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PubMed1994

[Influence of cooling motor cortex on the inhibitory effect of stimulation of SII on nociceptive responses in ILN neurons].

Fibers from the cortical somatosensory area II (SII) or motor cortex (MCtx) to intralaminar nuclei (ILN) have been proven to exist, and SII was found to be connected with MCtx by cortico-cortical fibers. The present work was undertaken to study whether MCtx participated in SII producing descending modulation of ILN. All experiments were performed on sodium pentobarbitone anaesthetised cats. Single unit activities of ILN neurons were extracellularly recorded by glass microelectrodes. The effects of stimulating SII on nociceptive responses of ILN neurons were observed before and after cooling MCtx. The nociceptive responses of ILN neurons were attenuated by stimulating SII. There was a statistically significant difference at 0'-2' after the stimulation (n = 14, P < 0.05). The inhibitory effect of stimulating SII was reduced after cooling MCtx (19 degrees C-20 degrees C) in 8 neurons, and abolished in other neurons when the temperature was below 18 degrees C. MCtx was involved in SII producing descending modulation of ILN.

Animals↗
PubMedDate not supplied

Long-term ongoing reorganizations of the processes of analysis of kinesthetic afferentation at the level of cat motor cortex neurons after damage to the ventrolateral nucleus of the thalamus.

The changes in the functional characteristics of neurons of field 4 of the motor cortex (MC) of cats before and at various times (from a week up to five months) following an ipsilateral lesion of the ventrolateral nucleus of the thalamus were investigated in semichronic experiments. The reactions of the cells to tactile stimulation of the forelimb and its passive movement at the wrist at an average speed of 170 degrees/sec were studied. It was demonstrated that a correlation between the impulse activity at speed maxima and the acceleration of monoarticular movement is characteristic for a number of cells of the MC of the intact brain. Experimental confirmation was obtained of the hypothesis, formulated on the basis of the results of preceding investigations, regarding a disturbance of the mechanism of detection by MC neurons of the kinematic indicators of movement following damage to the thalamus. It was established that compensation of this disturbance is associated with the facilitation of conduction to MC neurons of somatosensory afferentation. It is concluded that a morphofunctional reorganization of particular intracortical components of sensorimotor coupling underlies the mechanisms of the compensatory plasticity of the MC.

Acceleration↗
PubMed1992

[Effect of cat motor cortex on the formation of lateral geniculate nucleus responses evoked by contralateral superior colliculus stimulation].

It was shown in experiments on anesthetized cats that motor cortex (MC) stimulated by single current pulse caused formation of the lateral geniculate nucleus (LGN) response. It was established that changes in formation of LGN response evoked by contralateral superior colliculus (SC) stimulation were observed by condition of the precedence of LGN response evoked by stimulation of the MC. The expressiveness level of that decrease depended on intervals between conditioning cortical and testing tectal stimuli. At the same time the stimulation of the MC by single current pulse caused no changes in formation of the visual evoked potential of LGN. However, a significant decrease of the visual response of that part of the SC which stimulation caused formation of the LGN response was observed under the same conditions. The obtained data permit supposing that MC checks realization of the tectal influences on the LGN function on the tectal level. It is assumed that realization of the effect of the saccadic suppression of the LGN function in which accomplishment, as it was supposed earlier, the SC took part, was controlled by the MC phasic influence.

Animals↗
PubMedDate not supplied

[Vibrissal inputs into the motor cortex of adult and developing rats].

Field potentials (FP) and responses of single neurones to electrical stimulation of vibrissal pads have been recorded in motor cortex in the albino mature and developing rats. The FPs were characterized by 3-phasic shape and high stability in mature rats. The FPs evoked by contralateral stimuli have a range of onset latency of 4 to 24 ms (peak of distribution 8-11 ms); those to ipsilateral stimuli have a latency of 4 to 23 ms (peak of distribution 12-16 ms). Responses of single neurones were evoked with a latency of 9 to 20 ms. Usually, the FPs were evoked by both contralateral and ipsilateral stimulation, and in some tracks were effective only ipsilateral stimuli in the developing rats beginning from the 11th day of life. The FPs in such animals were less stable and more fatigable. During 2-4 weeks of life, FPs evoked by contralateral stimulation appeared with a latency of 15 to 46 ms; during the same period, a latency of single unit responses ranged between 20 to 33 ms. The FPs to ipsilateral stimuli appeared with a latency of 18 to 47 ms, a latency of single unit responses of 27 to 47 ms. The results indicate functional immaturity of vibrissal system up to the end of the first month of rat life.

Afferent Pathways↗
PubMed2005

Motor evoked potentials following highly frequent transcranial magnetoelectrical motor cortex stimulation: normal data and potential modulation by stimulation-dependent inhibitory and activating mechanisms.

OBJECTIVE: To determine the normal values (latency, amplitude) of motor evoked potentials (MEP) of the abductor pollicis brevis (APB) and tibialis anterior (TA) muscle after high-frequency repetitive transcranial magnetic stimulation of the motor cortex (rTCMS), and to evaluate stimulation-dependent MEP modulations. PATIENTS AND METHODS: 29 healthy volunteers underwent rTCMS with 2 and 4 stimuli. The interstimulus interval (ISI) was 2, 3, and 4 ms respectively, which corresponded to frequencies between 250 and 500 stimuli/s. The evoked potentials of the relaxed and voluntarily contracted APB and TA were registered. RESULTS: Depending on the frequency and number of stimuli, the mean corticomuscular latency to the relaxed APB varied between 22.2 and 22.9 ms, and to the relaxed TA between 30.4 and 32.0 ms. The intra- and interindividual variability of the amplitudes was substantial. Voluntary contraction of the target muscle always led to a decrease in latency and increase in amplitude (p < 0.05). CONCLUSION: The high variability of the amplitudes does not allow the computation of meaningful normal values. The latencies after rTCMS are close to those of normal data after single TCMS, which indicates that in awake humans identical cortical and spinal structures are similarly activated. The discrete variations of latency and amplitude after changing the frequency and stimulus number suggest that inhibitory and excitatory mechanisms on the cortical and/or spinal level modulate the muscle response.

Adult↗
PubMed1991

Effects of torque disturbances on elbow joint movements evoked in unanesthetized cats by microstimulation of the motor cortex.

Flexion and extension movements were evoked in the elbow joint of unanesthetized cats by intracortical microstimulation (ICMS) applied to deep layers of the motor cortex (areas 4 and 6). Pulse trains with duration up to 3-4 s, current intensities of 15-50 microA and rates of approximately 100/s were used. Cortically evoked movements (CEMs) were tested mechanically by applying servo-controlled torque disturbances to the joint. The disturbances consisted of two reciprocating sinusoidal pulses of torque with fixed frequencies (1.2 or 3.2 Hz). A pronounced torque-angle hysteresis with long-lasting after-effects was revealed in the presence of the torque disturbances that opposed the CEMs and/or assisted them. Two parameters were introduced to describe the mechanical testing of the CEMs quantitatively: (1) the resulting stiffness (RS) defined during the forward and reverse phases of the disturbed movement as a ratio between the amplitudes of torque wave and the overall change of angle at these phases; (2) uncertainty index (UI) defined as the subtraction of forward and reverse angle changes, which was normalized by the first of these two values. RS was shown to be dependent on the immediate past movement history of the joint, it increased with changes in the direction of movement, and its magnitude during such changes could be several times higher than when the disturbance was in the same direction as the movement.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

A comparison of corticospinal activation by magnetic coil and electrical stimulation of monkey motor cortex.

The effects of different orientations of a Cadwell round magnetic coil (MC) were compared with each other and with surface electrical stimulation of motor cortex in monkeys anesthetized with pentobarbital or urethane. Recordings were made from within the lateral corticospinal tract, either from axonal populations or with a microelectrode from individual axons. A lateral-sagittally orientated MC directly excited corticospinal neurons at lower stimulus intensity than was required for indirect, i.e., transsynaptic excitation via inputs to corticospinal neurons. By contrast, in 2 out of 3 macaques tested, a vertex-tangential orientation could excite corticospinal neurons indirectly at lower intensities than were required for direct excitation; at higher intensities, direct excitation also occurred. The site of direct corticospinal excitation by a lateral-sagittally orientated MC was inferred by comparing the response variability and latency to MC and surface electrical stimuli. Cathodal stimuli elicited more variable corticospinal population responses and later individual axonal responses than were obtained with anodal stimuli. The variability in response is attributed to interaction between nearby, on-going synaptic bombardment and the stimulus, implying that surface cathodal stimuli directly activate corticospinal neurons at the spike trigger zone (presumably the initial segment). By contrast, the consistency and reduced latency of the corticospinal responses to surface anodal stimuli are attributed to the direct excitation of corticospinal fibers within the white matter. When the stimulus intensity is clearly above threshold, surface anodal and cathodal stimuli can activate corticospinal neurons both directly and indirectly. Direct corticospinal excitation by the MC can resemble the effects of either surface anodal or surface cathodal stimuli. We conclude that the MC can activate corticospinal neurons at the spike trigger zone or their fibers deeper in white matter. The findings in the monkey are used to interpret the effects of different MC orientations in the human.

Action Potentials↗
PubMed2003

Motor cortex hand area and speech: implications for the development of language.

Recently a growing body of evidence has suggested that a functional link exists between the hand motor area of the language dominant hemisphere and the regions subserving language processing. We examined the excitability of the hand motor area and the leg motor area during reading aloud and during non-verbal oral movements using transcranial magnetic stimulation (TMS). During reading aloud, but not before or afterwards, excitability was increased in the hand motor area of the dominant hemisphere. This reading effect was found to be independent of the duration of speech. No such effect could be found in the contralateral hemisphere. The excitability of the leg area of the motor cortex remained unchanged during reading aloud. The excitability during non-verbal oral movements was slightly increased in both hemispheres. Our results are consistent with previous findings and may indicate a specific functional connection between the hand motor area and the cortical language network.

Adult↗
PubMed1986

Functional metabolic mapping during forelimb movement in rat. I. Stimulation of motor cortex.

The quantitative 14C-deoxyglucose (DG) autoradiographic technique has been used to study changes in cerebral metabolism during forelimb movements induced by graded stimulation of motor cortex. Experiments were directed at studying basic physiologic and anatomic aspects of the metabolic changes. Single shocks caused movement without metabolic change, whereas low-frequency trains caused seizures. Repetitive high-frequency train stimuli of short duration (500 Hz for 20 msec) caused jerk movements coupled with DG uptake in pathways. With stimulation of the forelimb motor zone at frequencies of 15-30/min there was prominent activation of cortical columns and strips in ipsilateral SI, SII, and MII, and contralateral MI and SI. Higher frequencies (120/min) were required to cause significant changes in DG in subcortical circuits. The most prominent changes occurred within a longitudinal corridor in dorsal thalamus and a ventral corridor in second-order sites in basal ganglia. Metabolic activation also occurred in contralateral cerebellum, the cuneate nucleus, and dorsal horn of the cervical spinal cord. Changes in these latter two sites were largely eliminated by removing feedback sensory activity. Stimulation of the forelimb sensory zone activated different sites in caudatoputamen and thalamus but similar zones in midbrain and cerebellum. The magnitude of the metabolic response in distant sites depended on the frequency of cortical stimulation. Different frequency-response relationships in different sites seemed to reflect the nature of the cortical input as well as differential effects of anesthesia. The pattern of the metabolic response was studied by comparing sites of activation with sites of the anatomic projections from motor and sensory cortical zones. 3H- and 14C-labeled amino acids were used to map the site and relative strength of pathways. Results revealed good correlation between the site of anatomic projection and the site of DG uptake but no consistent relationship between the relative strength of a projection and the magnitude of metabolic change within its field. Changes in glucose utilization with metabolic mapping experiments depend on the nature, strength, and frequency of stimulation; the site and nature of anatomic projection; the effects of anesthesia; and the strength of sensory feedback associated with the induced behavior.

Animals↗
PubMed1998

Primary motor cortex is involved in bimanual coordination.

Many voluntary movements involve coordination between the limbs. However, there have been very few attempts to study the neuronal mechanisms that mediate this coordination. Here we have studied the activity of cortical neurons while monkeys performed tasks that required coordination between the two arms. We found that most neurons in the primary motor cortex (MI) show activity specific to bimanual movements (bimanual-related activity), which is strikingly different from the activity of the same neurons during unimanual movements. Moreover, units in the supplementary motor area (SMA; the area of cortex most often associated with bimanual coordination) showed no more bimanual-related activity than units in MI. Our results challenge the classic view that MI controls the contralateral (opposite) side of the body and that SMA is responsible for the coordination of the arms. Rather, our data suggest that both cortical areas share the control of bilateral coordination.

Animals↗
PubMed2004

Organization of rat vibrissa motor cortex and adjacent areas according to cytoarchitectonics, microstimulation, and intracellular stimulation of identified cells.

The relationship between motor maps and cytoarchitectonic subdivisions in rat frontal cortex is not well understood. We use cytoarchitectonic analysis of microstimulation sites and intracellular stimulation of identified cells to develop a cell-based partitioning scheme of rat vibrissa motor cortex and adjacent areas. The results suggest that rat primary motor cortex (M1) is composed of three cytoarchitectonic areas, the agranular medial field (AGm), the agranular lateral field (AG1), and the cingulate area 1 (Cg1), each of which represents movements of different body parts. Vibrissa motor cortex corresponds entirely and for the most part exclusively to AGm. In area AG1 body/head movements can be evoked. In posterior area Cg1 periocular/eye movements and in anterior area Cg1 nose movements can be evoked. In all of these areas stimulation thresholds are very low, and together they form a complete representation of the rat's body surface. A strong myelinization and an expanded layer 5 characterize area AGm. We suggest that both the strong myelinization and the expanded layer 5 of area AGm may represent cytoarchitectonic specializations related to control of high-speed whisking behavior.

Action Potentials↗
PubMed2003

Event-related desynchronization and excitability of the ipsilateral motor cortex during simple self-paced finger movements.

OBJECTIVE: To study the time course of oscillatory EEG activity and corticospinal excitability of the ipsilateral primary motor cortex (iM1) during self-paced phasic extension movements of fingers II-V. METHODS: We designed an experiment in which cortical activation, measured by spectral-power analysis of 28-channel EEG, and cortical excitability, measured by transcranial magnetic stimulation (TMS), were assessed during phasic self-paced extensions of the right fingers II-V in 28 right-handed subjects. TMS was delivered to iM1 0-1500 ms after movement onset. RESULTS: Ipsilateral event-related desynchronization (ERD) during finger movement was paralleled by increased cortical excitability of iM1 from 0-200 ms after movement onset and by increased intracortical facilitation (ICF) without changes in intracortical inhibition (ICI) or peripheral measures (F waves). TMS during periods of post-movement event-related synchronization (ERS) revealed no significant changes in cortical excitability in iM1. CONCLUSIONS: Our findings indicate that motor cortical ERD ipsilateral to the movement is associated with increased corticospinal excitability, while ERS is coupled with its removal. These data are compatible with the concept that iM1 contributes actively to motor control. No evidence for inhibitory modulation of iM1 was detected in association with self-paced phasic finger movements. SIGNIFICANCE: Understanding the physiological role of iM1 in motor control.

Adult↗
PubMed1997

Self-organization of firing activities in monkey's motor cortex: trajectory computation from spike signals.

The population vector method has been developed to combine the simultaneous direction-related activities of a population of motor cortical neurons to predict the trajectory of the arm movement. In this article, we consider a self-organizing model of a neural representation of the arm trajectory based on neuronal discharge rates. As self-organizing feature map (SOFM) is used to select the optimal set of weights in the model to determine the contribution of an individual neuron to an overall movement representation. The correspondence between movement directions and discharge patterns of the motor cortical neurons is established in the output map. The topology-preserving property of the SOFM is used to analyze the recorded data of a behaving monkey. The data used in this analysis were taken while the monkey was tracing spirals and doing center-->out movements. The arm trajectory could be well predicted using such a statistical model based on the motor cortex neuronal firing information. The SOFM method is compared with the population vector method, which extracts information related to trajectory by assuming that each cell has a fixed preferred direction during the task. This implies that these cells are acting along lines labeled only for direction. However, extradirectional information is carried in these cell responses. The SOFM has the capability of extracting not only direction-related information but also other parameters that are consistently represented in the activity of the recorded population of cells.

Algorithms↗
PubMed1990

[The effect of noradrenaline on the neuronal reactions of the motor cortex evoked by conditional stimulation].

In chronic experiments on cats the influence of iontophoretic application of adrenomimetic ephedrin and beta-adrenoblocker obsidan (propranolol) on motor cortex neuron reactions following conditional stimuli was investigated under instrumental placing reaction. It was shown for a majority of neurons that the background impulse activity and reactions following conditional stimulation were suppressed by the influence of ephedrin and on the contrary were increased by obsidan application. It is concluded that there exists a consistent tonic suppressing influence of the noradrenergic system on background and evoked cortical neurons impulse activity in the natural state. It is supposed that noradrenergic influence temporal increase may serve as an important link in mechanisms of external inhibition during stress situations, aversive effects, and distractive external excitations.

Acetylcholine↗
PubMedDate not supplied

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

The study was carried out in cats, with the recording of multineuronal activity of the motor cortex during the development of a conditioned reflex to time. The strength of the interaction between adjacent and remote neurons within a range of 0.5 mm was assessed. The dynamics of the strength of the interneuronal interaction did not correlate in the overwhelming majority of cases with the dynamics of the frequency of the impulse activity of the neurons under investigation. Changes in the strength of interaction between neurons separated from one another in a conditioned reflex (CR) to time were encountered more often than between adjacent neurons; this may serve as additional evidence in favor of the hypothesis of the more rigid structure of connections within microsystems and the greater plasticity of connections between microsystems.

Animals↗
PubMed2000

Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation.

In this paper we demonstrate in the intact human the possibility of a non-invasive modulation of motor cortex excitability by the application of weak direct current through the scalp. Excitability changes of up to 40 %, revealed by transcranial magnetic stimulation, were accomplished and lasted for several minutes after the end of current stimulation. Excitation could be achieved selectively by anodal stimulation, and inhibition by cathodal stimulation. By varying the current intensity and duration, the strength and duration of the after-effects could be controlled. The effects were probably induced by modification of membrane polarisation. Functional alterations related to post-tetanic potentiation, short-term potentiation and processes similar to postexcitatory central inhibition are the likely candidates for the excitability changes after the end of stimulation. Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive, painless, reversible, selective and focal way.

Adult↗
PubMed1996

Biphasic reorganization of somatotopy in the primary motor cortex follows facial nerve lesions in adult rats.

Effects of facial nerve transection were studied on muscle responses evoked by electrical stimulation in the primary motor cortex (MI) of adult rats. In intact animals, activated muscles varied according to the somatotopic representation map, and responses were restricted to the contralateral side. Unilateral transection of the facial nerve extinguished contralateral vibrissal responses, while ipsilateral vibrissae began to respond within 4 min. This abnormal response (primary change) was transient and gradually disappeared within hours to days. Instead, contralateral movements of forepaw and eye/eyelid muscles could be evoked from increasing portions of the former vibrissal field (secondary change), in which many points became unresponsive. After 4 days, the former vibrissal field had shrunk to a small central part, where ipsilateral vibrissae responsiveness remained. The secondary modification was stable for at least 2 weeks. Since the primary change is rapid, transient and may be mimicked by picrotoxin, it may be based on disinhibition of commissural connections, while the secondary change is longlasting and therefore may include some form of reorganization of associational synapses.

Animals↗
PubMed2006

Comparison of the inhibitory and excitatory effects of ADHD medications methylphenidate and atomoxetine on motor cortex.

Stimulant and norepinephrine (NE) reuptake inhibitor medications have different effects at the neuronal level, but both reduce symptoms of attention deficit hyperactivity disorder (ADHD). To understand their common physiologic effects and thereby gain insight into the neurobiology of ADHD treatment, we compared the effects of the stimulant methylphenidate (MPH) and NE uptake inhibitor atomoxetine (ATX) on inhibitory and excitatory processes in human cortex. Nine healthy, right-handed adults were given a single, oral dose of 30 mg MPH and 60 mg ATX at visits separated by 1 week in a randomized, double-blind crossover trial. We used paired and single transcranial magnetic stimulation (TMS) of motor cortex to measure conditioned and unconditioned motor-evoked potential amplitudes at inhibitory (3 ms) and facilitatory (10 ms) interstimulus intervals (ISI) before and after drug administration. Data were analyzed with repeated measures, mixed model regression. We also analyzed our findings and the published literature with meta-analysis software to estimate treatment effects of stimulants and NE reuptake inhibitors on these TMS measures. There were no significant pretreatment differences or effects of treatment order. Both agents produced a significant increase in facilitation and a decrease in inhibition. Effects of ATX and MPH did not differ significantly. Pooled estimates from published studies show similar results for stimulants and NE reuptake inhibitors. In conclusion, in healthy adults, both stimulant and nonstimulant medications for ADHD decrease cortical inhibition and increase cortical facilitation. Cortical inhibition, shown previously to be abnormal in ADHD, may play a key role producing behavioral pathology.

Adrenergic Uptake Inhibitors↗