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PubMed1984

[Activity of motor cortex neurons in the cat during a conditioned postural change reflex].

Spike activity of unitary motor cortex (area 4) neurons was recorded during performance of conditioned reflex postural adjustment in cats. Changes in activity of most neurons (increase of discharge frequency) correlated with conditioned-reflex supporting movement of the forelimb. These neuronal reactions had specific polycomponent patterns and preceded the conditional movements by 50-600 ms. Neuronal reactions connected with erroneous positive movement responses to differential stimuli and spontaneous "interstimular" movements had the same direction but were less intensive and occurred in most cases synchronously with these movements. Neuronal reactions and postural adjustments simultaneously disappeared during reflex extinction. The proposed method of elaboration of conditioned reflex of postural adjustments permits obtaining standard natural coordinated forelimb movements which form the necessary initial component of more complex behavioral reactions.

Animals↗

PubMedDate not supplied

The properties and possible mechanisms of interhemisphere synchronization in the motor cortex of the rat.

Cross-correlation analysis was used to observe interhemisphere synchronization of motor cortex neuron activity in anesthetized rats, which was seen on cross-correlograms as peaks located symmetrically relative to the coordinate origin. Peaks included "narrow" peaks (less than 20 msec) and "intermediate" peaks (30-80 msec). The results showed that the "common" source synchronizing the discharges of pairs of neurons located in different hemispheres of the brain might be a neuron (or group of neurons) located in one of the hemispheres and playing this role when there were reciprocal excitatory connections between it and each neuron in a pair. Comparison of the widths of symmetrical peaks with latent periods corresponding to transcallosal connections suggested that mono- and polysynaptic connections underlie the formation of "narrow" and "intermediate" peaks respectively.

Animals↗

PubMed1978

Dendro-dendritic and reciprocal synapses in the primate motor cortex.

Dendro-dendritic synapses have been observed infrequently in the deep layers of the motor cortex. The presynaptic dendrites are of a varicose type and themselves receive a considerable density of synapses both of the asymmetric and symmetrical type. The ultrastructure of the dendro-dendritic synapse itself shows the typical arrangement of presynaptic and postsynaptic membrane densities, often with presynaptic dense projections, and the membrane specialization is of the symmetrical type. There is the usual cleft containing electron-dense material between the presynaptic and postsynaptic profiles. The synaptic vesicles occur in a small cluster confined to a region close to the presynaptic membrane specialization; some of the vesicles are flattened and were shown by tilt analysis to be of the discoid type. Two examples were found of reciprocal dendro-dendritic synapses, both components being of the symmetrical type. A single axon terminal may make a synapse on to both dendrites involved in a dendro-dendritic synapse.

Animals↗

PubMed1997

Motor cortex lesions do not affect learning or performance of the eyeblink response in rabbits.

The possible modulatory role of motor cortex in classical conditioning of the eyeblink response was examined by ablating anterior neocortex in rabbits and training them with an auditory conditioned stimulus (CS) and an airpuff unconditioned stimulus (US) in either a delay (Experiment 1) or a trace (Experiment 2) conditioning paradigm. Topographic measures such as amplitude and onset latency were assessed during conditioning sessions for conditioned responses (CRs) and on separate test days for unconditioned responses (URs) by using a range of US intensities. No lesion effects were observed for learning or performance measures in acquisition or retention of either delay or trace conditioning. During trace conditioning, lesioned rabbits did, however, exhibit a trend toward impairment and demonstrated significantly longer CR latencies. Damage to motor and frontal cortex does not significantly affect eyeblink response performance or learning in either a delay or a trace conditioning paradigm.

Acoustic Stimulation↗

PubMed1981

Corticostriate projections from the primary motor cortex in the dog.

Corticostriate projections from the hindlimb and forelimb areas of the primary motor cortex in the dog were traced using the autoradiographic technique. Injections of tritiated leucine into the hindlimb area resulted in discrete oval or semicircular patches of label confined to the dorsolateral corner of the head and body of the caudate nucleus. No label was found over the putamen. Injections into the forelimb area yielded irregularly shaped patches of label over the dorsolateral part of the head and body of the caudate nucleus as well as more diffuse label over the dorsal-most part of the putamen. In both instances diffuse terminal fields were noted in the dorsolateral part of the contralateral caudate nucleus. A comparison of results in the caudate nucleus indicates that projections from the forelimb area terminate somewhat more caudally and slightly more ventrally and medially than do projections from the hindlimb area. The results further suggest that although terminal fields from these areas may to some extent interdigitate with one another, they also overlap each other to a significant degree.

Animals↗

PubMed2001

Task-dependent control of human masseter muscles from ipsilateral and contralateral motor cortex.

Corticotrigeminal projections to human masseter motoneuron pools were investigated with focal transcranial magnetic stimulation (TMS). Responses in left and right masseter muscles were quantified from the surface electromyogram (EMG) during different biting tasks. During bilateral biting, TMS elicited motor evoked potentials (MEPs) in both masseter muscles. On average, the MEP area in the masseter contralateral to the stimulus was 39% larger than in the ipsilateral muscle, despite comparable pre-stimulus EMG in both muscles. MEPs elicited while subjects attempted unilateral activation of one masseter muscle were compared with those obtained in the same muscle during a bilateral bite at an equivalent EMG level. MEPs in the masseter contralateral to the stimulated hemisphere were significantly smaller during unilateral compared with bilateral biting. There was no significant difference in the size of ipsilateral MEPs during ipsilateral and bilateral biting. We conclude that the corticotrigeminal projections to masseter are bilateral, with a stronger contralateral projection. The command for unilateral biting is associated with a reduced excitability of corticotrigeminal neurons in the contralateral, but not the ipsilateral motor cortex. We suggest that this may be accomplished by reduced activity of a population of corticotrigeminal neurons which branch to innervate both masseter motoneuron pools.

Adult↗

PubMed1985

Lateral spread of neuronal activity within the motor cortex investigated with intracellular responses to distant epicortical stimulation.

Lateral spread of activity within the motor cortex was examined by means of analyses of the direct cortical responses (DCRs) and intracellular responses to distant epicortical stimulation (EPICS) using cat encéphale isolé preparations. DCRs to the EPICS at a distance of 1.5-6.5 mm consisted of initial small positive (Pd) and subsequent negative waves (Nd). The reversal of polarity in depths occurred at 400-550 microns for Pd and at 150-250 microns for Nd as well as for the initial negative wave elicited by near EPICS. Intracellular responses to distant EPICS consisted of excitatory (EPSP) and inhibitory postsynaptic potentials (IPSP), disfacilitation (DF), and disinhibition (DI). Depth distributions of cells with EPSPs at two peaks in laminae II and V-VI, with IPSPs mainly in lamina III, and with DF or DI in laminae V-VI were the same with those by near EPICS. The inhibitory effects of distant EPICS on middle layer cells were much greater than those by near EPICS. No linear relations of the latency of EPSPs or IPSPs to the depth were seen for distant EPICS. Instead, the latency increased in proportion to the lateral distance in EPSPs at a slower rate than in IPSPs compared in superficial and middle layer cells. Several routes for lateral spread of activity were postulated. Most conspicuous are the excitatory route via horizontal axons in lamina I and the inhibitory route via laterally running axons in laminae II-III, which produce overall excitation of superficial layer cells and depression of middle and deep layer cells. Their possible role in phasic cortical arousal was discussed.

Animals↗

PubMed2002

Reproducibility of primary motor cortex somatotopy under controlled conditions.

BACKGROUND AND PURPOSE: The somatotopic organization of the contralateral primary motor cortex (M1) and its intra- and intersubject reproducibility has been the subject of many investigations and controversies. A potential explanation for a least some of the conflicting results could be the lack of movement control in the studies performed. The purpose of this study was to investigate these issues under controlled experimental conditions. METHODS: Functional MR imaging was performed in 12 healthy volunteers performing hand, finger, wrist, elbow, foot, and tongue movements. Two experimental sessions were separated by 2 weeks. Controlled conditions were achieved by means of a custom-designed arm and hand manipulandum providing standardization of the movements within and across subjects. RESULTS: The experiments revealed a clear large-scale somatotopy of the contralateral M1 with distinct subregions controlling the foot, arm, and tongue. Despite considerable overlap of the volumes, geometric centers of gravity (COGs) showed statistically significant differences in coordinates between the elbow, wrist, fingers, and hand. COGs showed a high degree of intra- and interindividual reproducibility, particularly for the upper limb movements, in contrast to the activation volumes that proved to be unreliable parameters, despite the controlled conditions. CONCLUSION: These findings support the existence of a gross-scale somatotopic organization yet also demonstrate a clear, fine-scale somatotopy of the within-arm representations. Furthermore, they reveal high reproducibility of the COGs when standardized conditions are applied. This observation highlights the need for movement control to allow for intra- and intersubject comparison.

Adult↗

PubMed1991

Electrophysiological and morphological properties of rat motor cortex neurons in vivo.

This paper describes results obtained from intracellular recordings and stainings of motor cortex neurons in the rat in vivo. Rats were anesthetized with phenobarbital. Neurons were intracellularly recorded with micropipettes filled with K+-methylsulphate + 4% HRP in phosphate buffer (pH 7.4). Successful recordings and stainings were obtained from 31 neurons. Intracellular recordings were distinguished as either intrasomatic or intradendritic. Action potentials (APs) recorded from somata were distinguished by their fast hyperpolarizing afterpotential from those recorded within dendrites. Dendritic APs were broader and often followed by an afterdepolarization. The firing patterns elicited by depolarizing current pulses allowed to distinguish 3 groups of neurons. (a) Group A neurons with a moderate firing-rate of up to 17 APs during a 100 ms depolarizing current pulse of 3.5 nA comprised small and large pyramidal cells and one aspiny multipolar neuron, probably a large basket neuron. (b) Group B neurons generated bursts, which either occurred spontaneously or during low intensity current injection. These neurons were classified as small pyramidal neurons and spiny star cells. (c) Group C neurons had a firing rate 3 times as high as group A neurons. These neurons were small aspiny cells with radial dendritic fields, which were classified as local interneurons. Intradendritic recordings were characterized by the occurrence of broad APs, most likely generated within the dendritic tree. Intracellular current injections produced burst-like potentials consisting of several APs with different amplitude and duration. In 3 penetrations of one apical dendrite up to 4 neurons were stained. In these recordings APs activated by intracellular current injection were particularly broad (up to 40 ms). The results suggest that neuronal firing patterns observed in in-vitro neocortical slices are also observed in in-vivo conditions.

Action Potentials↗

PubMed1990

Laminar interactions in rat motor cortex during cyclical excitability changes of the penicillin focus.

Laminar interactions between neurons in rat motor cortex during cyclical seizure episodes in the penicillin focus were studied using a combination of current source-density (CSD) and principal component analysis (PCA), combined with computer-based physical modeling. These data suggest that all phases of cyclical seizure phenomena are produced by interactions between two distinct populations of neurons, the same neuronal circuits previously reported to give rise to the direct cortical response (DCR) and electrically evoked interictal penicillin spikes (EIIS). The first population consists of small pyramidal cells in the supragranular layer, and the second population consists of larger pyramidal cells in the infragranular layers with apical dendrites extending to the cortical surface. The supragranular cells serve as a trigger zone for initiating both spontaneous interictal spikes (IIS) and polyspike bursts (PSB) during seizures. Fast activity in the supragranular cells is typically followed by a hyperpolarizing slow wave that may be the result of Ca2+-activated K+ currents. This slow wave increases during seizures, possibly reflecting changes in extracellular Ca2+ associated with seizure onset and termination. The monophasic response of infragranular cells is similar for both IIS and PSB and consists of a large depolarizing shift followed by a rapid but partial repolarization period and a subsequent gradual repolarization period lasting several hundred milliseconds. The infragranular response is similar in polarity and morphology to the intracellularly recorded paroxysmal depolarization shift (PDS) and may indicate that these deeper neurons are mainly responsible for this phenomena in neocortex. Finally, there is a marked postictal slow oscillation between the supra- and infragranular layers. This oscillation appears first and largest in the supragranular cells and may reflect a disturbance in excitatory feedback in these cells produced by the disinhibitory effect of penicillin, a disturbance capable of pathologically synchronizing the epileptic neuronal aggregate sufficiently for activation of the spike-generating mechanism and subsequent seizures.

Animals↗

PubMed1971

The short-latency projection from the baboon's motor cortex to fusimotor neurones of the forearm and hand.

1. The corticospinal connexions that are responsible for the firing of fusimotor impulses at short latency in response to brief, high-frequency stimulation of the baboon's motor cortex have been investigated by micro-electrode recording from antidromically identified fusimotor neurones of the forearm and hand.2. Of nineteen fusimotor neurones investigated by intracellular recording, six showed EPSPs at monosynaptic latency.3. In extracellular records, the latency of firing of an early fusimotor impulse was always too long to be explained by monosynaptic excitation by the corticospinal D volley, but could be explained by monosynaptic excitation from an I volley.4. Four of the nineteen intracellularly recorded fusimotor neurones showed short-latency (?disynaptic) IPSPs in response to brief high frequency cortical bursts.

Action Potentials↗

PubMed2006

Proactive interference as a result of persisting neural representations of previously learned motor skills in primary motor cortex.

Learning to control movements in different dynamic environments is marked by proactive interference; learning a first skill interferes with the subsequent learning of a second one. The neural basis of this effect is poorly understood. We tested the idea that proactive interference results from persisting neural representations of previously learned skills in the primary motor cortex (M1). We used repetitive transcranial magnetic stimulation (rTMS) of M1 to disrupt retention of a recently learned motor skill. If interference results from the retention of this skill then its disruption should be associated with reduced interference. Subjects reached to targets while interacting with a robotic arm that applied force fields to the limb. Fifteen minutes of 1-Hz rTMS to M1 impaired the retention of a first force field, and more importantly, reduced proactive interference when subjects learned a second one. Our findings suggest that retention and interference are linked at the level of M1.

Algorithms↗

PubMed2003

Preparatory activity in motor cortex reflects learning of local visuomotor skills.

In humans, learning to produce correct visually guided movements to adapt to new sensorimotor conditions requires the formation of an internal model that represents the new transformation between visual input and the required motor command. When the new environment requires adaptation to directional errors, learning generalizes poorly to untrained locations and directions, indicating that such learning is local. Here we replicated these behavioral findings in rhesus monkeys using a visuomotor rotation task and simultaneously recorded neuronal activity. Specific changes in activity were observed only in a subpopulation of cells in the motor cortex with directional properties corresponding to the locally learned rotation. These changes adhered to the dynamics of behavior during learning and persisted between learning and relearning of the same rotation. These findings suggest a neural mechanism for the locality of newly acquired sensorimotor tasks and provide electrophysiological evidence for their retention in working memory.

Animals↗

PubMed1995

[Excitability of motor cortex with transcranial magnetic double stimulation in the intact man].

To evaluate the excitability of central motor tract, we studied a transcranial magnetic double stimulation with short conditioning-test (C-T) interval of 1-10ms in eight normal volunteers. In addition, H-reflex of the forearm muscle was used to study the effect of the magnetic cortical conditioning stimulus on alpha-motoneuron, and the test response evoked by electrical cortical stimulation was also used to examine the effect of the magnetic cortical conditioning stimulus. The subthreshold conditioning and suprathreshold test stimuli were applied, and compound muscle responses were recorded in the relaxed abductor pollicis brevis muscle. There was a decrease of the test response size by the conditioning stimulus at C-T interval of 1-5ms. This attenuation was probably caused by intracortical inhibition. Because the identical magnetic cortical conditioning stimulus produced increase in H-reflex size. Moreover, the test response evoked by electrical cortical stimulus was not suppressed by the magnetic cortical conditioning stimulus; whereas, response evoked by the magnetic cortical test stimulus was suppressed at C-T intervals of 2ms. With the technique of transcranial magnetic double stimulation, therefore, it is possible to evaluate the inhibitory function in the motor cortex. The technique may be of use for pathophysiology, diagnosis and estimation of treatment in the diseases.

Adult↗

PubMed1991

Minimal stimulus parameters and the effects of hyperpolarization on the induction of long-term potentiation in the cat motor cortex.

The aim of the research program of which the present work is a part is to understand the neural mechanisms involved in motor learning and memory. One of the mechanisms postulated to be involved in this process is the induction of long-term potentiation (LTP) in the motor cortex. LTP can be induced in motor cortical neurons by tetanic stimulation of their afferents from the somatosensory cortex. In the present study, the effects of different stimulating parameters on the induction of LTP were examined, using in-vivo, intracellular recordings from anesthetized cats. The expression of LTP was documented by measuring the amplitude and rise-time of excitatory postsynaptic potentials (EPSPs) before and after tetanic stimulation. The minimal tetanic stimulation capable of systematically inducing LTP was found to consist of a train of stimuli at 50 Hz, 5 s. Shorter trains of stimulation produced only a short-lasting, transient potentiation. In different cells, identical stimulation parameters resulted in different degrees of potentiation of synaptic responses. Following all the stimulation trains examined, EPSP amplitudes were transiently depressed before reaching potentiated levels. The duration of this depression was directly correlated with the duration and the frequency of the tetanic stimulation. In all the cells in which LTP was induced, the variability in the amplitudes of potentiated EPSP was significantly greater than that of control EPSP amplitudes. Hyperpolarization of the postsynaptic cell, during the delivery of the tetanic stimulation, inhibited the induction of LTP. These phenomena are discussed in relation to the postulated mechanisms of LTP induction in the cortex.

Afferent Pathways↗

PubMed2002

Somatotopy in the ipsilateral primary motor cortex.

Conflicting reports exist about the occurrence, reliability and localization of activation in the ipsilateral primary motor cortex (M1). We re-examined this issue with functional magnetic resonance imaging in 12 volunteers performing right hand, finger, wrist, elbow, foot and tongue movements in two separate sessions. Ipsilateral M1 activation was inconsistently and non-reliably present during all movements: in 54% of all hand, 50% elbow, 46% finger, 33% wrist, and in 17% of all foot experiments. When compared to contralateral M1, the volumes and maximum t-values were always smaller. The ipsilateral M1 body representation was somatotopically organized with coordinates similar to the contralateral M1. Finally, the presence of ipsilateral M1 activation depended on the global activation level in other motor-related areas, which was significantly increased, when ipsilateral M1 activation was detected.

Adult↗

PubMed2001

Comparison of descending volleys evoked by monophasic and biphasic magnetic stimulation of the motor cortex in conscious humans.

The descending spinal volleys evoked by monophasic and biphasic magnetic stimulation of the motor cortex were recorded from a bipolar electrode inserted into the cervical epidural space of four conscious human subjects. The results suggest that both phases of the biphasic pulse are capable of activating descending motor output. The pattern of recruitment of descending activity depends on the intensity of the stimulus and the relative threshold of each volley to each direction of current flow.

Adult↗

PubMed1990

An output zone of the monkey primary motor cortex specialized for bilateral hand movement.

We have identified a subregion in the monkey primary precentral motor cortex (MI) that is characterized by its relationship to bilateral or ipsilateral hand movements. The subregion is located between the digit and face representation areas. The majority of single cells in this portion of MI exhibit distinct activity before and during visually triggered key-press movements performed by means of ipsilateral or contralateral digit flexion. Intracortical microstimulation evoked responses of ipsilateral, in addition to contralateral, digit muscles.

Animals↗