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PubMed1978

Postnatal development of visually evoked activity within motor cortex of cat.

1. The development of visually evoked activity within motor cortex was studied in chloralose-anesthetized kittens of 3, 4, and 5 mo of age and adult cats. 2. The slow-wave response from motor cortex of the adult cat is a triphasic negative-positive-negative wave. In 3-mo-old kittens the response is only a long-duration negative wave, while at 4 mo the positive and late negative waves emerge, and at 5 mo of age the adult form of the response is present. 3. Single neurons in the adult respond to the light during the positive component of the slow-wave response. When only the negative wave is present in kittens of 3 and 4 mo of age, neurons do not respond to the photic stimulus. At 5 mo of age the correlation between unit activity and the positive component of the response is identical to the adult. 4. The laminar analysis of the positive component of the response suggests that it originates relatively superficially in cortex and migrates down toward the deeper layers. Its correlation with unit activity indicates that the positive component represents excitatory postsynaptic potentials. 5. These results are consistent with an excitatory drive on neurons within motor cortex undergoing development change until the 5th mo of life.

Aging↗

PubMed1992

A frequency analysis of neuronal activity in monkey thalamus, motor cortex and electromyograms in wrist oscillations.

1. Extracellular recordings were made in three monkeys while recording from neurones in the motor cortex (eighty-four cells), ventro-posterior lateralis pars caudalis (VPLc, forty-two cells) and cerebellar thalamus (seventy-seven cells). 2. This experiment was designed to produce active and reflex movements of varying velocities in order to study the relationship between amplitude of velocity and magnitude of neuronal discharge of thalamic neurones. The active movements were voluntary rapid alternating movements (RAMs) of the wrist and the reflex movements were produced by forcibly oscillating the wrist joint between frequencies of 1 and 7 Hz (forced oscillations). 3. This study was also designed to examine cerebellar influences on a reflex path, namely the transcortical reflex loop. Forced oscillations were predicted to provide circumstances where active damping was required to prevent excessive oscillations in the reflex path. Rapid alternating movements of the wrist were predicted to provide circumstances where oscillations at the natural frequency in that reflex path would support and propagate the movements. 4. Forced oscillations from 1 to 7 Hz produced movements of different velocities. VPLc and cerebellar thalamic neurones discharged in relation to the duration of movement in a particular direction, but their discharge levels were unrelated to the magnitude of the velocity. Motor cortex neurones fired in a pattern which was related to the timing but not the magnitude of the acceleration. 5. In forced oscillations of the wrist the resonant frequency was between 3 and 7 Hz. They may be controlled in part by a transcortical reflex. The cerebellar thalamic neurones did not fire before motor cortex neurones. Therefore, it is unlikely that the cerebello-thalamo-cortical pathway is necessary to damp these potentially unstable oscillations by an effect on antagonist-related cortical neurones. 6. Rapid alternating movements (RAMs) of monkeys' wrists were performed in a stereotyped fashion over a narrow range of frequencies with the greatest displacement in joint angle and peak velocity at the natural frequency of 3-5 Hz. 7. During the performance of RAMs, neuronal discharge modulated sinusoidally in the VPLc, cerebellar thalamus and motor cortex. There was no relationship between velocity and neuronal discharge of the cerebellar thalamic and motor cortical neurones but there did appear to be a relationship between velocity and VPLc neuronal discharge. 8. The onset of electromyogram (EMG) discharge changed earlier than neuronal discharge in the motor cortex and thalamus during the performance of RAMs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1979

Thalamic projections to the feline motor cortex studied with horseradish peroxidase.

Cells in the thalamus projecting to the distal forelimb regions of the motor cortex, area 3a, and the sensory cortex were identified with horseradish peroxidase (HRP). These cortical areas were defined by mapping evoked potentials from superficial and deep radial nerve stimulation. Following injections into the motor cortex, the labelled cells were distributed throughout a large region (greater than 2 mm wide) in the ventral portion of the ventral lateral nucleus (VL). The border area between VL and the ventral posterolateral nucleus (VPL) also contained labelled cells. The region containing labelled cells following injections into area 3a was in the rostral, dorsal VPL, and overlapped with the region containing cells labelled by injections into the motor cortex. Cells labelled by injections into the sensory cortex were near the center of VPL distinctly separated from those labelled after injections into either area 3a or the motor cortex.

Animals↗

PubMed1975

Functional significance of projection from the cerebellar nuclei to the motor cortex in the cat.

The functional organization of projections from the cerebellar subcortical nuclei to the motor cortex through the nucleus ventralis lateralis (VL) of the thalamus was studied using tungsten microelectrodes for stimulation and recordings in acute and chronic cats. The following results were obtained. (1) Microstimulation of a small area of the ventral thalamus produced contraction of a single limb muscle as well as movements of whiskers. (2) The stimulus parameters for producing low threshold contraction of limb muscles were different from those for face muscles. The decrease of the frequency gradualy increased the threshold values for face muscles whereas the decrease abruptly increased the threshold for limb muscles. The optimum duration of the train for the lowest thresholds was longer for face muscles. (3) Stimulation of cerebellar nuclei (interpositus and lateralis) produced contraction of limb muscles. The stimulus parameters for the minimum threshold were similar to those for producing contraction of limb muscles from the ventral thalamus. (4) The peripheral receptive fields of neurons located around the low threshold sites in the thalamus were diffuse, i.e. they were driven insecurely by twisting the joints or pressure to the deep structures, but could not be driven by touch or light pressure on a circumscribed area of the body. (5) Chronic ablation of the motor cortex did not abolish the muscle contractions produced by thalamic stimulation, excluding the possibility that the effects were produced by stimulation of the branches of the pyramidal tract fibers reaching the ventral thalamus. (6) Chronic section of the brachium conjunctivum abolished or changed the characteristics of the contractions produced by thalamic stimulation indicating that the previous effects were produced by stimulation of cerebellar efferent fibers reaching the thalamus. (7) From these results it was concluded that the efferent impulses originating from the cerebellar nuclei can produce contraction of a particular muscle through activation of the red nucleus. These impulses are, at the same time, transmitted to a small group of neurons in the VL and then forwarded to the neurons in the motor cortex. (8) The functional significance of the VL projection system has been discussed in relation to the efferent zones within the motor cortex.

Animals↗

PubMed1978

Projection from area 3a to the motor cortex by neurons activated from group I muscle afferents.

Two receiving areas in the pericruciate cortex are known for inputs from group I muscle afferents of forelimb nerves. One focus is near the postcruciate dimple of area 3a, and the other in the lateral sigmoid gyrus of the motor cortex (area 4gamma). The cortico-cortical projection of area 3a to 4gamma, and the relay by this projection of group I muscle afferent input to the motor cortex were investigated in cats. The following results were obtained. 1. Seventy-four neurons within area 3a were antidromically activated by intracortical microstimulation of the motor cortex. 2. Although excitation evoked by stimulation of group I muscle afferents could be demonstrated for only a few (8 of 48) cortico-cortical neurons in extracellular recordings, due to the methodological limitations discussed, this input evoked EPSPs in 8 of 9 cortico-cortical neurons recorded intracellularly. Therefore, it is likely that the majority of neurons projecting from area 3a to the motor cortex have an excitatory synaptic input from group I afferents. 3. Neurons projecting from area 3a to the motor cortex were most commonly found in cortical layer III, although some were found in layer V. 4. Five of nine pyramidal tract neurons of area 3a had a strong excitatory synaptic input from group I muscle afferents. 5. A new type of pyramidal tract neuron was found which has cortico-cortical axon collaterals connecting the two cytoarchitectonic regions. These various neurons may be part of a feedback system from muscle afferents to the motor cortex.

Afferent Pathways↗

PubMed1992

Area 3a in the cat. II. Projections to the motor cortex and their relations to other corticocortical connections.

It is well known that area 3a in the cat may monosynaptically influence the activity of neurons in the motor cortex. Much less information is available, however, on the anatomy of these connections. By using single or combined injections of different retrograde axonal tracers, we investigated the topography (horizontal and laminar) of area 3a neurons projecting to the motor cortex, and the anatomical relationships between these neurons and those projecting to other areas (2, 5, and SII) which, in turn, project to the motor cortex. Area 3a projects to all parts of area 4 gamma, to area 4 delta, and to the agranular area 6 in the lateral bank of the presylvian sulcus (area 6 alpha gamma), but not to other parts of areas 4 and 6. This projection exhibits a loose topographic organization along the mediolateral dimension of area 3a, and, in many cases, arises predominantly from the rostral half of this area. Although single small injections in the motor cortex produced two or more separate patches of retrograde labeling in 3a, after simultaneous injections of fluorochromes in two separate loci there often appeared in area 3a overlapping populations of neurons which were labeled retrogradely by each of the dyes, but with very few double-labeled neurons. In horseradish peroxidase (HRP) cases, 72% of area 3a neurons projecting to area 4 gamma were distributed in supragranular layers (mainly layer III), although the proportion of labeling in infragranular layers was larger when using fluorescent dyes. Double-labeled cells predominated in infragranular layers. These results have a bearing upon the functional roles that have been attributed to area 3a, as a cortical locus involved in muscle sensation, and a cortical relay to the motor cortex of rapid feedback information from muscle activity during movement.

Amidines↗

PubMed1992

Effects of preliminary perceptual output on neuronal activity of the primary motor cortex.

Observations of single neurons in the primary motor cortex of 1 monkey provided evidence that preliminary perceptual information reaches the motor system before perceptual analysis is complete. Neurons were recorded during a task in which 1 stimulus was assigned to a wrist flexion response and another was assigned to wrist extension. Two stimuli were assigned to a no-go response; each was visually similar to either the flexion or the extension stimulus. When a no-go stimulus was presented, neurons responded with weaker versions of the discharge patterns exhibited to the visually similar stimulus requiring a movement, suggesting that neurons receive partial perceptual information favoring that movement. Functionally separable neuronal populations were identified, and differences in the activations of these provide evidence about the functional effects of preliminary perceptual output on movement control processes.

Animals↗

PubMed1992

Sensory characteristics of monkey thalamic and motor cortex neurones.

1. Extracellular single-cell recordings were made from the cerebellar thalamus, the ventro-posterior lateralis par caudalis (VPLc) and motor cortex of three conscious monkeys. Recordings were made from the thalamus as well as the cortex in two monkeys. In all, recordings were made from the thalamus in four hemispheres and from the motor cortex in four hemispheres. The animals were trained to permit a detailed examination when relaxed. Unexpected perturbations were applied to the wrist. Seventy-seven wrist-related neurones were recorded in the cerebellar thalamus, forty-two neurones from the VPLc and eighty-four neurones in motor cortex. 2. Cerebellar nuclear stimulation was used to physiologically identify thalamic neurones receiving input from the cerebellum. The location of all neurones was verified histologically. 3. The majority of cerebellar thalamic neurones had deep sensory receptive fields related to a single muscle, a group of synergists or a single joint. There was a distinct topographical organization. These fields were similar to sensory fields in motor cortical neurones, but had higher thresholds. 4. VPLc neurones had discrete deep or cutaneous sensory fields, or a combination of these fields, which suggests convergence. VPLc neurones had fields with lower thresholds than cerebellar thalamic neurones. The somatotopically located forelimb area in the VPLc was posterior to and continuous with the forelimb area in the cerebellar thalamus. 5. VPLc neurones responded with a shorter latency to wrist perturbations than did cerebellar thalamic neurones. VPLc neurones with deep sensory fields changed firing significantly earlier than those with cutaneous fields. The VPLc is likely to be the major source of sensory input to the motor cortex, and based on the results of this study we suggest that the VPLc is the thalamic nucleus best placed to transmit short-latency afferent input from the forelimb. 6. The timing of the neuronal discharge of cerebellar thalamic and VPLc cells, which resulted from perturbations of the wrist, was best linked to the duration of movement rather than its amplitude. The cells began firing as soon as the velocity changed sign and continued firing until the sign of the velocity changed again. In subsequent corrective movements neuronal discharge in the VPLc appeared to also encode movement acceleration.

Animals↗

PubMed1992

Dendritic arbolization of large pyramidal neurons in the motor cortex of normal and reeler mutant mouse.

Reeler, an autosomal recessive mutation in mice, is characterized by abnormal positioning of the neurons in the cerebral cortex. We performed a descriptive analysis on the arborization of dendritic processes of large pyramidal neurons in the motor cortex (hindlimb area) of normal and reeler mice, as seen in the Golgi preparations. In the normal mouse, somata of large pyramidal neurons were located in the layer V, and their apical dendrites ascend vertically to the pial surfaces. Their basal dendrites proceed horizontally or inferiorly. In the reeler mouse, typical large pyramidal neurons with a normal (upright) apical dendrite and a variety of atypical large pyramidal neurons with a disoriented apical dendrite were radially scattered within the motor cortex. Typical large pyramidal neurons occupied the lower half of the motor cortex, whereas atypical large pyramidal neurons were predominantly observed in the upper half of the motor cortex. Atypical large pyramidal neurons were further divided into inverted, tumbled, V-shaped, bipolar and superficial polymorphic cells, as previously reported (Terashima et al., J. Comp. Neurol. 218:314-326, 1983). Superficial polymorphic cells localized in the layer of polymorphic cells and the layer of the large pyramidal cells were characterized by the extremely poor dendritic arborizations and the smooth surface of the dendrites, which suggests development of dendrites of these neurons was deranged by the reeler genetic locus.

Animals↗

PubMed1992

The contribution of magnetic stimulation of the motor cortex to the diagnosis of cervical spondylotic myelopathy. Correlation of central motor conduction to distal and proximal upper limb muscles with clinical and MRI findings.

Magnetic stimulation of the motor cortex and cervical spine was performed on 24 patients with cervical spondylotic myelopathy documented by MRI. Compound motor action potentials (CMAPs) were recorded from the biceps and thenar muscles to study the central motor pathways of two different myotomes, C5-C6 and C8-D1. Central motor conduction was abnormal in all 24 patients for thenar muscles and in 5 patients for biceps brachii. In patients with a single compression level, central motor conduction abnormalities were confined to the myotomes caudal to the site of compression documented by MRI, in both proximal and distal upper limb muscles in the patients with upper spondylotic compression, and in distal muscles only in the patients with lower compression. In the patients with multilevel compression, central motor conduction time was abnormal for thenar muscles and always normal for the biceps muscle, but its mean value was significantly greater than in the control subjects, suggesting a slight involvement of central motor pathways for proximal upper limb muscles and major damage of the lower cervical segments. Owing to their high degree of sensitivity, central motor conduction studies may be of considerable value in the functional assessment of central motor pathways in cervical spondylotic myelopathy.

Action Potentials↗

PubMed1976

[Transcallosal modulation of a focus of maximal activity in the motor cortex].

In cats, EPs from 170 symmetrical points of the motor cortex were recorded during bilateral and unilateral stimulation of nerves of hind--and forelimbs. Charts of localization of the maximal activity foce (MAF) were drawn. Transection of the corpus callosum was shown to be followed by narrowing of MAFs during bilateral stimulation and by their enlargement during unilateral stimulation. The effect of MAF enlargement was found to be due to summation of thalamocortical and transcallosal projections in animals with intact callosal system, while the MAF narrowing effect--to be determined by reciprocal transcallosal influences. Existence of the spatial transcallosal modulation of thalamocortical projection in the motor cortex is supposed.

Animals↗

PubMed1992

Magnetic stimulation of motor cortex in relation to fastest voluntary motor activity in neurologically asymptomatic HIV-positive patients.

Forty-two HIV-positive patients of various CDC stages without clinically evident neurological deficits were examined with transcranial magnetoelectrical stimulation (TMS). Cortical as well as cervical and lumbar root stimulation was performed after excluding peripheral neuropathies in comparison to an age- and sex-matched control group. Whereas central conduction times were normal, conduction between cervical or lumbar roots and muscle was prolonged. Results were correlated to those of a motor test battery, which revealed slowing of fast alternating movements similar to findings in extrapyramidal disorders. Data indicate that proximal parts of the peripheral nervous system and extrapyramidal structures are subclinically involved in early HIV infection whereas the fastest corticospinal projections remain intact.

Adult↗

PubMedDate not supplied

Correlation of neuronal cell body size in motor cortex and hippocampus with body height, body weight, and axonal length.

This study examined the comparative effects of body height and body weight on the neuronal cell size in humans and investigated their possible mechanisms. A total of 21 cases between the ages of 20 and 40 years were studied. Data on body height, body weight, and neuropathology were obtained from autopsy records. Mean cross sectional areas of cell bodies for 30 normal neurons were determined for the motor cortex projecting to lumbar spinal cord segments (L) 1-4 (Betz cells) as well as various regions of the hippocampus. Approximate axonal length of the motor neuron studied was measured from motor cortex to L2. We found that only motor cortex neuronal cell body size was significantly proportional to body height and the respective axonal length (p < .05). The findings indicate that: 1) body height has a greater effect than body weight on the motor neuron cell size, probably because of its association with axonal length; 2) the effect is regional (motor cortex) rather than general.

Adult↗

PubMed1978

Correlation of neural discharge with pattern and force of muscular activity, joint position, and direction of intended next movement in motor cortex and cerebellum.

1. Monkeys were trained to grasp a rod movable in a horizontal arc (Fig. 1), and to hold the rod by angulation of the wrist in each of three positions (A,B, C). A maintained load was placed on the rod alternately to oppose flexion and extension. At a light signal, the monkey had to move to the next position in a prescribed sequence (ABCBABCBA, ETC.). The task was designed to dissociate, while holding in position, the following variables: 1) pattern of muscular activity in the forearm required to hold the wrist in position, determined by the direction of the load (flexor or extensor muscles); 2) position of the rod, and thus angulation of the wrist joint (A, B, and C); and 3) set for the direction of the intended next movement (flexor or extensor). These variables are subsequently referred to as MPAT, JPOS, and DSET, respectively. 2. After training, recordings were made of the EMG activity of muscles used in the task and of the discharge of single neurons in the motor cortex of the cerebrum and the interposed and dentate nuclei of the cerebellum. 3. While holding the wrist in position, EMG and interpositus behaved uniformly, with higher discharge frequency under load in one direction and lower discharge frequency under load in the opposite direction. This relation was relatively independent of the position held and of the direction of the intended next movement. Thus, interpositus and EMG both seemed best related to the MPAT variable, as opposed to JPOS and DSET variables. By contrast, neurons in motor cortex and in dentate fell into three categories: one category discharged in relation to the pattern of muscular activity (MPAT), a second to the position of the wrist (JPOS), and a third to the direction of the intended next movement (DSET). While MPAT neurons formed a distinct dissociated group, neurons that were best related to JPOS were often related to DSET, and vice versa. 4. A few of the MPAT neurons in interpositus and motor cortex were further studied by varying the magnitude (as well as the direction) of the loads. Both interpositus and motor cortex MPAT neurons changed firing frequency in relation to the magnitude of load, and though few neurons were thus studied, the relation seemed clearer for interpositus than for motor cortex. 5. Anatomically, the three types of neurons thus classified by firing pattern during the hold periods were intermixed in the arm area of motor cortex. In dentate and interpositus, those neurons thus related to the performance were localized to a narrow strip across the posterior part of both nuclei. Neurons apparently related to eye and drinking movements were located more posteriorly still, suggesting somatotopic representation.

Animals↗

PubMed1976

Pyramidal cell abnormalities in the motor cortex of a child with Down's syndrome. A Golgi study.

The neuronal organization of the motor cortex of a 19-month old child with Down's syndrome (mongolism) has been studied with the rapid Golgi method. This congenital syndrome, also known as 21 Trisomy is caused by a chromosomal abnormality consisting of the presence of an extra chromosome in the group 21. Various structural abnormalities have been found in the dendritic spines (postsynaptic structures) of the pyramidal neurons of the motor cortex of this child. The axo-spinous synapses of these neurons are considered to be altered by these spine abnormalities. In addition, a peculiar form of intrinsic vacuolar change affecting the dendrites and scattered neuronal fragmentation and necrosis have also been found. At least three different types of abnormality involving the spines--(the unusually long spine, the very short spine and a reduction in the number of spines)--are recognized among the pyramidal cells of the motor cortex. It is postulated herein: that a basic anomaly, possibly related to the genetic disorder affects primarily some cortical neurons which undergo progressive degenerative changes terminating in cell fragmentation and death. The different spine abnormalities are considered to represent various developmental stages of the common genetic anomaly. These changes might be structural correlates of the motor incoordination and mental retardation which are characteristic of this genetic disorder, but, final conclusions should await the investigation of other cases with this or similar methods capable of demonstrating the normal as well as the abnormal structural organization of the human cerebral cortex.

Dendrites↗

PubMed1992

Anodal and cathodal stimulation of the upper-limb area of the human motor cortex.

In 18 neurologically normal subjects the corticofugal volleys evoked by anodal and cathodal electrical stimulation of the motor cortex were recorded using epidural electrodes at the high-thoracic and low-thoracic regions of the spinal cord during surgery for scoliosis. At and just above threshold, anodal and cathodal stimulation of the upper-limb area and motor cortex produced a D wave that propagated to the low-thoracic region. The stimulus intensity required to produce D waves was significantly lower with anodal stimulation. I waves were recorded at higher stimulus intensities than the D wave but not more readily with cathodal stimulation. There was no significant difference in the extent to which stimulus intensity had to be increased above D-wave threshold to produce I waves with the two stimulus polarities, and the number of I waves was the same when the stimulus was increased by the same amount above D-wave threshold. After withdrawal of isoflurane, I waves could not be recorded when the stimulus intensity was below D-wave threshold with either stimulus polarity. Anodal stimulation over the upper-limb area remained more effective than cathodal stimulation in producing both D and I waves. These results indicate that, at threshold, regardless of anaesthesia, anodal and cathodal stimuli access upper-limb corticospinal neurons directly at a similar site, the anodal stimuli being more effective. In addition, the results suggest that some corticospinal neurons in the upper-limb area of motor cortex have projections to lumbar segments.

Adolescent↗

PubMed1978

Does the supplementary motor area play a part in modifying motor cortex reflexes?

Neuronal activity in the supplementary motor area was recorded from a monkey performing a trained motor task that required readiness for proper usage of sensory inputs. Thirty-two neurons exhibited activity changes, which supports the hypothesis that the SMA is part of the system involved in modulating responsiveness of the motor cortex to sensory inputs in association with learned movements.

Animals↗

PubMed1992

Topographic mapping of the human motor cortex with magnetic stimulation: factors affecting accuracy and reproducibility.

We recorded motor evoked potentials (MEPs) from deltoid, biceps brachii, abductor pollicis brevis and flexor carpi radialis muscles of 5 normal volunteers during transcranial magnetic stimulation. With the subjects at rest, an 8-shaped magnetic coil was used to deliver 30 stimuli to different scalp positions 0.5 or 1.0 cm apart. The variability in amplitude and latency of MEPs was studied as a function of the scalp position stimulated, the number of stimuli at each position, and the percentage of maximal peripheral M responses (%M) elicited. The results were used to estimate the optimal number of stimuli at each position and the optimal spacing of scalp positions for topographic mapping of the human motor cortex. The amplitude and latency variability of MEPs were higher when suboptimal scalp positions were stimulated. Consequently, a larger number of stimuli were required to determine representative MEP amplitudes at suboptimal positions. In addition, there was an inverse relationship between %M recruited by transcranial magnetic stimuli in different subjects and the variability in MEP amplitude and latency. Latency variability was less pronounced than amplitude variability. Optimal sampling conditions are required to produce the best topographic maps, particularly to show subtle reorganization patterns in the human motor cortex.

Brain Mapping↗