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At least 19 recordsLinked to original sources
PubMed1991

Magnetic stimulation of motor cortex and motor roots for painless evaluation of central and proximal peripheral motor pathways. Normal values and clinical application in disorders of the lumbar spine.

Magnetic stimulation of the motor cortex, motor roots, and proximal nerve trunks was performed in 46 healthy adults and in 73 consecutive patients with disorders of the lumbar spine. In combination with neurography and F-wave recordings, the fractionated stimulation of the motor pathways allowed calculation of conduction times of the pyramidal tract fibers, of the motor roots (ie, caudal fibers), and of the motor fibers of the lumbosacral plexus. Normal values for motor conduction times to the quadriceps, anterior tibial, and extensor digitorum brevis muscles were established. Patients had clinical and radiologic diagnoses of spinal stenosis (n = 43) and nerve root compression syndromes (n = 30). Motor conduction times to lower limb muscles were significantly delayed (above mean normal value +/- 2 x SD) in 65% of the patients with spinal stenosis and 50% of the patients with nerve root compression syndromes. Conduction slowing could be localized within the motor root and caudal fiber segment of the motor pathways in 80% of the patients in whom F-waves could be recorded. This method can be used to verify, quantify, and locate lesions of the motor pathways in conditions such as compression of the spinal cord, the caudal fibers (spinal stenosis), or the motor root passing through the intervertebral canal.

Adult↗
PubMed1985

Modification of the projection from the sensory cortex to the motor cortex following the elimination of thalamic projections to the motor cortex in cats.

Examination of the projection from area 2 of the sensory cortex to the motor cortex revealed substantial changes following lesion of the ventrolateral nucleus of the thalamus. These observed changes were as follows. (1) The polarity of the evoked potentials elicited by area 2 stimulation reversed in the depth of the motor cortex whereas in normal animals, there was no reversal. (2) The amplitude of area 2-elicited EPSPs in the motor cortical neurons became greater following the lesion of VL. (3) The shape of the observed EPSPs was characterized by multiple peaks whereas in normal animals, the EPSPs were generally smooth and monophasic. (4) Neurons receiving a short-latency input from area 2 were distributed throughout the depths of the motor cortex whereas in normal animals, they were located only in the upper layers (layers II and III). (5) Intracellular injection of HRP revealed that the neurons receiving short-latency input were not restricted to typical stellate type cells, but also included bipolar or bitufted neurons with elongated cell bodies and polarized arborizations. These neurons were located in the superficial (II and III) as well as in the deep (V) layer. It is concluded that the elimination of thalamic input resulted in the reinforcement of the corticocortical input to the motor cortex. The subsequently observed corticocortical projection extended to neurons did not originally innervated by the association fibers. The results suggested that functional recovery following thalamic lesion is partly due to reorganization of projections from the sensory cortex to the motor cortex.

Animals↗
PubMed1991

The striatum and motor cortex in motor initiation and execution.

The participation of striatal and motor cortex neurons in motor initiation and execution was studied using single neuronal recording in 3 monkeys performing wrist flexion and extension stimulus-initiated reaction time tasks. Observations of 46 striatal neurons whose activity correlated with the tasks were compared to recordings of 59 task-related motor cortex neurons. Neurons were classified as best related to the appearance of the go signal, movement onset, agonist or antagonist electromyographic changes, or the movement reaching target. Timing of neuronal activity changes in both striatum and motor cortex suggested that go signal-related neurons represent input function while most movement onset-related neurons represent output function. In the striatum, those related to reaching target represent output function. Furthermore, go signal-related neurons usually change activity before movement onset-related neurons which change activity prior to target attainment-related neurons. These observations suggest a hierarchical organization within the striatum and motor cortex. Also the striatum participates in programming target acquisition as well as motor initiation.

Animals↗
PubMed1987

Reorganization of the projection from the sensory cortex to the motor cortex following elimination of the thalamic projection to the motor cortex in cats; Golgi, electron microscope and degeneration study.

Changes of terminal connections of projection fibers from area 2 of the sensory cortex to the motor cortex following chronic lesion in the thalamus were examined using the electron microscope. The lesioned areas included nucleus ventralis anterior, n. ventralis lateralis and rostral part of n. ventralis posterolateralis. The synaptic sites were identified using the Golgi impregnation method to identify postsynaptic neurons in the motor cortex and the axonal degeneration method to identify presynaptic terminals of fibers originating from area 2. The following results were obtained. (1) The number of degenerating terminals per unit area in the motor cortex was increased to nearly twice that in normal animals. (2) The number of degenerating terminals synapsing with stellate cells was not increased but stayed more or less the same as in normal animals. (3) The number of degenerating terminals contacting pyramidal cells increased substantially, to more than twice that in normal animals. (4) These newly formed synapses were found on proximal dendritic shafts of the pyramidal cells in both layers III and V, suggesting that these synapses occupied the spaces where the thalamocortical terminals were located. (5) The functional significance of these newly formed synapses was discussed in relation to the recovery of motor function following thalamic lesion.

Animals↗
PubMedDate not supplied

Red nucleus and motor cortex: parallel motor systems for the initiation and control of skilled movement.

This study examines the differential contributions of motor cortex (MCx) and red nucleus (RN) neurons to the initiation of a targeted limb response and to the control of trajectory. These questions were assessed in two ways. First, by comparing the characteristics of task-related neuronal activity in MCx and RN. Second, by determining the changes in reaction time and trajectories produced by the reversible inactivation of corticospinal fibers in the crus cerebri (CSTc), the rubrospinal tract (RST) and the RN, using microinjections of lidocaine, gamma-aminobutyric acid, or muscimol. Neurons in forelimb areas of both MCx and RN were modulated in advance of forelimb force production. RN neurons more frequently had a phasic discharge pattern, while neurons in MCx more frequently had a tonic pattern. Whereas the modulation of most forelimb area neurons in MCx correlated with responses in a specific direction, the majority of RN neurons were non-directional. Reversible inactivation of CSTc, RN and RST prolonged reaction time. The normal stereotyped form of isometric force trajectories was unaffected by injections at any site. While CSTc inactivation resulted in hypometric responses, response amplitude was unchanged during RN and RST inactivation. We conclude that both MCx and RN contribute to response initiation, but that only MCx is involved in the proper scaling of targeted responses.

Animals↗
PubMed1985

Anatomical and physiological properties of the projection from the sensory cortex to the motor cortex in normal cats: the difference between corticocortical and thalamocortical projections.

Details of the distribution of terminal sites of the projection fibers from area 2 of the sensory cortex to the motor cortex were studied and compared with the distribution of terminals from the ventrolateral (VL) nucleus of the thalamus to the motor cortex. The results obtained were as follows: Intracortical microstimulation (ICMS) in area 2 produced measurable short-latency EPSPs only in neurons located in layers II and III of the motor cortex, whereas VL stimulation produced short-latency EPSPs in neurons throughout the depths of the motor cortex. The time from the beginning to the peak of the EPSPs was not significantly different for area 2- and VL-elicited EPSPs suggesting that there was no systematic difference between effective terminal sites for both inputs. However, there was a difference when a given neuron received both inputs suggesting that there was a segregation between the two inputs within a given cell. The majority of area 2-elicited EPSPs were smooth and monophasic, but some (40%) of them showed double peaks indicating that some neurons received mono- and disynaptic inputs from area 2. Intracellular injections of HRP suggested that neurons receiving input from area 2 were predominantly multipolar non-pyramidal neurons in layers II and III whereas neurons receiving thalamic input were pyramidal as well as non-pyramidal cells. Field potentials in the motor cortex evoked by area 2 stimulation did not change polarity in the depths of the cortex and therefore, differed from the VL-evoked potentials suggesting differences in the mechanisms of generating the electrical fields. It is concluded that association fibers effective for producing EPSPs terminate primarily on non-pyramidal cells in layer II and III whereas VL fibers terminate not only on pyramidal but also on non-pyramidal cells in layers III and V. This study provided a basis for examining the modifiability of association fibers after elimination of VL input to the motor cortex which is reported in the following paper.

Animals↗
PubMed1989

Physiological properties and patterns of projection in the cortico-cortical connections from the second somatosensory cortex to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons in the second somatosensory cortex (SII), and the pattern of projection of these neurons to area 4 gamma of the motor cortex in cat were studied by using single unit recording and collision techniques. Antidromically activated neurons were recorded along the anterior and posterior regions of the lateral bank of the anterior suprasylvian sulcus (ASSS) and from the middle part of the anterior ectosylvian gyrus (AESG) following weak intracortical microstimulation (ICMS) to area 4 gamma. Stimulation of the region around the activated neurons failed to produce muscle contraction or movement with currents of 30 microA or less. The majority of antidromically identified neurons received somatotopically organized afferent inputs from the skin on the contralateral side of the body. A small number of SII neurons received bilateral input. In 91% of the cases receptive field information was available for both the antidromically activated SII neuron and for neurons around the stimulating electrode in area 4 gamma. In 71% of these cases, both cortical sites were activated by sensory input from the same or adjacent peripheral area of the body. Neurons in the rostrocaudal region of the lateral bank of ASSS and the upper part of AESG (forelimb area) projected to the lateral cruciate gyrus of the motor cortex (forelimb area), while neurons in the ventrocaudal region of the medial part of AESG (hindlimb area) projected to the medial part of the postcruciate subregion of the motor cortex (hindlimb area). Antidromically activated SII neurons were typically found in layer III. These results suggest a topographically organized pattern of projection to the motor cortex from SII.

Animals↗
PubMed1992

Homotopic transplant of fetal cortex to lesioned motor cortex of adult rats. A comportamental and anatomical study.

Previous investigations have shown that the transplant of fetal nervous tissue in adult, formerly injured, brain induces an improvement of the neurological deficits. The process underlying this finding is not yet known. It has been proposed that this process is favourably supported by the reconstruction of the damaged circuitry, replacing the injured neurons with the transplanted fetal cells. In the present study we have investigated the relation between the improvement of the neurological deficits and the anatomical integration of the transplanted neurons within the host brain. The plan of the investigation included two steps: the first step consisted of inducing neurological deficits by kainic acid lesion of the motor cortex and then studying the changes in the motor learning following a homotopic transplant of fetal cortex in the side of the lesion. The second step consisted of studying the anatomical integration of the transplanted cortex with the thalamus of the host. The results showed that the rats with injury of the motor cortex followed by solid transplant of fetal cortex (E 17) had a significantly greater recovery of the motor learning with respect to non-transplanted rats with a lesioned motor cortex. In the same rats, the connections between the transplanted cerebral cortex and the thalamus of the host has been investigated. WGA-HRP solution was injected in the thalamus and both labeled fiber terminals and labeled cells were searched for in the transplants. The results showed that: 1) the host thalamus projects to the transplanted cortex with a lower density than to the host cortex surrounding the transplant; 2) the thalamic projection to the host cortex is topographically organized, whereas the projection to the transplant is arranged in patches without any topographical organization; 3) the transplant does not send a significant projection to the thalamus of the host. In conclusion, the experimental findings demonstrate that the reconstruction of an injured thalamo-cortical circuitry of adult rats transplanting fetal neurons is not possible. The improvement of the functional deficits by the transplant of fetal tissue may be referred to aspecific factors enhancing the functional activity of the host cortex undamaged by the initial injury. The identification of the nature of the hypothesized factors requires further investigation.

Animals↗
PubMed1991

Transcranial stimulation of motor cortex in upper motor neurone syndrome: its relation to the motor deficit.

The purpose of this investigation was to clarify the functional significance of the fastest cortico-motoneuronal connections in chronic upper motor neurone syndromes. Using magneto-electrical stimulation of motor cortex the intactness of cortico-motoneuronal connections was assessed in 51 patients presenting with variable degrees of impairment. There was a gross correlation between clinical impairment of the patient and the degree of pathology of cortico-motoneuronal efferents. Covariation of clinical data with transcranial stimulation was better than covariation with the size of lesion on CT scans. In some patients, however, definite clinical impairment, especially affecting distal fractionated movements, was associated with completely normal responses. There was no evidence of response abnormality in distal muscles ipsilateral to the hemispheric lesion. The data indicate that motor deficit can exist in the presence of normal cortico-motoneuronal conduction times, showing that intactness of these connections is not a sufficient condition for preservation of voluntary motor activities. This underlines the importance of other pathways for the pathogenesis of upper motor neurone syndromes.

Adult↗
PubMed1988

Maturation of corticospinal tracts assessed by electromagnetic stimulation of the motor cortex.

The motor cortex can be excited in adults using electromagnetic stimulation, and the latency to the evoked muscle action potential allows an assessment of the integrity of corticospinal tracts. We applied this technique in children to describe the maturation of corticospinal tracts. The latency from cortical stimulation to the onset of the evoked muscle action potentials and the subject's height were recorded. The subject's height was divided by the latency to the onset of the evoked muscle action potential to provide an index of the conduction velocity within descending motor pathways (VI). It is possible to evoke muscle action potentials after electromagnetic stimulation of the motor cortex in children including preterm babies and there is a stepwise increase in the sensitivity to stimulation between 8 and 11 years of age. In addition there is a progressive increase in VI with age; adult values are attained at about 11 years. The successful application of this technique in children suggests that electromagnetic stimulation of the motor cortex has the potential to allow detection of abnormality in motor pathways in newborn babies and young children.

Adolescent↗
PubMed1992

Functional properties of single neurons in the face primary motor cortex of the primate. I. Input and output features of tongue motor cortex.

1. We have recently demonstrated that reversible, cooling-induced inactivation of the face motor cortex results in a severe impairment in the ability of monkeys (Macaca fascicularis) to perform a tongue-protrusion task but produces only relatively minor effects on the performance of a biting task by the same monkeys. To establish a neuronal correlate for these different behavioral relations, the present study has detailed the afferent input and intracortical microstimulation (ICMS)-defined output features of a population of face motor cortical neurons, and in a subsequent study we have documented the activities of the same population of neurons during the performance of the tongue-protrusion and biting tasks. 2. Of the 231 single neurons recorded within the face motor cortex, 163 were located at sites from which ICMS (less than or equal to 20 microA) could evoke tongue movements (i.e., "tongue-MI" sites) at the lowest threshold for eliciting orofacial movements. The remainder were located at sites from which ICMS evoked jaw movements ("jaw-MI" sites), face movements ("face-MI" sites), or at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 3. We confirmed the general organizational features of the face motor cortex that have been defined in previous studies, but we documented in detail the organizational features for tongue-MI. Thus we found that tongue movements were well represented, whereas jaw-closing movements were poorly represented; the representations for face, jaw, and tongue movements were overlapped; the same ICMS-evoked tongue movement could be multiply represented within tongue-MI; tongue-MI was characterized by a prominent input from superficial mechanosensory afferents, whereas there was little evidence for deep input; a close spatial match was found between ICMS-defined motor output and somatosensory afferent input for tongue-MI. 4. A variety of tongue movements could be evoked by ICMS at tongue-MI sites and were categorized into protrusion, retrusion, laterally directed, and other types of tongue movement. Low-threshold (i.e., less than or equal to 5 microA) ICMS-defined tongue-MI sites, which were considered to represent "efferent zones" projecting relatively directly to motoneurons, were reconstructed three dimensionally to provide insights into the spatial organization of tongue-MI. Examples of each of the four low-threshold efferent-zone categories were usually found throughout the ICMS-defined tongue-MI without any apparent preferential distribution. Furthermore, different low-threshold efferent-zone categories had close spatial relationships to each other in cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Responses of cat motor cortex neurons to cortico-cortical and somatosensory inputs.

Intracellular techniques were used to investigate a cortico-cortical path from sensory cortex to motor cortex of cats. Cortico-cortical epsps were evoked in motor cortex neurons by microstimulation of area 3a. Epsps with latencies between 1.2 and 2.4 ms were identified as monosynaptic. These short latency cortico-cortical effects were recorded in layers II through VI of the motor cortex. Neurons with monosynaptic cortico-cortical epsps also received excitatory inputs from forelimb nerves, usually from both muscle and cutaneous afferent fibers. The epsps evoked from forelimb nerves in motor cortex neurons were preceded by neural activity in somatosensory cortex. Time delays between arrival of inputs in sensory cortex and in motor cortex were compared to the latencies of cortico-cortical epsps in the same motor cortex neurons. It was apparent that the timing was appropriate for the identified cortico-cortical path to have relayed some sensory inputs to motor cortex.

Animals↗
PubMed1987

Transcranial stimulation of the motor cortex to produce motor-evoked potentials.

Monitoring of the nervous system using evoked potentials is a developing tool. A new evoked potential, the motor-evoked potential (MEP), based on a traditional test, uses brain stimulation to monitor the motor system. The MEP complements the existing modalities, which are wholly sensory. The MEP can be prompted by direct stimulation of the motor cortex, but, in a more general way, by transcranial stimulation. Electric or magnetic means can be used. One electric system involves placement of an electrode on the scalp over the motor cortex, paired with a cathodal plate on the roof of the hard palate. Recording electrodes are placed over the spinal cord, peripheral nerves, and muscles. Signals are recorded with a standard, evoked-potential, signal-averaging computer. Animal studies indicate that the electric stimulus activates primarily the pyramidal system to produce a descending evoked potential in the ventral and dorsolateral spinal cord. It is more sensitive than the sensory-evoked potential to spinal cord injury produced by the weight-drop method in cats. The peripheral nerve responses, much more sensitive to injury than the cord responses, can be altered by metabolic abnormalities. To date, the MEP has been an accurate indicator of ambulation in chronic spinal cord injury in animals. Parallel clinical development in the operating room has shown that the test is valuable; and it monitors brainstem or cortex manipulation, as well as cord manipulation. Safety studies are encouraging. The MEP is developmentally and technically demanding, but it has produced high quality signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Changes in dry weight of pyramidal cell nuclei in the motor cortex during local motor-food conditioning.

The formation of a local motor-food conditioned reflex in rats, consisting of pressing on a level with the unpreferred paw, in one session led to a decrease in dry weight of the large pyramidal cell nuclei in the area of representation of that paw in the motor cortex. Frequent repetition of the local motor-food conditioned reflex consisting of pressing on the level with the preferred paw was not accompanied by any such changes. It is suggested that changes in dry weight of the large pyramidal cell nuclei in the area of representation of the unpreferred paw are due to involvement of these neurons in the formation of the new motor coordination (the local conditioned reflex).

Animals↗
PubMed1988

Noninvasive mapping of human motor cortex.

Human motor cortex was stimulated using brief, high-voltage electrical stimulation. Constant-voltage stimuli were delivered through a bipolar surface stimulator with the anode placed at multiple positions on the scalp and the cathode situated 2.5 cm anterior to the anode. Recordings were bilateral from the abductor pollicis brevis, tibialis anterior, and risorius. We averaged the amplitudes of three muscle responses obtained from stimulation of each scalp position and assigned the resultant value to that position. The findings in eight normal volunteers were similar and reproducible. The maximal responses of the right hand were obtained when stimulating over C3, of the left hand when stimulating over C4, of the right and left legs when stimulating over Cz, and of the right side of the mouth when stimulating over T3.

Adult↗
PubMed1988

Rapid reorganization of adult rat motor cortex somatic representation patterns after motor nerve injury.

The potential for peripheral nerve injury to reorganize motor cortical representations was investigated in adult rats. Maps reflecting functional connections between the motor cortex and somatic musculature were generated with intracortical electrical stimulation techniques. Comparison of cortical somatotopic maps obtained in normal rats with maps generated from rats with a facial nerve lesion indicated that the forelimb and eye/eyelid representations expanded into the normal vibrissa area. Repeated testing from an electrode placed chronically in the motor cortex showed a shift from vibrissa to forelimb within hours after facial nerve transection. These comparatively quick changes in motor cortex representation pattern suggest that synaptic relations between motor cortex and somatic musculature are continually reshaped in adult mammals.

Animals↗