a significant shortening of PI to contralateral muscles was observed. In 7 patients with focal lesions of the thalamus or internal capsule, in 6 patients with lesions of the premotor cortex and in 5 patients with lesions restricted to the parietal or temporal lobe, a significant prolongation of PI to the contralateral muscles was detected. Six patients with transient ischemic attacks showed either prolongation or shortening of PI. We conclude that PI is predominantly generated in the primary motor cortex, correspondingly its damage causes shortening of PI. In contrast, damage to brain areas that project to the primary motor cortex is followed by prolongation of PI. This remote effect on the primary motor cortex may result from disinhibition of cortical interneurones.

Adult↗

PubMed1992

Interhemispheric inhibition of the human motor cortex.

1. Using two magnetic stimulators, we investigated the effect of a conditioning magnetic stimulus over the motor cortex of one hemisphere on the size of EMG responses evoked in the first dorsal interosseous (FDI) muscle by a magnetic test stimulus given over the opposite hemisphere. 2. A single conditioning shock to one hemisphere produced inhibition of the test response evoked from the opposite hemisphere when the conditioning-test interval was 5-6 ms or longer. We shall refer to this as interhemispheric inhibition. However, the minimum latency of inhibition observed using surface EMG responses may have underestimated the true interhemispheric conduction time. Single motor unit studies suggested values 4-7 ms longer than the minimum interval observed with surface EMG. 3. Interhemispheric inhibition was seen when the test muscle was active or relaxed. Increasing the intensity of the conditioning stimulus increased the duration of inhibition: increasing the intensity of the test stimulus reduced the depth of inhibition. 4. The conditioning coil had to be placed on the appropriate area of scalp for inhibition to occur. The effect of the conditioning stimulus was maximal when it was applied over the hand area of motor cortex, and decreased when the stimulus was moved medial or lateral to that point. 5. The inhibitory effect on the test stimulus probably occurred at the level of the cerebral cortex. In contrast to the inhibition of test responses evoked by magnetic test stimuli, test responses evoked in active FDI by a small anodal electric shock were not significantly inhibited by a contralateral magnetic conditioning stimulus. Similarly, H reflexes in relaxed forearm flexor muscles were unaffected by conditioning stimuli to the ipsilateral hemisphere. However, inhibition was observed if the experiment was repeated with the muscles active.

Adult↗

PubMed2003

Whisker motor cortex ablation and whisker movement patterns.

Previous studies, based on qualitative observations, reported that lesions of the whisker motor cortex produce no deficits in whisking behavior. We used high-resolution optoelectronic recording methods to compare the temporal organization and kinematics of whisker movements before and after unilateral lesions of whisker motor cortex in rats. We now report that while the lesion did not abolish whisking, it significantly disrupted whisking kinematics, coordination, and temporal organization. Lesioned animals showed significant increases in the velocity and amplitude of whisker protractions contralateral to the lesions, as well as a reduction in the synchrony of whisker movements on the two sides of the face. There was a marked shift in the distribution of whisking frequencies, with reduction of activity in the 5-7 Hz bandwidth and increased activity at < 2 Hz. Disruptions of the normal whisking pattern were evident on both sides of the face, and the magnitude of these effects was proportional to the extent of the cortical ablation. We suggest that the observed deficits reflect an imbalance in cortical inputs to a brainstem central pattern generator.

Animals↗

PubMed1998

Inhibitory influence of the ipsilateral motor cortex on responses to stimulation of the human cortex and pyramidal tract.

1. The ability of the primary motor cortex (M1) to modulate motor responses in ipsilateral hand muscles seems to be important for normal motor control and potentially also for recovery after brain lesions. It is not clear which pathways mediate this ipsilateral modulation. Transcallosal connections have been proposed, but are known to be sparse between cortical hand motor representations in primates. The present study was performed to determine whether descending ipsilateral modulation of motor responses might also be mediated below the cortical level in humans. 2. A paired-pulse protocol was used, in which motor-evoked potentials (MEPs) were produced by cortical transcranial magnetic stimulation (cTMS) or by electrical stimulation of the pyramidal tract at the level of the pyramidal decussation (pdTES), in both preactivated and relaxed hand muscles. Paired stimuli were applied at various interstimulus intervals (ISIs) between 2 and 100 ms. The conditioning stimulus (CS) was always magnetic, and delivered to the M1 ipsilateral to the target hand, prior to the test stimulus (TS). The magnetic TS was delivered to the M1 contralateral to the target hand; the electrical TS was applied through electrodes placed over the mastoid process bilaterally. Further experiments included cortical electrical stimulation and H-reflexes. The MEP amplitudes were averaged separately for each ISI and the control condition (no CS), and expressed as a percentage of the unconditioned response. 3. Conditioning stimulation of the ipsilateral M1 resulted in significant inhibition of magnetically evoked MEPs, and also of MEPs produced by pdTES. Inhibition occurred at ISIs between 6 and 50 ms, and was observed in preactivated and relaxed muscles. Higher CS intensities caused greater inhibition of both cTMS- and pdTES-evoked MEPs. 4. While the conditioning effects on magnetically evoked muscle responses could be explained by a transcallosal mechanism, the effects on pdTES-evoked MEPs cannot, because they are elicited subcortically and are therefore not susceptible to inhibitory mechanisms transmitted at the cortico-cortical level. 5. In conclusion, the present results provide novel evidence that the inhibitory influence of the human M1 on ipsilateral hand muscles is to a significant extent mediated below the cortical level, and not only through cortico-cortical transcallosal connections. They point to a concept of inhibitory interaction between the two primary motor cortices that is relayed at multiple levels along the neuroaxis, thus perhaps providing a structurally redundant system which may become important in case of lesions.

Adult↗

PubMed1979

Free amino acids in motor cortex of amyotrophic lateral sclerosis.

Free amino acids were estimated quantitatively in the motor cortex from 3 patients with amyotrophic lateral sclerosis (ALS) and 11 control subjects. Among 7 amino acids which showed statistically significant changes, taurine was the only one which was increased constantly and most markedly in the motor cortex of all the 3 ALS cases. It was suggested that the metabolism of sulfur amino acids might be affected in comparatively early stages of ALS.

Adult↗

PubMedDate not supplied

Trans-synaptically induced bursts in regular spiking non-pyramidal cells in deep layers of the cat motor cortex.

In deep layers of the cat motor cortex, we have investigated the properties of neurons displaying trans-synaptically induced bursts. In in vivo experiments, extracellularly recorded burst neurons were separated into two subtypes based on their dependence on stimulation sites, the medullary pyramid or the ventrolateral (VL) thalamic nucleus, from which bursts of 10-20 spikes were triggered. The spike amplitude attenuation and frequency adaptation during a burst were more prominent in pyramid-dependent burst neurons than in VL-dependent burst neurons. Intracellular recordings in in vivo experiments revealed that pyramid-dependent bursts emerged from a long-lasting depolarization, while each spike during a VL-dependent burst was narrow in half-width and was followed by a fast AHP, similar to fast spiking neurons. In in vitro slice experiments, intracellular recordings were obtained from neurons that displayed a burst of attenuated spikes emerging from a long-lasting depolarization, and were also obtained from fast spiking neurons. They were morphologically recovered to be multipolar cells with sparsely spiny dendrites and local axonal networks, suggesting that they are inhibitory interneurons. The multipolar neurons displaying bursts of attenuated spikes may mediate the recurrent inhibition of pyramidal tract cells.

Adaptation, Physiological↗

PubMed2000

Subthreshold prefrontal repetitive transcranial magnetic stimulation reduces motor cortex excitability.

The prefrontal cortex plays an important role in central motor control. We have examined whether prefrontal repetitive transcranial magnetic stimulation (rTMS) induces changes of motor cortex excitability determined by motor evoked potentials (MEPs) following single-pulse TMS. We studied 18 healthy volunteers stimulated at 5 Hz with 10% subthreshold prefrontal vs. occipital rTMS for 12 s. MEPs from the flexor carpi radialis muscle after single-pulse vertex stimulation were recorded during rTMS at 0, 4, 8, and 12 s. MEP areas decreased significantly after 8 s of prefrontal rTMS (P < 0. 05) but not after occipital rTMS. We conclude that rTMS of the prefrontal cortex may inhibit the primary motor areas.

Adult↗

PubMed2005

Comparing information about arm movement direction in single channels of local and epicortical field potentials from monkey and human motor cortex.

Cortical field potentials have been used for decades in neurophysiological studies to probe spatio-temporal activity patterns of local populations of neurons. Recently, however, interest in these signals was spurred as they were proposed as potential control signals for neuronal motor prostheses, i.e., for devices fit to record and decode brain activity to restore motor functions in paralyzed patients. Little is known, however, about the functional significance of these cortical field potentials. Here we compared information about arm movement direction in two types of movement related cortical field potentials, obtained during a four direction center-out arm reaching paradigm: local field potentials (LFPs) recorded with intracortical micro-electrodes from monkey motor cortex, and epicortical field potentials (EFPs) recorded with macro-electrode arrays subdurally implanted on the surface of the human cerebral cortex. While monkey LFPs showed a typical sequence of positive and negative potential peaks, an initial negative peak was the most salient feature of human EFPs. Individual contralateral LFPs from the monkey motor cortex carried approximately twice as much decoded information (DI) about arm movement direction (median 0.27 bit) as did individual EFPs from the contralateral hand/arm area of primary motor cortex in humans (median 0.12 bit). This relation was similar to the relation between median peak signal-to-noise ratios for directional modulation of movement related potentials (MRPs) of both types of signals. We discuss possible reasons for the observed differences, amongst them epi- vs. intracortical recording and the different electrode dimensions used to measure EFPs and LFPs.

Action Potentials↗

PubMed1994

Interhemispheric structural asymmetry induced by a lateralized reaching task in the rat motor cortex.

The effects of a lateralized reaching task on the morphological structure of the rat motor cortex were studied during the early postweaning period. Our results show that the consistent use of one forelimb accounts for a significant decrease in the numerical density of cells and an increase in cortical thickness of the contralateral 'forelimb' motor cortex. As a consequence of the early motor training the cell distribution, which is lower rostrally than caudally in nontrained hemispheres, is reversed in the trained hemispheres. This may be interpreted as the specific motor training triggering a higher neuronal branching in the corresponding cortical region. The present findings may further the understanding of the mechanisms involved in the generation of morphological brain asymmetries.

Animals↗

PubMed1987

[Effect of the cerebrospinal fluid from animals with motor cortex damage on the compensation of movement disorders].

Recipient rats with unilateral ablation of the motor cortex underwent suboccipital injection of the CSF obtained from donor rats with analogous damages of their motor cortex. The dose 150 microliter of the donor CSF was most effective rendering a considerable improvement of motor functions in the recipient rats. The data obtained suggest an essentially new technique of human brain trauma therapy using injections of donor CSF.

Adaptation, Physiological↗

PubMed2005

The neurophysiology of response competition: motor cortex activation and inhibition following subliminal response priming.

Some widely used tasks in cognitive neuroscience depend on the induction of a response conflict between choice alternatives, involving partial activation of the incorrect response before the correct response is emitted. Although such ''conflict tasks'' are often used to investigate frontal-lobe-based conflict-monitoring processes, it is not known how response competition evolves in the motor cortex. To investigate the dynamics of motor cortex activation during response competition, we used a subliminal priming task that induced response competition while bypassing pre-response stage processing conflict. Analyses of movement-related EEG potentials supported an interaction between competing responses characterized by reciprocal inhibition. Inhibitory interactions between response channels contribute to the resolution of response conflict. However, the reciprocal inhibition at motor cortex level seemed to operate independent of higher level conflict-monitoring processes, which were relatively insensitive to response conflict induced by subliminal priming. These results elucidate how response conflict causes interference as well as the conditions under which frontal-lobe-based interference control processes are engaged.

Adult↗