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At least 37 records · Page 2Linked to original sources
PubMed1995

Functional magnetic resonance imaging at 1 T: motor cortex, supplementary motor area and visual cortex activation.

Functional activation of the brain has been visualized using magnetic resonance imaging (MRI). Early studies used echo planar imaging and magnetic fields of 2 T and above. However, recent studies have successfully shown the activation of visual and motor areas of the brain using conventional clinical 1.5 T MRI systems. The purpose of the present study was to replicate these studies at a lower field strength. Eight motor and two visual activation studies were performed using a 1 T clinical scanner. Activation was seen in the contralateral motor cortex during motor stimulation in six of the eight volunteers. Activation was also documented within the contralateral supplementary motor area in four of the six volunteers with motor cortex activation. The supplementary motor area was located in the posteromedial aspect of the superior frontal gyrus. Both volunteers subjected to photic stimulation showed activation within the visual cortex. Results show that functional imaging can be successfully carried out with a 1 T clinical scanner. The size of the image intensity on activation change suggests that contrast may not be due solely to susceptibility changes.

Brain Mapping↗
PubMedDate not supplied

[Anticipatory postural adjustment in bimanual unloading: role of the motor cortex in motor learning].

The role of the motor cortex was investigated during learning unusual postural adjustment. Healthy subjects held their right (postural) forearm in a horizontal position while supporting a 1-kG load via an electromagnet. The postural forearm position was perturbed by the load release triggered by other elbow voluntary movement. Repetition of the imposed unloading test resulted in a progressive reduction of the maximal forearm rotation, accompanied by the anticipatory decrease in m. biceps brachii activity (learning). Control situation consisted of the voluntary forearm loading. Using the transcranial magnetic stimulation we examined changes in the motor evoked potential of the m. biceps brahii at the beginning and at the end of learning. The evoked potential amplitude did not significantly change in process of the decrease of m. biceps brachii activity. At the end of learning, motor evoked potential / baseline electromyogram ratio increased as compared to the beginning of learning and to the control situation. The results highlight the fundamental role of the motor cortex in suppression of synergies which interfere with formation of a new coordination during motor learning.

Adult↗
PubMed2006

Large-scale organization of preferred directions in the motor cortex. I. Motor cortical hyperacuity for forward reaching.

We used statistical methods for spherical density estimation to evaluate the distribution of preferred directions of motor cortical cells recorded from monkeys making reaching movements in 3D space. We found that this distribution, although broad enough to represent the entire 3D continuum of reaching directions, exhibited an enrichment for reaching forward from the body and, to a lesser degree, for reaching backward toward the body. The distribution of preferred directions of cells in the motor cortex may have important implications for motor cortical function and for the decoding of arm trajectories from population activity.

Algorithms↗
PubMed1993

Transcranial electric and magnetic stimulation of the leg area of the human motor cortex: single motor unit and surface EMG responses in the tibialis anterior muscle.

We compared single motor unit and surface EMG responses in the active right tibialis anterior following anodal electrical or magnetic stimulation of the motor cortex over the vertex. Magnetic stimulation used a monophasic current pulse through a circular coil centred 3 cm anterior to the vertex. Lowest threshold magnetic stimulation occurred when the current in the coil flowed from the left to the right side at the posterior rim of the coil. Such stimulation produced single unit and surface EMG responses which had the same latency as those produced by anodal electric stimulation. If the direction of the magnetic stimulating current was reversed, response latencies became more variable from unit to unit, and on average they occurred 1.0 +/- 0.5 msec later. In single motor units anodal and magnetic post-stimulus time histogram (PSTH) peaks had the same duration. This was similar to the duration of the PSTH peaks produced by a single low intensity stimulus given to the common peroneal nerve. We conclude that magnetic stimulation can produce direct activation of corticospinal neurones to the tibialis anterior if the direction of induced current flow is optimal. This projection is likely to be either monosynaptic or oligosynaptic.

Adult↗
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↗
PubMed2000

Ipsilateral involvement of primary motor cortex during motor imagery.

To investigate whether motor imagery involves ipsilateral cortical regions, we studied haemodynamic changes in portions of the motor cortex of 14 right-handed volunteers during actual motor performance (MP) and kinesthetic motor imagery (MI) of simple sequences of unilateral left or right finger movements, using functional magnetic resonance imaging (fMRI). Increases in mean normalized fMRI signal intensities over values obtained during the control (visual imagery) task were found during both MP and MI in the posterior part of the precentral gyrus and supplementary motor area, both on the contralateral and ipsilateral hemispheres. In the left lateral premotor cortex, fMRI signals were increased during imagery of either left or right finger movements. Ipsilateral cortical clusters displaying fMRI signal changes during both MP and MI were identified by correlation analyses in 10 out of 14 subjects; their extent was larger in the left hemisphere. A larger cortical population involved during both contralateral MP and MI was found in all subjects. The overall spatial extent of both the contralateral and the ipsilateral MP + MI clusters was approximately 90% of the whole cortical volume activated during MP. These results suggest that overlapping neural networks in motor and premotor cortex of the contralateral and ipsilateral hemispheres are involved during imagery and execution of simple motor tasks.

Adult↗
PubMed1998

[Surgical management for preserving motor function in patients with gliomas near the primary motor cortex: usefulness of preoperative identification of motor cortex and intraoperative monitoring of motor evoked potentials].

Preoperative identification of precentral gyrus and intraoperative monitoring of motor evoked potentials (MEPs) were performed to preserve postoperative motor function in seven patients with gliomas near the primary motor cortex. Tumors were astrocytomas in 3 patients, glioblastomas in 2 patients, anaplastic astrocytoma and mixed glioma in one patient each. Preoperative identification of the primary motor cortex was performed by three-dimensional (3D) display of magnetic resonance (MR) images and by functional images using MR imaging and single-photon emission tomography. The primary motor cortex identified by 3D display of MR images coincided well with that identified by functional images. 3D display of MR images was also useful for detecting the relationship between the tumor and the primary motor cortex. Intraoperatively, the central sulcus was confirmed by the finding of phase reversal of cortical somatosensory evoked potential, and this corresponded with the preoperative identifications by 3D display and by functional mapping. The primary motor cortex was stimulated electrically, and MEP (corticospinal evoked potential) was continuously monitored during surgery using electrodes inserted in the cervical epidural space. The amplitude of direct waves of MEPs during surgery was maintained above half of that recorded at the beginning of tumor removal, and all patients showed preservation of preoperative motor function. These results suggest that preoperative identification of precentral gyrus and intraoperative MEP monitoring provide useful information for preserving motor function in patients with gliomas near the primary motor cortex.

Adult↗
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↗
PubMedDate not supplied

Effects of a rostral motor cortex lesion on primary motor cortex hand representation topography in primates.

BACKGROUND: Small lesions to rostral versus caudal portions of the hand representation in the primary motor cortex (M1) produce different behavioral deficits. The goal of the present study was to determine if rehabilitative training has similar effects on functional topography of the spared M1 after rostral versus previously reported caudal M1 lesions. METHODS: Following a lesion to the rostral M1 hand area, monkeys were trained for 1 h/day for 30 days to retrieve food pellets from small wells using their impaired hand. Electrophysiological maps of the M1 were derived in anesthetized monkeys before infarct and after rehabilitative training using intracortical microstimulation. RESULTS: After a lesion to the rostral M1 and rehabilitative training, the size of the spared hand representation decreased 1.2%. This change is not statistically different from the 9% increase seen after caudal M1 lesion and rehabilitative training (P > 0.2). CONCLUSION: Postlesion training spares peri-infarct hand area regardless of whether the lesion is in the rostral or caudal M1.

Animals↗
PubMed2005

Monosynaptic pathway from rat vibrissa motor cortex to facial motor neurons revealed by lentivirus-based axonal tracing.

The mammalian motor cortex typically innervates motor neurons indirectly via oligosynaptic pathways. However, evolution of skilled digit movements in humans, apes, and some monkey species is associated with the emergence of abundant monosynaptic cortical projections onto spinal motor neurons innervating distal limb muscles. Rats perform skilled movements with their whiskers, and we examined the possibility that the rat vibrissa motor cortex (VMC) projects monosynaptically onto facial motor neurons controlling the whisker movements. First, single injections of lentiviruses to VMC sites identified by intracortical microstimulations were used to label a distinct subpopulation of VMC axons or presynaptic terminals by expression of enhanced green fluorescent protein (GFP) or GFP-tagged synaptophysin, respectively. Four weeks after the injections, GFP and synaptophysin-GFP labeling of axons and putative presynaptic terminals was detected in the lateral portion of the facial nucleus (FN), in close proximity to motor neurons identified morphologically and by axonal back-labeling from the whisker follicles. The VMC projections were detected bilaterally, with threefold larger density of labeling in the contralateral FN. Next, multiple VMC injections were used to label a large portion of VMC axons, resulting in overall denser but still laterally restricted FN labeling. Ultrastructural analysis of the GFP-labeled VMC axons confirmed the existence of synaptic contacts onto dendrites and somata of FN motor neurons. These findings provide anatomical demonstration of monosynaptic VMC-to-FN pathway in the rat and show that lentivirus-based expression of GFP and GFP-tagged presynaptic proteins can be used as a high-resolution neuroanatomical tracing method.

Animals↗
PubMed2005

Rapid plastic changes of human primary motor cortex with repetitive motor practice and transcranial magnetic stimulation.

Excitability changes of human primary motor cortex are assumed to be associated with motor learning processes. To examine motor behavioral and neural mechanisms in these processes, the adaptive motor learning processes of the index finger abduction were investigated using motor evoked potential (MEP) elicited from the first dorsal interosseous and extensor carpi radialis muscles. Practice effects were examined on changes of MEP amplitudes elicited from these muscles during motor imagery. Given general consensus that the MEP amplitude change during motor imagery is a useful parameter reflecting changes in excitability of the human primary motor cortex, the present results, that MEP amplitudes of both muscles increased with repeated practice by the index finger abduction and that magnitudes of MEP amplitudes of both muscles (motor learning curves) were clearly different, suggested that participation of the muscles performing the index finger abduction gradually changed with practice. Short-term plastic changes of human primary motor cortex occur with repetitive practice and such adaptive change in human primary motor cortex is expressed in human voluntary movement that becomes more automatic.

Adult↗
PubMed2002

Focal enhancement of motor cortex excitability during motor imagery: a transcranial magnetic stimulation study.

OBJECTIVES: In order to learn more about the physiology of the motor cortex during motor imagery, we evaluated the changes in excitability of two different hand muscle representations in the primary motor cortex (M1) of both hemispheres during two imagery conditions. MATERIALS AND METHODS: We applied focal transcranial magnetic stimulation (TMS) over each M1, recording motor evoked potentials (MEPs) from the contralateral abductor pollicis brevis (APB) and first dorsal interosseus (FDI) muscles during rest, imagery of contralateral thumb abduction (C-APB), and imagery of ipsilateral thumb abduction (I-APB). We obtained measures of motor threshold (MT), MEP recruitment curve (MEP-rc) and F waves. RESULTS: Motor imagery compared with rest significantly decreased the MT and increased MEPs amplitude at stimulation intensities clearly above MT in condition C-APB, but not in condition I-APB. These effects were not significantly different between right and left hemisphere. MEPs simultaneously recorded from the FDI, which was not involved in the task, did not show facilitatory effects. There were no significant changes in F wave amplitude during motor imagery compared with rest. CONCLUSIONS: Imagery of unilateral simple movements is associated with increased excitability only of a highly specific representation in the contralateral M1 and does not differ between hemispheres.

Adult↗
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↗
PubMed2000

Intra-operative mapping of the motor cortex during surgery in and around the motor cortex.

The intra-operative use of neurophysiological techniques allows reliable identification of the sensorimotor region, and constitutes a prerequisite for its anatomical and functional preservation. The present prospective study combines monopolar cortical stimulation (MCS) with the recording of phase reversal of somatosensory evoked potentials (SEP-PR) in a protocol for the intra-operative mapping of the motor cortex. Functional mapping of the motor cortex by SEP-PR and MCS was performed in 70 patients during surgery in and around the motor cortex. The central sulcus was identified by SEP-PR. Cortical motor mapping was then performed by monopolar anodal (400 Hz) stimulation. Motor responses were recorded by needle electrodes placed in the muscles of the contralateral extremities. Surgery was performed under general anaesthesia without muscle relaxants. Intra-operative localization of the central sulcus by SEP-PR was possible in 68 patients (97.14%). Motor evoked potentials (MEP) were elicited following MCS in 67 cases (95.7%). In 3 cases no MEP was recorded, not even after maximal stimulation intensity, the central sulcus being localized by SEP-PR only. On the other hand, MCS allowed localizing the motor cortex in the 2 cases with no recordable SEP-PR. Thus, combining SEP-PR and MCS allowed intra-operative localization of the sensorimotor cortex in 100% of the cases.

Adolescent↗
PubMed2003

The ipsilateral human motor cortex can functionally compensate for acute contralateral motor cortex dysfunction.

What promotes motor recovery from stroke? To date, studies of recovery from stroke have shown alterations in function in various cortical areas, including the contralesional (unaffected) motor cortex (M1). However, whether these changes contribute to recovery or are mere epiphenomena remains unclear. We therefore sought evidence that the ipsilateral M1 can compensate for dysfunction of the contralateral M1. We recorded the change in force production during a finger-tapping task in response to acute disruption of M1 function by repetitive transcranial magnetic stimulation (rTMS). Neither control (occipital) nor ipsilateral M1 rTMS lead to a change in tapping force. RTMS over contralateral M1 had a short-lived effect and induced changes in ipsilateral M1 excitability around the time that these behavioral effects abated, consistent with delayed compensation by the ipsilateral M1. Simultaneous bilateral M1 stimulation, designed to prevent compensation by the ipsilateral M1, had a large and prolonged effect on tapping force. This is the first demonstration that the ipsilateral primary motor cortex is capable of functionally significant compensation for focal contralateral cortical dysfunction in the adult human and provides a rational basis for interventional treatments aimed at promoting functional compensation in unaffected cortical areas after stroke.

Biomechanical Phenomena↗
PubMed2003

Motor cortex stimulation enhances motor recovery and reduces peri-infarct dysfunction following ischemic insult.

Recovery of motor function following stroke is believed to be supported, at least in part, by functional compensation involving residual neural tissue. The present study used a rodent model of focal ischemia and intracortical microstimulation (ICMS) to examine the behavioral and physiological effects of cortical stimulation in combination with motor rehabilitation. Adult rats were trained to criterion on a single pellet reaching task before ICMS was used to derive maps of movement representations within forelimb motor cortex contralateral to the trained paw. All animals then received a focal ischemic infarct within the motor map. A cortical surface electrode was implanted over the motor cortex. Low levels of electrical stimulation were applied during rehabilitative training on the same reaching task for 10 days and ICMS used to derive a second motor map. Results showed that both monopolar and bipolar cortical stimulation significantly enhanced motor recovery and increased the area of cortex from which microstimulation movements could be evoked. The results demonstrate the behavioral and neurophysiological benefits of cortical stimulation in combination with rehabilitation for recovery from stroke.

Analysis of Variance↗
PubMed2001

Hemispheric asymmetry of ipsilateral motor cortex activation during unimanual motor tasks: further evidence for motor dominance.

OBJECTIVES: To test to which extent the increase in ipsilateral motor cortex excitability during unimanual motor tasks shows hemispheric asymmetry. METHODS: Six right-handed healthy subjects performed one of several motor tasks of different complexity (including rest) with one hand (task hand) while the other hand (non-task hand) was relaxed. Focal transcranial magnetic stimulation was applied to the motor cortex ipsilateral to the task hand and the amplitude of the motor evoked potential (MEP) in the non-task hand was measured. In one session, the task hand was the right hand, in the other session it was the left hand. The effects of motor task and side of the task hand were analyzed. Spinal motoneuron excitability was assessed using F-wave measurements. RESULTS: Motor tasks, in particular complex finger sequences, resulted in an increase in MEP amplitude in the non-task hand. This increase was significantly less when the right hand rather than the left hand was the task hand. This difference was seen only in muscles homologous to primary task muscles. The asymmetry could not be explained by changes in F-wave amplitudes. CONCLUSIONS: Hemispheric asymmetry of ipsilateral motor cortex activation either supports the idea that, in right handers, the left motor cortex is more active in ipsilateral hand movements, or alternatively, that the left motor cortex exerts more effective inhibitory control over the right motor cortex than vice versa. We suggest that hemispheric asymmetry of ipsilateral motor cortex activation is one property of motor dominance of the left motor cortex.

Adult↗
PubMed2002

Functional differences in corticospinal projections from macaque primary motor cortex and supplementary motor area.

We made a quantitative comparison of the density of macaque corticospinal projections from primary motor cortex (M1) and supplementary motor area (SMA) to spinal motor nuclei supplying hand and finger muscles. We also compared the action of corticospinal outputs from these two areas on 84 upper limb (mostly hand) motoneurones in chloralose-anaesthetised macaques. The hand representations of M1 and SMA were first identified using MRI and intracortical microstimulation. We made focal injections of WGA-HRP into these representations. Densitometric analysis showed that corticospinal projections from M1 were far denser and occupied a much greater proportion of the hand muscle motor nuclei than did SMA projections. Stimulation of M1 and SMA with bipolar intracortical pulses evoked monosynaptic EPSPs. These were significantly larger and more common from M1 (88% of motoneurons) than from SMA (48%). The results demonstrate corticomotoneuronal connections from both M1 and SMA, some converging upon single motoneurons. Both areas give rise to CM projections but that those from M1 are far more numerous and exert stronger excitatory effects than those from the SMA.

Animals↗