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PubMed1995

[The structure of the motor cortex in the rat in hypokinesia].

Ultrastructure of neurons, synapses and glial elements was studied in the rat motor cortex under exposure to hypokinesia lasting for 40 and 90 days. Changes prevail in all cortical layers in 90-days hypokinesia and in upper ones in 40-days hypokinesia. These are basically reactive or not deep destructive changes. Cell elements and synapses with structural manifestations of low functional activity prevail with the increase of the experimental terms. Astrocyte number including satellite forms significantly grows in 40-days hypokinesia. In 90-days changes occur in all cortical layers with the increase of both astrocyte and oligodendrocyte number.

Animals↗

PubMed2001

Dissociation of supplementary motor area and primary motor cortex in human subjects when comparing index and little finger movements with functional magnetic resonance imaging.

This study provides the first investigation of supplementary motor area (SMA) and primary motor cortex (MI) activation with similar movements differing only in subjective difficulty of motor control. Brain activation with simple tapping of the right index finger (well trained during daily life and easy to perform) was compared with tapping of the little finger (less trained and difficult to perform) using functional magnetic resonance imaging at 3 Tesla. Due to optimised movement standardisation, extrinsic influences on activation levels such as movement complexity, amplitude and frequency were minimised. Fifth finger tapping significantly increased the number of activated SMA voxels by 450% whereas MI activation showed no significant difference between fingers. We conclude that with similar movements the degree of subjective difficulty specifically modifies SMA but not MI activation.

Adult↗

PubMed1991

Long-term potentiation of thalamic input to the motor cortex induced by coactivation of thalamocortical and corticocortical afferents.

1. Intracellular recordings were obtained from neurons in the motor cortex (MCx), in which excitatory postsynaptic potentials (EPSPs) were evoked by microstimulation of the somatosensory cortex (SCx) and the ventrolateral nucleus (VL) of the thalamus. The effects of combined tetanic stimulation of SCx and VL on the amplitudes of these EPSPs were studied. 2. Amplitudes of both corticocortical (CC) and thalamocortical (TC) EPSPs were potentiated after combined tetanic stimulation. This potentiation occurred exclusively in neurons that were located in the superficial layers (II/III) and that received direct input from both the SCx and VL, with both inputs synapsing in close proximity to each other. In all cases, the potentiation lasted until the electrode went out of the cell (21 +/- 25 min, mean +/- SD) the longest being 90 min. We therefore refer to this potentiation as long-term potentiation (LTP). 3. Tetanic stimulation of the thalamus only did not produce LTP in neurons receiving direct input from the VL. 4. LTP was not induced in either CC or TC EPSPs in neurons located in layer V and/or in neurons receiving long-latency CC EPSPs. 5. It is concluded that TC input from the VL to the MCx is potentiated only when coactivated with the CC input from the SCx.

Animals↗

PubMed1996

Long-term depression of horizontal connections in rat motor cortex.

The possibility for long-term depression (LTD) of synaptic transmission in layer II/III horizontal connections within motor cortex was investigated using field potentials and intracellular recordings in rat brain slices. The LTD was induced by low-frequency stimulation at 2 Hz for 10 min in sites displaced horizontally by 0.5 mm from the stimulating electrode. Response amplitude measured 25-30 min after 2 Hz stimulation ended was 79% of baseline values (n = 13) at half maximal stimulation and 59% when 2 Hz stimulus intensity was doubled (n = 10). In 13/15 tested cases LTD in horizontal connections was specific to the activated pathway. Intracellular recordings from six neurons confirmed synaptic character of response depression. Horizontal connections in which LTD was induced retained the capability of increasing synaptic strength. Long-term potentiation could be induced in previously depressed pathways by simultaneous theta burst stimulation of two converging horizontal inputs combined with transient local application of GABA(A) receptor antagonist bicuculline methiodide (mean increase: 45 +/- 8% n = 6) or by simultaneous theta burst stimulation of converging horizontal and vertical inputs (mean change: 26 +/- 6%, n = 5). These data demonstrate that activity-dependent mechanisms may regulate bidirectionally the effectiveness of horizontal synaptic coupling between cortical neurons, thus forming a potential mechanism for plasticity of cortical connections and the representation patterns they support.

Action Potentials↗

PubMed2005

Motor cortex excitability following repetitive electrical stimulation of the common peroneal nerve depends on the voluntary drive.

Previously, long-term changes in the motor cortex have been reported after repetitive electrical nerve stimulation (rES) as well as after motor exercise. The purpose of this study was to investigate whether the effects of voluntary motor cortical drive and of rES on the motor cortical output in healthy subjects interact with each other. A 30-min exercise session was performed during the following conditions: rES of the right common peroneal nerve (CPN) during rES at rest (A); voluntary exercise of the right ankle dorsiflexors alone (B); rES combined with voluntary dorsiflexion exercise (C); voluntary exercise of ankle plantar flexors alone (D); and plantar flexion exercise combined with rES (E). Motor evoked potentials (MEPs) were obtained before and after the exercise with a stimulation intensity of 125% of the threshold of the relaxed right tibialis anterior (TA). rES was ON for 1 s and OFF for 2 s in a cycle, and consisted of trains of five pulses, duration 1 ms and frequency 30 Hz, as applied in functional electrical stimulation (FES). MEPs of the TA muscle elicited after the training were increased in A by 38%, in B by 35%, and in C by 66%. In D and E, the MEPs of TA were decreased by 29% and 35%, respectively. The effect was maintained for at least 30 min after the nerve stimulation was completed. Consistent with previous studies (Khaslavskaia et al. (2002) Exp Brain Res 145:309-315), MEPs after the CPN rES are shown to be partly due to increased TA cortical excitability. These results suggest that the effect of FES on motor cortical excitability depends on the concurrent motor cortical drive present at the time of FES, and the combination of these factors modulates neural excitability and probably reorganization. The decrease in motor cortical excitability after plantar flexor exercise probably means that voluntary effort antagonistic to the electrical exercise is stronger and cancels out the effects of rES. Improving FES effects through an agonist voluntary drive implies an enhancement of sensorimotor reorganization through the addition of a voluntary component to a trained movement. Possible mechanisms and implications of these results on the rehabilitation of patients with paralysis and spasticity are discussed.

Adaptation, Physiological↗

PubMed2006

Chronic inhibition of cyclooxygenase-2 induces dendritic hypertrophy and limited functional improvement following motor cortex stroke.

The cyclooxygenase-2 (COX-2) enzyme is part of the inflammatory pathway and is induced within the brain by a variety of pathological events, including ischemia. Pharmacological agents that inhibit COX-2 have been found to be neuroprotective in a number of injury models, and long-term administration of these drugs has been shown to induce plastic changes in the brain. In the current experiment, we investigated the effectiveness of stimulating cortical plasticity following stroke injury through the administration of the COX-2 inhibitor drug NS398. Furthermore, we determined whether the induced plastic changes improved functional outcome following motor cortex stroke. Chronic drug administration was found to induce dendritic hypertrophy in cells in the parietal cortex, and this anatomical change was associated with the animals making significantly more reach attempts, as well as successful reaches during a skilled reaching task. Additional motor tests however revealed that the treatment did not affect the level of motor recovery, as the animals showed chronic impairments in the Schallert cylinder, and the forepaw inhibition tasks. Short-term administration of the drug, immediately following the stroke did not induce any dendritic changes, nor was it found to improve behavioral performance on any of the motor tasks. Based on these results we conclude that the plastic changes that are induced by long-term COX-2 inhibitor administration provide some benefit to functional outcome following ischemic cortical injury.

Animals↗

PubMed1997

Bilateral coupling in learned blinking: effects of lesion aimed at callosal disconnection of the cat motor cortex.

The effects of selective transection of the rostralmost portion of the corpus callosum, which contains fibers interconnecting the motor cortices of the two hemispheres, on interocular temporal coupling in the initiation of learned symmetrical blinking were examined in 5 cats trained to blink in response to a 500-ms tone paired with 100-ms airpuffs randomly delivered to either eye (alternate airpuff; 3 animals) or simultaneously directed to both eyes (bilateral airpuff; 2 animals) 400 ms after tone onset. Lesioning had no effect on ability to respond, but did cause a significant increase in the mean conditioned response (CR) latencies of both eyes in all subjects. In the intact cats, a statistically significant difference between the mean CR latencies of the two eyes (hereafter called side superiority) was found in three animals, two of which exhibited superiority of the left eye. After lesioning, it was found that the right eye proved superior to the left eye in four subjects. Both before and after lesioning, side superiority was not due to the ability of one eye to give CRs consistently shorter than those of the other eye, but it crucially depended on the higher proportion of trials in which the superior eye led. A linear correlation between CR latencies of the right and left eye was found in all animals both before and after lesioning. It is suggested that subsequent to lesioning aimed at callosal disconnection of the motor cortex, the effects on initiation of learned symmetrical blinking are the consequences of withdrawal of both bilaterally balanced modulatory influences to both eyes and lateralized modulatory influences to the left eye.

Animals↗

PubMed1976

[Effect of ablation of the motor cortex or the cerebellum on postural-kinetic coordination in the cat].

1. A cat, restrained in a hammock, stands with its feet on supporting trays each furnished with strain gauges to measure the isometric upthrust. Placing reactions are elicited by contact of the left or right forelimb with a moving tray. The placing movement is preceded and accompanied by a postural adjustment characterized by an increase of the upthrust exerted by the opposite forelimb. 2. After ablation of the motor cortex on one side, the placing movement of the contralateral forelimb is abolished for the first few days after the operation and thereafter is delayed. However, the postural adjustment of the ipsilateral forelimb persists, with the same range of latencies as before the operation. 3. After unilateral motor cortical ablation, the contralateral forelimb still takes part in the postural adjustment associated with the placing movement of the other forelimb. 4. In two cats which had 2 years earlier undergone a total cerebellectomy, the placing movement was lacking or appeared with a long delay, whereas a postural adjustment of the other forelimb could be observed, although reduced. 5. The results indicate that the nervous structures responsible for the movement and for the associated postural adjustment are separate but partially linked.

Animals↗

PubMed1985

Cross correlation studies in primate motor cortex: event related correlation.

Simultaneous extracellular unit recordings were made from each cell of 237 pairs in two awake monkeys, during a voluntary reaching movement of the forelimb. The cells were located in contralateral precentral cortex and functionally coupled to single forelimb joints, as indicated by intracortical microstimulation and passive sensory stimulation. Cross correlation analysis showed that 72 of these pairs exhibited significant event-related correlation over periods of up to 780 ms, comparable to and coincident with the forelimb movement. Spatial analysis showed that such correlation extended across contiguous portions of all four forelimb joint zones of precentral cortex, over distances up to 3.5 mm. No preferred direction of correlation was observed. The data confirm the previously described nested organization of the forelimb area of precentral cortex. Findings are discussed in terms of mechanisms by which columns of neurons in motor cortex participate in the reaching movement.

Animals↗

PubMed2001

Motor cortex excitability following short trains of repetitive magnetic stimuli.

Trains of repetitive transcranial magnetic stimuli (rTMS) appear to have effects on corticospinal excitability that outlast the duration of the train. In order to investigate the mechanism of this effect in more detail we applied short periods of rTMS consisting of up to 20 stimuli at 5 Hz, 10 Hz or 20 Hz (rTMS) to the motor cortex at an intensity equal to resting threshold in 11 healthy, relaxed subjects. Spinal excitability, as judged by effects on the H-reflex or on transcranial anodal facilitation of the H-reflex, was not affected by the rTMS. However, cortical excitability, as judged by the effect on the size of EMG responses evoked by a suprathreshold TMS pulse, was decreased for up to 1 s after the end of rTMS. Post-train suppression was more powerful following longer trains or higher frequencies of rTMS. The predominant suppression contrasts with previous reports of facilitation, particularly after high-frequency rTMS. A second set of experiments, however, showed that this could be converted into facilitation if the intensity of rTMS was increased. We conclude that the after-effects of rTMS depend on its frequency, intensity and duration. The results are consistent with a model in which inhibition and facilitation build up gradually during the course of a conditioning train. Inhibition reaches its maximum effect after only a small number of stimuli, whereas facilitation takes longer. The threshold for evoking inhibition is lower than that for facilitation. Thus if moderate intensities of conditioning train are applied, inhibition is predominant after short trains, whereas facilitation dominates after long trains.

Adult↗

PubMed1997

Sequential activation of supplementary motor area and primary motor cortex during self-paced finger movement in human evaluated by functional MRI.

The 'Bereitschaftspotential' attributed to activation of the supplementary motor area (SMA) precedes the 'motor potential' of the primary motor cortex (Ml) about 500-1000 ms during self-initiated movements. A measurement procedure is reported to evaluate the sequence of hemodynamic activation within both motor areas by functional magnetic resonance imaging (fMRI). The fMRI-data were averaged across multiple trials of single voluntary finger movements and analyzed with respect to the onset-time of signal increase. All participants showed a sequential hemodynamic response with SMA preceding M1 activation. The mean latency between hemodynamic activation of SMA and M1 amounted to 0.8 s. These findings suggest that the vascular response parallels the electrical events and that a sufficient temporal resolution can be achieved by fMRI to detect sequential hemodynamic activation of functionally connected cortical areas.

Adult↗

PubMed1997

Functional properties of neurons in the primate tongue primary motor cortex during swallowing.

Recent studies conducted in our laboratory have suggested that the tongue primary motor cortex (i.e., tongue-MI) plays a critical role in the control of voluntary tongue movements in the primate. However, the possible involvement of tongue-MI in semiautomatic tongue movements, such as those in swallowing, remains unknown. Therefore the present study was undertaken in attempts to address whether tongue-MI plays a role in the semiautomatic tongue movements produced during swallowing. Extracellular single neuron recordings were obtained from tongue-MI, defined by intracortical microstimulation (ICMS), in two awake monkeys as they performed three types of swallowing (swallowing of a juice reward after successful tongue task performance, nontask-related swallowing of a liquid bolus, and nontask-related swallowing of a solid bolus) as well as a trained tongue-protrusion task. Electromyographic activity was recorded simultaneously from various orofacial and laryngeal muscles. In addition, the afferent input to each tongue-MI neuron and ICMS-evoked motor output characteristics at each neuronal recording site were determined. Neurons were considered to show swallow and/or tongue-protrusion task-related activity if a statistically significant difference in firing rate was seen in association with these behaviors compared with that observed during a control pretrial period. Of a total of 80 neurons recorded along 40 microelectrode penetrations in the ICMS-defined tongue-MI, 69% showed significant alterations of activity in relation to the swallowing of a juice reward, whereas 66% exhibited significant modulations of firing in association with performance of the trained tongue-protrusion task. Moreover, 48% showed significant alterations of firing in relation to both swallowing and the tongue-protrusion task. These findings suggest that the region of cortex involved in swallowing includes MI and that tongue-MI may play a role in the regulation of semiautomatic tongue movement, in addition to trained motor behavior. Swallow-related tongue-MI neurons exhibited a variety of swallow-related activity patterns and were distributed throughout the ICMS-defined tongue-MI at sites where ICMS evoked a variety of types of tongue movements. These findings are consistent with the view that multiple efferent zones for the production of tongue movements are activated in swallowing. Many swallow-related tongue-MI neurons had an orofacial mechanoreceptive field, particularly on the tongue dorsum, supporting the view that afferent inputs may be involved in the regulation of the swallowing synergy.

Animals↗

PubMed1978

Intracortical horizontal connections of neurons in cat and monkey motor cortex.

The present paper deals with the study of the structure of horizontal neuron chains, one of the aspects of intracortical intraneuronal relationships. The motor cortex (field 4) of cats and lower monkeys (Papio hamadryas and Macacus rhesus s. M. mullata) was treated by the impregnating method of Golgi--Kopsh. The drawings of neurons from 90-micrometer sections were made by means of a camera lucida. Three possible pathways of impulse transmission along neuron chains in a horizontal direction were revealed. These were: a pyramido-pyramidal system of connections which may possibly spread excitatory influence among several columns; a basket-pyramidal connection system; and connections which arise from successive switchings between neighboring neurons of one layer.

Animals↗

PubMed1988

Do neurons in the motor cortex encode movement direction? An alternative hypothesis.

Previous investigations by Georgopoulos et al. of cell activities in the primate motor cortex during the execution of voluntary arm movements have shown that these cells are characterized by tuning properties related to the direction of hand trajectories. Here, it is demonstrated that these findings do not necessarily imply that cortical cells encode spatial features of hand movements and an alternative hypothesis is considered according to which cortical cells encode muscle state variables. It is shown that this hypothesis would lead both to the single-cell activities and to the population behaviors observed by Georgopoulos et al.

Animals↗

PubMed2006

Correlations between the same motor cortex cells and arm muscles during a trained task, free behavior, and natural sleep in the macaque monkey.

Traditionally, the neural control of movement has been studied by recording cell activity in restrained animals performing repetitive, highly trained tasks within a restricted workspace. However, the degree to which results obtained under these conditions are valid during natural, unconstrained behavior remains unknown. Using an autonomous, implantable recording system, we examined the relationships between the firing of motor cortex cells and forearm muscle activity in primates under three behavioral conditions: performance of a conventional torque-tracking task, unrestrained behavior, and natural sleep. We found strong correlations over long periods of daytime activity, suggesting a consistent relationship between cortex and muscles across the repertoire of awake behavior. The range of correlation values was comparable during task performance, but many individual cells exhibited significant differences across conditions. During the night, phases of sleep were associated with a cyclical pattern of cell and muscle activity. Across the population, the strength of cell-muscle correlations was related to preferred direction for daytime but not nighttime activity. The relationship of cells to behavior remained consistent over periods of several weeks. These findings extend the interpretation of results obtained under constrained conditions and are relevant to the development of neural prostheses for restoring natural movements to patients with motor deficits.

Action Potentials↗

PubMed2006

Half sine, monophasic and biphasic transcranial magnetic stimulation of the human motor cortex.

OBJECTIVE: To compare half sine transcranial magnetic stimuli (TMS) with conventional monophasic and biphasic stimuli, measuring resting and active motor threshold, motor evoked potential (MEP) input/output curve, MEP latency, and silent period duration. METHODS: We stimulated the dominant hand representation of the motor cortex in 12 healthy subjects utilising two different MagPro stimulators to generate TMS pulses of distinct monophasic, half sine and biphasic shape with anteriorly or posteriorly directed current flow. RESULTS: The markedly asymmetric monophasic pulse with a posterior current flow in the brain yielded a higher motor threshold, a less steep MEP input/output curve and a longer latency than all other TMS types. Similar but less pronounced results were obtained with a less asymmetric half sine pulses. The biphasic stimuli yielded the lowest motor threshold and a short latency, particularly with the posterior current direction. CONCLUSIONS: The more asymmetric the monophasic pulse, the stronger the difference to biphasic pulses. The 3rd and 4th quarter cycle of the biphasic waveform make it longer than any other waveform studied here and likely contribute to lowering motor threshold, shortening MEP latency and reversing the influence of current direction. SIGNIFICANCE: This systematic comparison of 3 waveforms and two current directions allows a better understanding of the mechanisms of TMS.

Adult↗

PubMed2000

Changes in motor cortex excitability during ipsilateral hand muscle activation in humans.

OBJECTIVES: To test whether unilateral hand muscle activation involves changes in ipsilateral primary motor cortex (M1) excitability. METHODS: Single- and paired-pulse transcranial magnetic stimulation (TMS) of the right hemisphere was used to evoke motor evoked potentials (MEPs) from the resting left abductor pollicis brevis (APB) in 9 normal volunteers. We monitored changes in motor threshold (MT), MEP recruitment, intracortical inhibition (ICI) and intracortical facilitation (ICF) while the ipsilateral right APB was either at rest or voluntarily activated. Spinal motoneuron excitability was assessed using F-wave recording procedures. RESULTS: Voluntary muscle activation of the ipsilateral APB significantly facilitated the MEPs and F-waves recorded from the contralateral APB. Facilitation was observed with muscle activation >50% of the maximum voluntary force and with stimulus intensities >20% above the individual resting motor threshold. Intracortical inhibition significantly decreased in the ipsilateral M , while there was no significant change in intracortical facilitation during this maneuver. CONCLUSIONS: Unilateral hand muscle activation changes the excitability of homotopic hand muscle representations in both the ipsilateral M1 and the contralateral spinal cord. While the large proportion of MEP facilitation most likely occurred at a spinal level, involvement of the ipsilateral hemisphere may have contributed to the enlargement of magnetic responses.

Adult↗

PubMedDate not supplied

[The assessment of the strength of the interaction between neurons of the cat motor cortex in a conditioned reflex to time].

The work was conducted on cats with recording multineuronal activity of the motor cortex at the elaboration of conditioned reflex to time. Strength of interaction was estimated between the adjacent and remote neurones in the limits of 0.5 m. The dynamics of strengths of interneuronal interaction in most cases did not correlate with the dynamics of impulses frequency of the studied neurones. Changes of strengths of interaction between mutually remote neurones at CRT were met more frequently than between the adjacent ones, what may serve as one more evidence of the hypothesis on more strict structure of connections within microsystems and greater plasticity of connections between microsystems.

Action Potentials↗