Cerebral Motor Cortex Research Articles

Noxious Lingual Stimulation Influences the Excitability of the Face Primary Motor Cerebral Cortex (Face MI) in the Rat

The mechanisms whereby orofacial pain affects motor function are poorly understood. The aims were to determine whether 1) lingual algesic chemical stimulation affected face primary motor cerebral cortex (face MI) excitability defined by intracortical microstimulation (ICMS); and 2) any such effects were limited to the motor efferent MI zones driving muscles in the vicinity of the noxious stimulus. Ketamine-anesthetized Sprague-Dawley male rats were implanted with electromyographic (EMG) electrodes into anterior digastric, masseter, and genioglossus muscles. In 38 rats, three microelectrodes were located in left face MI at ICMS-defined sites for evoking digastric and/or genioglossus responses. ICMS thresholds for evoking EMG activity from each site were determined every 15 min for 1 h, then the right anterior tongue was infused (20 microl, 120 microl/h) with glutamate (1.0 M, n = 18) or isotonic saline (n = 7). Subsequently, ICMS thresholds were determined every 15 min for 4 h. In intact control rats (n = 13), ICMS thresholds were recorded over 5 h. Only left and right genioglossus ICMS thresholds were significantly increased (< or =350%) in the glutamate infusion group compared with intact and isotonic saline groups (P < 0.05). These dramatic effects of glutamate on ICMS-evoked genioglossus activity contrast with its weak effects only on right genioglossus activity evoked from the internal capsule or hypoglossal nucleus. This is the first documentation that intraoral noxious stimulation results in prolonged neuroplastic changes manifested as a decrease in face MI excitability. These changes appear to occur predominantly in those parts of face MI that provide motor output to the orofacial region receiving the noxious stimulation.

Impaired cortical activation in autistic children: Is the mirror neuron system involved?

The inability to imitate becomes obvious early in autistic children and seems to contribute to learning delay and to disorders of communication and contact. Posture, motility and imitation disorders in autistic syndrome might be the consequence of an abnormality of sensori-motor integration, related to the visual perception of movement, and could reflect impairment of the mirror neuron system (MNS). We compared EEG activity during the observation of videos showing actions or still scenes in 14 right-handed autistic children and 14 right-handed, age- and gender-matched control children (3 girls and 11 boys, aged 5 years 3 months–7 years 11 months). We showed desynchronisation of the EEG in the motor cerebral cortex and the frontal and temporal areas during observation of human actions in the group of healthy children. No such desynchronisation was found in autistic children. Moreover, inversion of the pattern of hemispheric activation was found in autistic children, with increased cortical activity in the right hemisphere in the posterior region, including the centro-parietal and temporo-occipital sites. These results are in agreement with the hypothesis of impairment of the mirror neuron system in autistic disorder.

Isolated Hand Palsy Due to Cortical Infarction: Localization of the Motor Hand Area

To evaluate the cortical presentation of the hand area according to MRI images of the infarcted area in patients who have predominantly hand weakness. "Pseudoperipheral palsy" is an old term employed to describe a rare clinical picture consisting of predominant weakness of the hand in association with cerebral infarction. Because the organization of the cortical efferent area of the hand has not been fully defined, this phenomenon merits attention. Recent advances in functional imaging have stimulated renewed interest in the cortical mapping of various body parts, particularly that of the hand. The patients who had isolated hand palsy due to cerebral infarction underwent clinical examination and cerebral MRI investigation to locate the exact lesion site. Eight patients (6 men, 2 women) aged 55 to 80 years (mean 69 years) were included in this study. All had at least one risk factor for cerebrovascular disease. All our 8 patients presented with hand palsy and lesions were detected in the contralateral precentral gyrus in all cases. The lesions were located in the middle to lower portion of the anterior wall of the central sulcus just posterior to the intersection of the superior frontal and precentral sulci. Our findings indicate that the hand area in the cerebral motor cortex is located in the middle to lower portion of the anterior wall of the central sulcus, that is, in Brodmann area 4. We present our 8 patients showing isolated hand palsy due to a discrete cortical infarction on MRI to expand the knowledge about cortical localization of the hand area.

Melanin-concentrating hormone projections to areas involved in somatomotor responses

The lateral hypothalamic area (LHA) participates in the integration of sensory information and somatomotor responses associated with hunger and thirst. Although the LHA is neurochemically heterogeneous, a particularly high number of cells express melanin-concentrating hormone (MCH), which has been reported to play a role in energy homeostasis. Treatment with MCH increases food intake, and MCH mRNA is overexpressed in leptin-deficient ( ob/ ob) mice. Mice lacking both MCH and leptin present reduced body fat, mainly due to increased resting energy expenditure and locomotor activity. Dense MCH innervation of the cerebral motor cortex (MCx) and the pedunculopontine tegmental nucleus (PPT), both related to motor function, has been reported. Therefore, we postulated that a specific group of MCH neurons project to these areas. To investigate our hypothesis, we injected retrograde tracers into the MCx and the PPT of rats, combined with immunohistochemistry. We found that 25% of the LHA neurons projecting to the PPT were immunoreactive for MCH, and that 75% of the LHA neurons projecting to the MCx also contained MCH. Few MCH neurons were found to send collaterals to both areas. We also found that 15% of the incerto-hypothalamic neurons projecting to the PPT expressed MCH immunoreactivity. Those neurons preferentially innervated the rostral PPT. In addition, we observed that the MCH neurons express glutamic acid decarboxylase mRNA, a gamma-aminobutyric acid (GABA) synthesizing enzyme. We postulate that MCH/GABA neurons are involved in the inhibitory modulation of the innervated areas, decreasing motor activity in states of negative energy balance.

Anticipatory changes in beta synchrony in the human corticospinal system and associated improvements in task performance

Synchronized oscillatory activity in the beta frequency band (13-30 Hz) can be detected in the cerebral motor cortex of healthy humans in the form of corticomuscular coherence. Elevated beta activity is associated with impaired processing of new movements and with more efficient postural or tonic contraction. Accordingly, beta activity is suppressed prior to voluntary movements, rebounding thereafter in the face of peripheral afferance. However, it remains to be established whether synchronized activity in the beta band can be up-regulated in a task-appropriate way independently of confounding changes in sensory afferance. Here we show that there is a systematic and prospective increase in beta synchrony prior to an expected postural challenge. This up-regulation of beta synchrony is associated with improved behavioural performance. We instructed nine healthy subjects to perform a reaction-time movement of the index finger in response to an imperative visual cue or to resist a stretch to the finger in the same direction. These events were preceded by congruent and less common incongruent warning cues. Beta synchrony was temporally increased when subjects were warned of an impending stretch and decreased following a warning cue signalling a forthcoming reaction-time task. Finger positions were less successfully maintained in the face of stretches and reaction times were longer when warning cues were incongruent. The results suggest that the beta state is modulated in a task-relevant way with accompanying behavioural consequences.

Role of cerebellum in learning postural tasks

For a long time, the cerebellum has been known to be a structure related to posture and equilibrium control. According to the anatomic structure of inputs and internal structure of the cerebellum, its role in learning was theoretically reasoned and experimentally proved. The hypothesis of an inverse internal model based on feedback-error learning mechanism combines feedforward control by the cerebellum and feedback control by the cerebral motor cortex. The cerebellar cortex is suggested to acquire internal models of the body and objects in the external world. During learning of a new tool the motor cortex receives feedback from the realized movement while the cerebellum produces only feedforward command. To realize a desired movement without feedback of the realized movement, the cerebellum needs to form an inverse model of the hand/arm system. This suggestion was supported by FMRi data. The role of cerebellum in learning new postural tasks mainly concerns reorganization of natural synergies. A learned postural pattern in dogs has been shown to be disturbed after lesions of the cerebral motor cortex or cerebellar nuclei. In humans, learning voluntary control of center of pressure position is greatly disturbed after cerebellar lesions. However, motor cortex and basal ganglia are also involved in the feedback learning postural tasks.

Improved outcome of facial nerve repair in rats is associated with enhanced regenerative response of motoneurons and augmented neocortical plasticity

Within a recent study on the vibrissae motor performance after facial nerve repair in strains of blind (SD/RCS) and sighted (SD) rats we found that, despite persisting myotopic disorganization in the facial nucleus, the blind animals fully restored vibrissal whisking. Here we searched for morphological substrates of better recovery in the regenerating motoneurons and in the cerebral motor cortex. Expression analyses of the neurite growth-related proteins f-actin, neuronal class III beta-tubulin and plasticity-related gene-1, and stereological estimates of growth cone densities revealed a more vigorous regenerative response in the proximal nerve stump of blind SD/RCS rats compared with SD animals at 5-7 days after buccal nerve transection. Using c-Fos immunoreactivity as a marker for neuronal activation, we found that the volume of the cortex acutely responding to nerve transection (facial muscles reactive volume, FMRV) in both hemispheres of intact sighted rats was twofold smaller than that measured in blind animals. One month after transection and suture of the right facial nerve (FFA) we found a twofold increase in the FMRV in both rat strains compared with intact animals. The FMRV in SD/RCS animals, but not in SD rats, returned to the values in intact rats 2 months after FFA. Our findings suggest that enhanced plasticity in the CNS and an augmented regenerative response of the injured motoneurons contribute to better functional recovery in blind rats.

Neuronal damage and changes in the expression of muscarinic acetylcholine receptor subtypes in the neonatal rat cerebral cortical upon exposure to sparteine, a quinolizidine alkaloid

Sparteine is a quinolizidine alkaloid (QA) produced by Lupine species that has generated much interest due to its anti-hypertensive, anti-pyretic, and anti-inflammatory properties. In the nervous system, sparteine has been shown to display anti-cholinergic and depressive activity, although how sparteine exerts its toxic effects in the brain remains unclear. We have addressed this issue by administering subcutaneous injections of sparteine (25mg/kg of body weight) to rats on postnatal days 1 and 3, and then examining the expression of the muscarinic acetylcholine receptor (mAChR) subunits m1–m4 in the brains of the neonatal rats 14–60 days later. Administration of sparteine to neonatal rats caused neuronal damage in the cerebral motor cortex accompanied by transient changes in the expression of m1–m4 mAChR subunits as revealed by both RT-PCR and Western blotting. This effect could be prevented by pre-treatment with atropine (10mg/kg) 1h prior to the injection of sparteine, suggesting that the cytotoxic activity of sparteine is mediated through mAChRs.

Somatomotor functional MRI in a hypertensive arachnoid cyst

In this article the authors report the study by functional MRI, before and after surgery, of the motor cerebral cortex surrounding a large hypertensive arachnoid cyst. They stress that the functional modifications due to surgery are more relevant than suggested by the simple morphological data.

Reliability of Cerebral and Muscle Oxygenation/Blood Volume During Hand-Gripping Measured Simultaneously by Near Infrared Spectroscopy

The stimulus to contract a muscle originates in the cerebral motor cortex and is transmitted to the motor unit via the spinal cord. Near infrared spectroscopy (NIRS) has been used to measure both cerebral and muscle oxygenation (Cox, Mox) /blood volume (Cbv, Mbv) changes during exercise. Although the reliability of these measurements has been reported separately in both tissues, their reproducibility in these two tissues has not been examined simultaneously. PURPOSE: To examine the reliability of the Cox/Mox/Cbv/Mbv measurements during handgrip exercise in healthy subjects. METHODS: Informed consent was obtained from six volunteers (mean age = 28 ± 13 yr, grip strength = 30.4 ± 10.8 kg) who completed two identical testing sessions 24h apart. After a 2min baseline, each subject performed maximal handgrip contractions on a dynamometer (Takei, Japan) with their dominant hand continuously for 15sec, and intermittently for 60sec at a contraction rate of 10/min without hyperventilation during the same session. A 2min rest was allowed between the two protocols. NIRS responses were recorded simultaneously from the extensor carpi ulnaris of the dominant forearm and the contralateral frontal lobe using a dual wavelength spectrometer (MicroRunman, NIM Inc., PA). Delta values were calculated as the difference between the resting value just before initiation of contraction and the maximal value observed during the test and/or recovery period. Values for the two protocols were pooled (N = 12) for statistical analysis. RESULTS: During trials 1 and 2, Mox and Mbv showed a consistent decrease (−0.306±0.069, −0.270±0.082, −0.300±0.086 and −0.315±0.054 respectively), whereas Cox and Cbv demonstrated a continual increase (0.069±0.027, 0.076±0.036, 0.076±0.036 and 0.033±0.015 respectively). The intraclass correlation coefficients for the Cox, Cbv, Mox and Mbv were 0.86 (p=0.001), 0.82 (p=0.004), 0.60 (p=0.085) and 0.32 (p=0.281) respectively. No significant differences were observed between the mean values of the two sessions for each of the variables (p=0.106, 0.372, 0.639, and 0.216 for Cox, Cbv, Mox, and Mbv). Bland-Altman analysis indicated no outliers for the cerebral measurements, whereas there was one outlier for the Mbv. The half recovery time for Mox (an index of muscle aerobic capacity) demonstrated moderate reliability (ICC = 0.72, p=0.023). CONCLUSIONS: The evidence indicates that: (1) the Cox, Cbv and Mox responses, as well as half recovery time for Mox, measured by NIRS are reproducible, and (2) the consistency of the measurements is higher in cerebral compared to muscle tissue. Funding: First author was supported by Ministério da Educação / CAPES, Brazil.

Supratentorial Low-Grade Glioma Resectability: Statistical Predictive Analysis Based on Anatomic MR Features and Tumor Characteristics

To retrospectively assess the main variables that affect the complete magnetic resonance (MR) imaging-guided resection of supratentorial low-grade gliomas. Institutional review board approval was obtained for this retrospective HIPAA-compliant study, with the requirement for informed consent waived. Data from 101 patients (61 men, 40 women; mean age, 39 years; age range, 18-72 years) who had nonenhancing supratentorial mass lesions that were histopathologically diagnosed as low-grade (World Health Organization grade II) gliomas and consecutively underwent surgery with intraoperative MR imaging guidance were analyzed. There were 21 low-grade astrocytomas, 64 oligodendrogliomas, and 16 mixed oligoastrocytomas. Initial and residual tumor volumes were measured on intraoperative T2-weighted MR images and three-dimensional spoiled gradient-echo MR images. The anatomic relationships between the tumor and eloquent cortical and/or subcortical regions and the influence of these relationships on the extent of resection were analyzed on the basis of preoperative MR imaging findings. Summary measures, univariate Fisher exact test and t test, and multivariate logistic regression analyses were performed. Tumor volume ranged from 2.7-231.0 mL. Univariate analyses revealed the following tumor characteristics to be significant predictive variables of incomplete tumor resection: diffuse tumor margin on T2-weighted MR images, oligodendroglioma or oligoastrocytoma histopathologic type, and large tumor volume (P < .05 for all). Tumor involvement of the following structures was associated with incomplete resection: corpus callosum, corticospinal tract, insular lobe, middle cerebral artery, motor cortex, optic radiation, visual cortex, and basal ganglia (P < .05 for all). Multivariate analyses revealed that incomplete tumor resection was due to tumor involvement of the corticospinal tract (P < .01), large tumor volume (P < .01), and oligodendroglioma histopathologic type (P = .02). The main variables associated with incomplete tumor resection in 101 patients were identified by using statistical predictive analyses.

Functional significance of the ipsilateral hemisphere during movement of the affected hand after stroke

Previous fMRI observations have suggested increased task-related activation of the ipsilateral cerebral motor cortex in patients recovering from stroke. This is generally taken to infer an increased output from this area, although the functional relevance of this has been questioned. Here, we use directed EEG coherence to reveal whether there is increased informational flow from the ipsilateral motor cortex following motor stroke, and through correlation with degree of recovery, establish that this pattern of activity is associated with limited functional improvement. Unrecovered (n = 14), recovered (n = 11) patients and healthy subjects (n = 16) performed an isometric grip task with either hand that corresponded to 25% of individual maximum force, while EEG was recorded. For unrecovered stroke patients, most task-related information flow between the sensorimotor cortices in the low beta band of the EEG came from the ipsilateral (undamaged) hemisphere during grip with the affected hand. This was not the case when they gripped with their unaffected hand, when cortical activity was driven from the contralateral sensorimotor cortex. The latter pattern was also seen in recovered patients and controls. These findings suggest a functional role for the ipsilateral hemisphere in organizing movement of the impaired limb following stroke, but only in those patients that do not make a good functional recovery. Patients making a fuller recovery organize movement-related cortical activity from the hemisphere contralateral to movement.

Treatment-induced neuroplasticity following focal injury to the motor cortex.

The impairment and functional limitation associated with damage to the cerebral motor cortex is often severely disabling and can lead to extensive rehabilitation. Unfortunately, much of this rehabilitation intervention lacks a solid foundation of empirically derived evidence of its efficacy. Moreover, the continuing knowledge explosion in healthcare necessitates the need to stay abreast of ever-changing developments in rehabilitation. This paper introduces the reader to introductory neuroplasticity concepts and outlines the current knowledge on neuroplastic changes in the motor cortex, which are driven by rehabilitation. Furthermore, this paper discusses neuroplasticity concepts that can serve as a theoretical foundation behind treatment intervention.

Subchronic Dermal Application of N,N-Diethyl m-Toluamide (DEET) and Permethrin to Adult Rats, Alone or in Combination, Causes Diffuse Neuronal Cell Death and Cytoskeletal Abnormalities in the Cerebral Cortex and the Hippocampus, and Purkinje Neuron Loss in the Cerebellum

N,N-Diethyl m-toluamide (DEET) and permethrin have been implicated as potential neurotoxic agents that may have played an important role in the development of illnesses in some veterans of the Persian Gulf War. To determine the effect of subchronic dermal application of these chemicals on the adult brain, we evaluated histopathological alterations in the brain of adult male rats following a daily dermal dose of DEET (40 mg/kg in 70% ethanol) or permethrin (0.13 mg/kg in 70% ethanol) or a combination of the two for 60 days. Control rats received a daily dermal dose of 70% ethanol for 60 days. Animals were perfused and brains were processed for morphological and histopathological analyses following the above regimen. Quantification of the density of healthy (or surviving) neurons in the motor cerebral cortex, the dentate gyrus, the CA1 and CA3 subfields of the hippocampus, and the cerebellum revealed significant reductions in all three treated groups compared with the control group. Further, animals receiving either DEET or permethrin exhibited a significant number of degenerating (eosinophilic) neurons in the above brain regions. However, degenerating neurons were infrequent in animals receiving both DEET and permethrin, suggesting that neuronal cell death occurs earlier in animals receiving combined DEET and permethrin than in animals receiving either DEET or permethrin alone. The extent of neuron loss in different brain regions was similar among the three treatment groups except the dentate gyrus, where neurodegeneration was significantly greater with exposure to DEET alone. The neuron loss in the motor cerebral cortex and the CA1 subfield of all treated groups was also corroborated by a significant decrease in microtubule associated protein 2-immunoreactive elements (15–52% reduction), with maximal reductions occurring in rats receiving DEET alone; further, the surviving neurons in animals receiving both DEET and permethrin exhibited wavy and beaded dendrites. Analysis of glial fibrillary acidic protein immunoreactivity revealed significant hypertrophy of astrocytes in the hippocampus and the cerebellum of all treated groups (24–106% increase). Thus, subchronic dermal application of DEET and permethrin to adult rats, alone or in combination, leads to a diffuse neuronal cell death in the cerebral cortex, the hippocampal formation, and the cerebellum. Collectively, the above alterations can lead to many physiological, pharmacological, and behavioral abnormalities, particularly motor deficits and learning and memory dysfunction.

Effects of sensory feedback on variations on intertap interval and force in finger-tapping sequences.

This study was designed to examine effects of somatosensory feedback on variations of intertap interval and muscle force in finger-tapping sequences over 10 minutes. Although intertap intervals were decreased on the massed task as the time passed, the intervals were constant in the distributed task. In finger-tapping for a long time, impulses perhaps circulate within the loop circuits between the cerebral motor cortex and the peripheral nerve and subsequently increase further the excitability of the circuits. This increase in the excitability within the circuits may shorten the interval and increase variation of the interval. On the other hand, although peak force increased up to the 5-min. mark on the massed task, the force decreased after the 6-min. mark. This increase of force also may be produced by increasing activation of the corticoperipheral loop circuits. Although the decrease of force was perhaps produced by the fatigue of finger muscles for tapping during a few minutes, fatigue appeared more clearly in muscle force than in timing control. However, the force and the variation were constant in the distributed task.

Cortical catecholamine changes and seizures induced by 4-aminopyridine in awake rats, studied with a dual microdialysis-electrical recording technique

We describe a rotatory electrical device that permits the simultaneous microdialysis and electroencephalographic (EEG) recording, by means of bipolar electrodes attached to the microdialysis probe, in two brain regions of awake rats. Using this device, we have found that the microdialysis infusion of 4-aminopyridine (4-AP) in the motor cerebral cortex produces intense behavioral convulsions and EEG seizures in both the infused and the contralateral cortex. This convulsant action is accompanied by a remarkable increase of extracellular dopamine (about 15-fold), norepinephrine (2.4-fold) and vanillylmandelic acid (1.8-fold) concentration in the infused cortex. Delayed increases of these amines were observed also in the contralateral cortex. The results suggest that 4-AP induces the release of catecholamines either through a direct effect on nerve endings or as a consequence of seizures.

Potentiels évoqués moteurs obtenus par stimulation corticale en double choc: techniques et interprétations

The technique of motor evoked potentials (MEP) obtained with single and double magnetic stimulation of the motor cortex in man has considerably improved over the past decade. We present the techniques and parameters involved in double magnetic stimulation for clinical purposes. The conditioning-test design is used to study modifications in the amplitudes of the muscular responses to the "test" shock, recorded on the first dorsal interosseus muscle. Enhanced amplitudes of conditioned responses indicate facilitation, reduced response inhibition. The effects vary according to the shock intensity, the delay between shocks and the position of the conditioning coil. The latter may be located at the same place as the test shock (to test interneural circuitry related to pyramidal tract), on the hand area opposite the test shock (to test interhemispheric influences), or over the cerebellar area contralateral to the test side (to test the effect of cerebellar stimulations over the motor cortex). When the coils were located on the same cortical hand area there was facilitation when the intensities were both set at the threshold with an interstimulus interval (ISI) between 1 and 2.5-3 ms. At conditioning shock intensities below the threshold and the test shock 150% above, inhibition occurred at ISI 1-5 ms followed by facilitation at ISI 15-35 ms. When the intensities of both shocks were 150% above threshold, there were two clear cut individual responses at ISI above 10 ms; facilitation was recorded at ISI 15-35 ms, and inhibition between 55 and 255 ms. When the conditioning coil was located on the opposite hand area from the test shock (conditioning shock intensity supramaximal, test shock intensity above the threshold), ISI 1-5 ms facilitation occurred followed by inhibition up to ISI 30 ms. When the conditioning shock (intensity supramaximal) was located on the cerebellar area contralateral to the test side (intensity above the threshold), inhibition occurred at ISI 5 ms. Double magnetic stimulations delivered over the same cortical area reflect facilitatory and inhibitory influences over the pyramidal tract controlled by interneurons, i.e., these tests investigate the intrinsic circuitry of the motor strip. Double magnetic stimulations delivered on each motor area study interhemispheric influences mediated by the corpus callosum, which are facilitatory and inhibitory. Double magnetic stimulations delivered on the cerebellar area demonstrates inhibitory influences over the contralateral cerebral motor cortex.

Effects of voluntary contraction on descending volleys evoked by transcranial electrical stimulation over the motor cortex hand area in conscious humans.

The spinal volleys evoked by electric anodal and cathodal stimulation over the cerebral motor cortex hand area were recorded from a bipolar electrode inserted into the cervical epidural space of two conscious human subjects. We measured the size of volleys elicited by electric stimulation at active motor threshold and at 3% of maximum stimulator output above this value with subjects at rest and during maximum voluntary contraction of the contralateral first dorsal interosseous muscle. Surface EMG activity was recorded at the same time. Electrical anodal stimulation evoked a single negative wave that we termed D-wave in analogy with data in experimental animals. Cathodal stimulation evoked a single negative wave with a latency of 0.2 ms longer than the D-wave recruited by anodal stimulation. At both intensities tested, voluntary contraction did not modify the amplitude of the descending waves. We conclude that changes in cortical excitability induced by voluntary activity do not modify the corticospinal volley evoked by electric stimulation and that the D-waves evoked by both anodal and cathodal electric stimulation are probably initiated several nodes distant to the cell body.

Functional MR Imaging in the Patients with Complex Partial Seizures

Purpose: To evaluate the clinical usefulness of functional MR imaging (fMRI) for localization of the cerebral motor and sensory cortices and the language center in patients with complex partial seizure. Materials and Methods: A total of 47 fMRIs were obtained in 14 patients (M:F=9:5; age 15 -50 years; 13 right handed and 1 ambidextrous) with complex partial seizure (6 temporal lobe epilepsy, 6 frontal lobe epilepsy, 1 occipitotemporal lobe epilepsy, 1 hemispheric epilepsy). Conventional MR imaging revealed no abnormality in four patients, localized cerebral atrophy in one, hippocampal sclerosis in four, and benign neoplasm in the remaining five. fMRI was performed on a 1.5 T MR scanner (GE Signa Horizon) using gradient-echo single-shot EPI. Nineteen fMRIs were obtained in eight patients who performed the language task, 16 fMRIs in ten who performed the motor task and 12 fMRIs in ten who performed the somatosensory task. The activation task consisted of three language tasks (silent picture naming, word generation from a character, categorical word generation), motor tasks (opposition of thumb and index finger for hand/dorsiflexion or extension for foot), and sensory tasks (passive tactile stimulation of hand or foot using a toothbrush). The data were analyzed using z-score (p

Comparison of descending volleys evoked by transcranial magnetic and electric stimulation in conscious humans

Objectives: The present experiments were designed to compare the understanding of the transcranial electric and magnetic stimulation of the human motorcortex. Methods: The spinal volleys evoked by single transcranial magnetic or electric stimulation over the cerebral motor cortex were recorded from a bipolar electrode inserted into the cervical epidural space of two conscious human subjects. These volleys were termed D- and I waves, according to their latency. Magnetic stimulation was performed with a figure-of-eight coil held over the right motor cortex at the optimum scalp position, in order to elicit motor responses in the contralateral FDI using two different orientations over the motor strip. The induced current flowed either in a postero-anterior or in a latero-medial direction. Results: At active motor threshold intensity, the electric anodal stimulation evoked pure D activity. At this intensity, magnetic stimulation with the induced current flowing in a posterior-anterior direction evoked pure I 1 activity. When a latero-medial induced current was used, magnetic stimulation evoked both D and I 1 activity. Using electric anodal stimulation, at a stimulus intensity of 9% of the stimulator output above the active motor threshold (corresponding approximately to 1.5 active motor threshold), a small I 1 wave appeared only in subject 1. Using magnetic stimulation with a posterior-anterior induced current, at a stimulus intensity of 21% of maximum stimulator output above the active motor threshold (corresponding approximately to 1.8 times threshold in subject 1 and to two times threshold in subject 2), a small D wave appeared in subject 1 but not in subject 2. Conclusions: Present results demonstrate that, in conscious humans at threshold intensities, electric stimulation evokes D waves and magnetic stimulation (with a posterior-anterior induced current) evokes I waves, while magnetic stimulation (with a latero-medial induced current) evokes both activities.