Desynchronization of cortical rhythms following cutaneous stimulation: effects of stimulus repetition and intensity, and of the size of corpus callosum.

OBJECTIVE: Event-related desynchronization (ERD) and synchronization (ERS) of the Rolandic electroencephalographic (EEG) rhythms following brief, innocuous electrocutaneous stimulation were studied with respect to stimulus intensity and repetition and the size of corpus callosum (CC). METHODS: EEG was recorded using 82 closely spaced electrodes in 13 right-handed subjects. The subjects received 650 brief electrical stimuli to the right index finger at irregular intervals (6-12 s) in 5 blocks. The intensities of the stimuli varied randomly at 20, 30, 50, 65 and 80% of pain threshold. RESULTS: Mu- and beta-ERD of 0.3-0.6 s latency over the contra- and ipsilateral S1/M1 area was observed in all subjects. Post-stimulus beta-ERS over the contra- and ipsilateral frontal cortices with a peak latency of 0.6-0.8 s was found in 9 subjects. Stimuli presented in the second half of the experiment were followed by a smaller ipsilateral mu-ERD and smaller contra- and ipsilateral beta-ERD than stimuli applied in the first block. Mu- and beta-ERD and beta-ERS distinguished weak (20%) from intermediate and strong stimuli (>35%) but not the intermediate from strong stimuli. The amplitude of ipsilateral beta-ERS correlated positively with the size of intermediate truncus of CC (r(9)=0.71, P<0.05). In contrast, ipsilateral ERD showed no significant correlations with the size of CC. CONCLUSIONS: Habituation of ipsilateral mu-ERD and bilateral beta-ERD and beta-ERS suggests that these cortical responses are parts of the orienting response, and fail to disentangle fine intensity gradations. Ipsilateral beta-ERS appears to be mediated by the transcallosal fiber system.     

Lateralization of movement-related potentials and the size of corpus callosum

Using structural MRI and whole-head EEG recordings, we analyzed the correlations between the anatomical parameters of the corpus callosum and the hemispheric distribution of the cortical movement-related potentials during right finger and shoulder movements in nine right-handed men. Statistically significant correlation was found only in finger movements. A relatively large genu and the anterior part of the truncus of the corpus callosum correlated with enhanced pre-movement EEG potential over the ipsilateral M1/S1 area. The lateralization of the movement-related potentials correlates with the size of those callosal regions which connect the homologous areas of the primary sensorimotor and frontal cortices.     

Movement-related electroencephalographic desynchronization in patients with hand cramps: evidence for motor cortical involvement in focal dystonia

We studied the dynamic changes in the amplitude of scalp electroencephalographic (EEG) oscillations to self-paced simple index finger abduction movements in patients with writer's cramp and compared them with those of normal aged-matched controls. The changes in EEG oscillations were measured in predefined frequency bands (8-10, 10-12, 12-20, and 20-30 Hz) by using the event-related desynchronization technique. Movements of the affected and unaffected hand in patients with writer's cramp showed significantly less reduction in 20- to 30-Hz power compared with controls. The differences in movement-related EEG power decline were apparent over the contralateral central and midline regions before and after electromyographic onset. Because EEG beta rhythm in the sensorimotor region likely emanates from the motor cortex and is related to ongoing muscle activity, this abnormality could be a manifestation of the abnormal motor command at the cortical level.     

Movement-related cortical potentials in writer's cramp

Movement-related cortical potentials in response to simple, self-paced, brisk index finger abduction movements were recorded in patients with simple and complex writer's cramp and compared with those of age-matched control subjects. Analysis of the movement-related cortical potential waveforms showed that the Bereitschaftspotential, the peak of the negative slope, and the frontal peak of the motor potential did not differ in the two groups, except for the average amplitude of the early part of the negative-slope peak, which was decreased in the patient group during the interval of 300 to 200 msec prior to electromyographic onset. This finding was restricted to the electrodes overlying the contralateral and midline central electrodes. Movement-related cortical potentials from patients and control subjects could be equally accounted for by a four-dipole source model with sources located in the contralateral and ipsilateral sensorimotor regions and the supplementary motor area. There was a trend for a reduction in the strength of the sensorimotor sources active during the premotor period in the patient group, but the difference did not reach a significant level for any individual source. No differences were found between the movement-related cortical potentials elicited by movements of the affected and unaffected hand, or between those of patients with simple or complex hand cramps. This result suggests a deficiency of contralateral motor cortex activation just prior to the initiation of voluntary movements in patients with focal dystonia.     

Different patterns of movement-related cortical oscillations in patients with myoclonus and in patients with spinocerebellar ataxia

ObjectiveTo assess whether different patterns of EEG rhythms during a Go/No-go motor task characterize patients with cortical myoclonus (EPM1) or with spinocerebellar ataxia (SCA).MethodsWe analyzed event-related desynchronization (ERD) and synchronization (ERS) in the alpha and beta-bands during visually cued Go/No-go task in 22 patients (11 with EPM1, 11 with SCA) and 11 controls.ResultsIn the Go condition, the only significant difference was a reduced contralateral beta-ERS in the EPM1 patients compared with controls; in the No-go condition, the EPM1 patients showed prolonged alpha-ERD in comparison with both controls and SCA patients, and reduced or delayed alpha- and beta-ERS in comparison with controls. In both conditions, the SCA patients, unlike EPM1 patients and controls, showed minimal or absent lateralization of alpha- and beta-ERD.ConclusionsEPM1 patients showed abnormal ERD/ERS dynamics, whereas SCA patients mainly showed defective ERD lateralization.SignificanceA different behavior of ERS/ERD distinguished the two patient groups: the pattern observed in EPM1 suggests a prominent defect of inhibition occurring in motor cortex contralateral to activated segment, whereas the pattern observed in SCA suggested a defective lateralization attributable to the damage of cerebello-cortical network, which is instead marginal in patients with cortical myoclonus.     

Movement-related cortical potentials in patients with Machado-Joseph disease.

ObjectiveMovement-related cortical potentials (MRCP; nomenclature of MRCP components according to Shibasaki and Hallett (Shibasaki H, Hallett M. What is the Bereitschaftspotential? Clin Neurophysiol 2006;117:2341–56) were studied in patients with Machado–Joseph disease (MJD) to elucidate the pathophysiology of voluntary movement.MethodsWe studied nine genetically proven MJD patients and eight age-matched healthy subjects. Multi-channel electroencephalogram (EEG) recordings were obtained during self-paced fast extensions of the wrist. EEG epochs were time-locked to electromyography (EMG) onset or offset of the voluntary EMG burst and averaged.ResultsIn the MJD patients, the early Bereitschaftspotential (early BP, −1500 to −500 ms) was not affected but the late BP was reduced over the central midline area and contralaterally to the movement side. The amplitude of the fpMP, a post-movement MRCP component, was also reduced. In addition, the offset cortical potential in the first 500 ms after EMG offset (Moff + 500) was attenuated bilaterally over a wide cortical area.ConclusionsFindings suggest that cortical activations associated with the initiation and termination of a voluntary movement are impaired in MJD patients.SignificanceAbnormalities of pre- and post-movement MRCP components provide researchers with pathophysiological insight into voluntary motor dysfunction in MJD.     

Task-related coherence and task-related spectral power changes during sequential finger movements

In order to investigate the activity of cortical regions in the control of complex movements, we studied task-related coherence (TRCoh) and task-related spectral power (TRPow) changes in 8 right-handed subjects during the execution of 4 different finger movement sequences of increasing complexity. All sequences were performed with the right hand and were paced by a metronome at 2 Hz. EEG power spectra and coherence values were computed within alpha (8-12 Hz) and beta (13-20 Hz) frequency bands for 29 scalp EEG positions during the execution of the sequences and were compared with values obtained during a rest (control) condition. Movement sequences were associated with TRPow decreases in the alpha and beta frequency bands over bilateral sensorimotor and parietal areas, with a preponderance over the contralateral hemisphere. Increases of TRCoh occurred over bilateral frontocentral regions. TRCoh decreases were present over the temporal and occipital areas. The spatial extent and the magnitude of TRPow decreases and TRCoh increases in both frequency bands were greater for sequential movements of higher complexity than for simpler ones. These results are consistent with previous findings of bilateral activation of sensorimotor areas during sequential finger movements. Moreover, the present results indicate an active intercommunication between bilateral and mesial central and prefrontal regions which becomes more intense with more complex sequential movements.     

Post-movement beta synchronization. A correlate of an idling motor area?

Post-movement beta (around 20 Hz) synchronization was investigated in 2 experiments with self-paced finger extension and flexion and externally paced wrist movement. The electrodes were fixed over the sensorimotor area in distances of 2.5 cm. It was found that after a brisk finger movement the desynchronized beta rhythm displayed a fast recovery and a short-lasting synchronization within 1 sec. This post-movement beta synchronization was maximal over the contralateral hemisphere and localized slightly more anterior to the maximal desynchronization of the hand area mu rhythm. The post-movement beta synchronization is interpreted as a correlate of “idling” motor cortex neurons.     

Non-linear EEG dynamic changes and their probable relation to voluntary movement organization.

This study was undertaken to analyze systematically the non-linear dynamic changes of EEG activity accompanying slow goal-directed voluntary movements, using three non-linear characteristics (NC): point-wise correlation dimension, Kolmogorov entropy and largest Lyapunov exponents as functions of time. NC indicated transitions with non-linear properties (NT). A significant difference between times of appearance of the NT with respect to the electrode position was established: before the movement onset, NT appeared first in contralateral and midline areas including frontal, sensorimotor and parietal cortices. Before target reaching, NT appeared first in the contralateral sensorimotor area, and evolved ipsilaterally. The results suggest that the NT could be regarded as precursors of higher functional coupling between cortical areas involved in voluntary movement organization.     

Cortical potentials preceding voluntary movement: evidence for three periods of preparation in man

We have recorded movement-related cortical potentials (MRCPs) to voluntary middle finger extension from 10 young and 10 old subjects free of neurological disease using the method of detecting EMG onset associated with each movement described by Barrett et al. (1985). The slow potential shifts preceding movement were measured by fitting a linear regression line to the wave forms to obtain a measure of their slope. Three separate potential shifts were identified. The first had a scalp distribution and onset latency similar to the Bereitschaftspotential (BP) first reported by Kornhuber and Deecke (1964, 1965). The potential shift immediately preceding movement corresponded with the NS' of Shibasaki et al. (1980). We identified, for the first time, a third shift intervening between BP and NS' and named it the intermediate shift (IS). The onset of BP occurred about 1.6 sec before EMG onset and was followed by IS which began about 875 msec before movement. The onset of NS' occurred 300 msec before EMG onset and terminated about 90 msec before this event. The slope of BP preceding right finger movement was steeper than that preceding left hand movement in all our right-handed subjects. The distribution of BP was symmetric about the midline. The IS potential shift had a slope which was steeper on the average preceding left finger movement than right. The distribution of IS was symmetric about the midline preceding left finger movement but had a contralateral tendency preceding right hand movement. NS' had a maximum slope at contralateral electrodes over the hand motor area and parietal areas. It was suggested that the BP potential shift originates in the supplementary motor area on the medial surface of the cerebral cortex. The differing distribution of the IS shift for the two hands suggests that this potential may be generated bilaterally preceding left finger movement but from the contralateral hemisphere only preceding movement of the right finger. The most likely origin of this potential was thought to be superior premotor cortex. NS' was considered to originate in primary motor cortex with possible contributions from other cortical areas associated with movement.     

The size of corpus callosum and functional connectivities of cortical regions in finger and shoulder movements

The correlations between the size of corpus callosum and the inter- and intra-hemispheric EEG coherence and the spatial EEG synchronization during finger and shoulder movements were analyzed in nine right-handed men. The cross-sectional surface areas of corpus callosum (CC) and of seven callosal regions were measured from the mid-sagittal slice of the anatomical MRI. Movement-related coherence between pairs of EEG electrodes overlying the central and parietal regions of both hemispheres was computed after spatially filtering EEG data by the Laplacian operator method. The spatial EEG synchronization was evaluated using omega-complexity, a novel measure which quantifies the number of independent sources of spontaneous EEG oscillations. The amplitude of coherence between the left and right S1/M1 areas after movement onset in the lower alpha band (7.8-9.8 Hz) correlated with the size of the callosal body in both types of movement. The size of the callosal body also correlated with the C3-Cz coherence in the 15.6-19.5 Hz band in finger movement, and in the 15.6-23.5 Hz band in shoulder movements. The size of the rostral, anterior intermediate and posterior intermediate truncus of CC correlated with omega-complexity in both types of movements indicating more foci of synchronized EEG oscillations in subjects with a large callosal truncus. The results suggest that the size of callosal truncus which is known to connect the primary sensorimotor and the supplementary motor areas of both hemispheres contributes to the coupling of EEG oscillations during voluntary finger and shoulder movements.     

Event-related desynchronization and excitability of the ipsilateral motor cortex during simple self-paced finger movements.

OBJECTIVE: To study the time course of oscillatory EEG activity and corticospinal excitability of the ipsilateral primary motor cortex (iM1) during self-paced phasic extension movements of fingers II-V. METHODS: We designed an experiment in which cortical activation, measured by spectral-power analysis of 28-channel EEG, and cortical excitability, measured by transcranial magnetic stimulation (TMS), were assessed during phasic self-paced extensions of the right fingers II-V in 28 right-handed subjects. TMS was delivered to iM1 0-1500 ms after movement onset. RESULTS: Ipsilateral event-related desynchronization (ERD) during finger movement was paralleled by increased cortical excitability of iM1 from 0-200 ms after movement onset and by increased intracortical facilitation (ICF) without changes in intracortical inhibition (ICI) or peripheral measures (F waves). TMS during periods of post-movement event-related synchronization (ERS) revealed no significant changes in cortical excitability in iM1. CONCLUSIONS: Our findings indicate that motor cortical ERD ipsilateral to the movement is associated with increased corticospinal excitability, while ERS is coupled with its removal. These data are compatible with the concept that iM1 contributes actively to motor control. No evidence for inhibitory modulation of iM1 was detected in association with self-paced phasic finger movements. SIGNIFICANCE: Understanding the physiological role of iM1 in motor control.     

Movement related cortical potentials of cued versus self-initiated movements: double dissociated modulation by dorsal premotor cortex versus supplementary motor area rTMS

The dorsal premotor cortex (PMd) is thought to play a significant role in movement preparation cued by sensory information rather than in self-initiated movements. The evidence in humans for this contention is still circumstantial. Here we explored the effects of modulation of PMd by excitability decreasing 1 Hz repetitive transcranial magnetic stimulation (rTMS) versus excitability increasing 5 Hz rTMS on two forms of movement related cortical potentials: contingent negative variation (CNV) versus Bereitschaftspotential (BP) reflecting externally cued versus self-triggered movement preparation. Ten healthy right-handed subjects performed visually cued or self-triggered simple sequential finger movements with their right hand. CNV and BP were recorded by 25 EEG electrodes covering the fronto-centro-parietal cortex and divided into an early (1500-500 ms before a go-signal or movement onset) and a late potential (500-0 ms). MRI-navigated 1 Hz rTMS of the left PMd resulted in significant increase of the late CNV over the left central region predominantly contralateral to the prepared right hand movement, while 5 Hz rTMS had no effect on CNV. In contrast, 1 and 5 Hz rTMS did not modify BP. Control experiments of 1 Hz rTMS of the supplementary motor area (SMA) and of low-intensity 1 Hz rTMS of the left primary motor cortex did not change CNV, but 1 Hz SMA-rTMS increased late BP. This double dissociation of effects of PMd-rTMS versus SMA-rTMS on CNV versus BP provides direct evidence that the left PMd in humans is more involved in preparatory processes of externally cued rather than self-initiated movements, contrasting with an opposite role of the SMA.     

Subthalamic nucleus stimulation reduces abnormal motor cortical overactivity in Parkinson disease

BACKGROUND: Based on the basal ganglia model, it has been hypothesized that the efficacy of high-frequency stimulation of the subthalamic nucleus (STN) against parkinsonian symptoms relies on the activation of cortical premotor regions. In previous positron emission tomography activation studies, STN high-frequency stimulation was associated with selective activation of midline premotor areas during hand movements but mainly reduced the regional cerebral blood flow in movement-related areas, peculiarly at rest. OBJECTIVE: To investigate with positron emission tomography the role of regional cerebral blood flow reduction in the clinical improvement provided by STN high-frequency stimulation. METHODS: Seven patients with advanced Parkinson disease, who were markedly improved by bilateral STN high-frequency stimulation, underwent positron emission tomography with H2(15)O while the right STN electrode was turned off. The patients were studied at rest and during right-hand movements in 3 electrode conditions: no stimulation, inefficient low-frequency stimulation, and efficient high-frequency stimulation. RESULTS: The main effect of high-frequency stimulation was to reduce regional cerebral blood flow in the left primary sensorimotor cortex, the lateral premotor cortex, the right cerebellum, and the midline premotor areas. The selective activation of the anterior cingulate cortex and the left primary sensorimotor cortex during hand movement under STN high-frequency stimulation was attributed to decreased regional cerebral blood flow at rest, rather than increased activation induced by STN high-frequency stimulation. Akinesia was correlated with the abnormal overactivity in the contralateral primary sensorimotor cortex and the ipsilateral cerebellum. CONCLUSION: High-frequency stimulation of the STN acts through the reduction of abnormal resting overactivity in the motor system, allowing selective cortical activation during movement.     

Interhemispheric transfer of voluntary motor commands in man

The lack of callosal fibres between homotopic areas of the hand in the sensorimotor cortex in man and its possible functional correlates were investigated in normal adult subjects by comparing simple reaction times (RTs) of voluntary movements triggered by a somaesthetic stimulus to the same or opposite side of the body. An air jet was delivered to the skin of distal (index finger) or proximal (shoulder) ipsi- or contralateral zones, and triggered voluntary extension of the index finger or flexion of the forearm. The RT was measured from the arrival of the stimulus to the skin to the onset of the surface EMG of the muscle extensor indicis proprius or biceps brachii. The RTs of the contralateral finger movements triggered by either proximal or distal skin stimuli were significantly longer than the RTs of the corresponding ipsilateral movements (mean difference 11.72 and 15.10 msec respectively). When the task was flexion of the forearm, the differences in RTs between contra- and ipsilateral movements were instead compatible with a transcallosal transfer (mean difference about 2 msec in both cases). It is concluded that transcallosal connections between hand sensorimotor areas are conceivably absent also in man. Furthermore, the delay in contralateral distal performance appears to be due to a lack of transfer of the command through the motor areas, rather than to a lack of transfer of the triggering cutaneous afferent information to the performing hemisphere.     

EEG correlates of finger movements as a function of range of motion and pre-loading conditions.

OBJECTIVES: The present study was designed to obtain additional data regarding the differential influence of kinematic parameters and different nominal force levels upon components of movement-related cortical potentials (MRP) during index finger flexion. METHODS: The absolute nominal force level of discrete movements was varied while the rate of force development remained constant within a given task. This was accomplished by utilizing a pre-loading experimental design at different ranges of index finger motion (25, 50 and 75 degrees), so that the movement kinematic profiles (velocity and acceleration) and rate of force development remained constant within each given range of motion. Time-domain averaging of EEG single trials was applied in order to extract 3 movement-related potentials (BP(-600 to -500), BP(-100 to 0) and N(0 to 100)) preceding and accompanying 25, 50 and 75 degrees of unilateral finger movement with no pre-load (0 g), small pre-load (100 g) and large pre-load (200 g). RESULTS: The range of motion differentially influenced the amplitude of early (BP(-600 to -500)) and late (BP(-100 to 0)) MRP components spatially localized over frontal, central and parietal areas. The amplitude of the N(0 to 100) component localized over parietal and frontal areas was also sensitive toward experimental manipulations of the range of motion. Overall, the amplitude of N(0 to 100) localized over the central area was the only MRP component that was sensitive to the amount of pre-loading. However, within a given range of motion, none of the pre-loading conditions (0, 100 or 200 g) influenced the amplitude of MRP components. CONCLUSIONS: The central finding was that an increase in nominal force production within a given range of motion did not influence MRP components when the rate of force development was held constant. It becomes especially apparent with strict control of kinematic and kinetic movement parameters that different methods of adding weight to the index finger performing the same movement patterns have different consequences for EEG correlates as reflected in the amplitude and spatial distribution of MRP. The range of motion of index finger flexion was the primary kinematic variable that consistently influenced MRP components both preceding and accompanying movement execution.     

Impairment of EEG desynchronisation before and during movement and its relation to bradykinesia in Parkinson's disease

OBJECTIVE: It has been suggested that the basal ganglia act to release cortical elements from idling (alpha) rhythms so that they may become coherent in the gamma range, thereby binding together those distributed activities necessary for the effective selection and execution of a motor act. This hypothesis was tested in 10 patients with idiopathic Parkinson's disease. METHODS: Surface EEG was recorded during self paced squeezing of the hand and elbow flexion performed separately, simultaneously, or sequentially. Recordings were made after overnight withdrawal of medication and, again, 1 hour after levodopa. The medication related improvement in EEG desynchronisation (in the 7.5-12.5 Hz band) over the 1 second before movement and during movement were separately correlated with the improvement in movement time for each electrode site. Correlation coefficients (r) > 0.632 were considered significant (p<0.05). RESULTS: Improvement in premovement desynchronisation correlated with reduction in bradykinesia over the contralateral sensorimotor cortex and supplementary motor area in flexion and squeeze, respectively. However, when both movements were combined either simultaneously or sequentially, this correlation shifted anteriorly, to areas overlying prefrontal cortex. Improvement in EEG desynchronisation during movement only correlated with reduction in bradykinesia in two tasks. Correlation was seen over the supplementary motor area during flexion, and central prefrontal and ipsilateral premotor areas during simultaneous flex and squeeze. CONCLUSIONS: The results are consistent with the idea that the basal ganglia liberate frontal cortex from idling rhythms, and that this effect is focused and specific in so far as it changes with the demands of the task. In particular, the effective selection and execution of more complex tasks is associated with changes over the prefrontal cortex.     

Neuromagnetic fields accompanying unilateral and bilateral voluntary movements: topography and analysis of cortical sources.

Movement-related magnetic fields (MRMFs) accompanying left and right unilateral and bilateral finger flexions were studied in 6 right-handed subjects. Six different MRMF components occurring prior to, and during both unilateral and bilateral movements are described: a slow pre-movement readiness field (RF, 1-0.5 sec prior to movement onset); a motor field (MF) starting shortly before EMG onset; 3 separate "movement-evoked" fields following EMG onset (MEFI at 100 msec; MEFII at 225 msec; and MEFIII at 320 msec); and a "post-movement" field (PMF) following the movement itself. The bilateral topography of the RF and MF for both unilateral and bilateral movements suggested bilateral generators for both conditions. Least-squares fitting of equivalent current dipole sources also indicated bilateral sources for MF prior to both unilateral and bilateral movements with significantly greater strength of contralateral sources in the case of unilateral movements. Differences in pre-movement field patterns for left versus right unilateral movements indicated possible cerebral dominance effects as well. A single current dipole in the contralateral sensorimotor cortex could account for the MEFI for unilateral movements and bilateral sensorimotor sources for bilateral movements. Other MRMF components following EMG onset indicated similar sources in sensorimotor cortex related to sensory feedback or internal monitoring of the movement. The results are discussed with respect to the possible generators active in sensorimotor cortex during unilateral and bilateral movement preparation and execution and their significance for the study of cortical organization of voluntary movement.     

Somatotopy in the Human Motor Cortex Hand Area. A High-Resolution Functional MRI Study

Fine-scale somatotopic encoding in brain areas devoted to sensorimotor processing has recently been questioned by functional neuroimaging studies which suggested its absence within the hand area of the human primary motor cortex. We re-examined this issue by addressing somatotopy both in terms of functional segregation and of cortical response preference using oxygenation-sensitive magnetic resonance imaging at high spatial resolution. In a first step, spatial representations of self-paced isolated finger movements were mapped by using motor rest as a control state. A subsequent experimental design studied the predominance of individual finger movements by using contrasting finger movements as the control task. While the first approach confirmed previous reports of extensive overlap in spatial representations, the second approach revealed foci of differential activation which displayed an orderly mediolateral progression in accordance with the classical cortical motor homunculus. We conclude that somatotopy within the hand area of the primary motor cortex does not present as qualitative functional segregation but as quantitative predominance of certain movement or digit representation embedded in an overall joint hand area.     

Coregistration of EEG and fMRI in a simple motor task

The purpose of this study was to evaluate the adequacy of coregistration of movement-related cortical potentials (MRCPs) and functional magnetic resonance imaging (fMRI) data in the primary sensorimotor cortex. Data were acquired in four normal subjects during right and left simple index finger movements. In fMRI (single-slice, 1.5 Tesla, T2^*-weighted FLASH sequence), contralateral primary motor (M1) and primary sensory cortex (S1) were activated in all subjects. Spatiotemporal dipole modelling of electric MRCP generators (BESA) revealed two main sources in the central region contralateral to the moving finger. Both sources were tangentially oriented. Their configuration was consistent with source locations in the anterior (M1) and posterior (S1) banks of the central sulcus. Accordingly, the M1 source generated the pre-movement, the S1 source largely the immediate post-movement MRCP component. Taken together, MRCP modelling and fMRI data indicated a phasic sequential activation pattern of mostly sulcal portions of contralateral M1 and S1. After coregistration of anatomical MRI, fMRI, and dipole modelling results, the average 3D-distance between fMRI activation areas and MRCP source locations was 18.6 mm (SD 7.6), with the largest deviation in the anterior-posterior direction (12.1 ± 9.5 mm). Coregistration inaccuracies of similar magnitude (∼ 17 mm) have been reported previously with MEG and PET or fMRI. We conclude, therefore, that the combination of EEG and fMRI is a promising technique for validation of electrophysiological source models and for evaluation of human functional brain anatomy with both adequate spatial and temporal resolution. © 1996 Wiley-Liss, Inc.