Movement-evoked Field Research Articles

Attention directed to proprioceptive stimulation alters its cortical processing in the primary sensorimotor cortex.

Movement-evoked fields to passive movements and corticokinematic coherence between limb kinematics and magnetoencephalographic signals can both be used to quantify the degree of cortical processing of proprioceptive afference. We examined in 20 young healthy volunteers whether processing of proprioceptive afference in the primary sensorimotor cortex is modulated by attention directed to the proprioceptive stimulation of the right index finger using a pneumatic-movement actuator to evoke continuous 3-Hz movement for 12 min. The participant attended either to a visual (detected change of fixation cross colour) or movement (detected missing movements) events. The attentional task alternated every 3-min. Coherence was computed between index-finger acceleration and magnetoencephalographic signals, and sustained-movement-evoked fields were averaged with respect to the movement onsets every 333ms. Attention to the proprioceptive stimulation supressed the sensorimotor beta power (by ~12%), enhanced movement-evoked field amplitude (by ~16%) and reduced corticokinematic coherence strength (by ~9%) with respect to the visual task. Coherence peaked at the primary sensorimotor cortex contralateral to the proprioceptive stimulation. Our results indicated that early processing of proprioceptive afference in the primary sensorimotor cortex is modulated by inter-modal directed attention in healthy individuals. Therefore, possible attentional effects on corticokinematic coherence and movement-evoked fields should be considered when using them to study cortical proprioception in conditions introducing attentional variation.

Motor Action Execution in Reaction-Time Movements: Magnetoencephalographic Study.

Reaction-time movements are internally planned in the brain. Presumably, proactive control in reaction-time movements appears as an inhibitory phase preceding movement execution. We identified the brain activity of reaction-time movements in close proximity to movement onset and compared it with similar self-paced voluntary movements without external command. We recorded 18 healthy participants performing reaction-time and self-paced fast index finger abductions with 306-sensor magnetoencephalography and electromyography. Reaction-time movements were performed as responses to cutaneous electrical stimulation delivered on the hand radial nerve area. Motor field and movement-evoked field 1 corresponding to the sensorimotor cortex activity during motor execution and afferent feedback after the movement were analyzed with Brainstorm's scouts using regions of interest analysis. Primary motor and somato sensory cortices were active before and after movement onset. During reaction-time movements, primary motor and somato sensory cortices showed higher activation compared with self-paced movements. In primary motor cortex, stronger preparatory activity was seen in self-paced than in reaction time task. Both primary motor and somato sensory cortices participated in the movement execution and in the prediction of sensory consequences of movement. Cutaneous stimulation facilitated cortical activation during motor field after reaction-time movements, implying the applicability of cutaneous stimulation in motor rehabilitation.

Symptom-associated change of motor-related neuromagnetic fields in a patient with multiple sclerosis: A case report

The objective of this study was to investigate functional abnormalities of the brain in a patient with multiple sclerosis (MS) by using magnetoencephalography (MEG) and a finger-tapping task. A 46-year-old woman that presented with motor weakness of left hand and was diagnosed with MS. Conventional magnetic resonance imaging demonstrated a white matter lesion with hyperintensity on T2-weighted images in the right motor area. MEG recordings were performed during the period of motor weakness and after clinical improvement. Neuromagnetic brain activation was elicited by a simple, visually cued finger movement. The Equivalent current dipole (ECD) strength of the movement-evoked field (MEF) in the affected hemisphere was significantly decreased relative to the unaffected hemisphere. After improvement in motor weakness, we found that the lower amplitude of the readiness field and decreased ECD strength of the MEF observed in affected hemisphere during motor weakness had recovered. Analysis of motor-related neuromagnetic fields revealed that MEG may be used to detect diffuse changes in the brain that are not observable by conventional imaging of white matter regions in MS. We further found that brain activities can change after improvement in motor weakness.

Genetic and environmental influences on motor function: a magnetoencephalographic study of twins.

To investigate the effect of genetic and environmental influences on cerebral motor function, we determined similarities and differences of movement-related cortical fields (MRCFs) in middle-aged and elderly monozygotic (MZ) twins. MRCFs were measured using a 160-channel magnetoencephalogram system when MZ twins were instructed to repeat lifting of the right index finger. We compared latency, amplitude, dipole location, and dipole intensity of movement-evoked field 1 (MEF1) between 16 MZ twins and 16 pairs of genetically unrelated pairs. Differences in latency and dipole location between MZ twins were significantly less than those between unrelated age-matched pairs. However, amplitude and dipole intensity were not significantly different. These results suggest that the latency and dipole location of MEF1 are determined early in life by genetic and early common environmental factors, whereas amplitude and dipole intensity are influenced by long-term environmental factors. Improved understanding of genetic and environmental factors that influence cerebral motor function may contribute to evaluation and improvement for individual motor function.

Activation of the Human Premotor Cortex During Motor Preparation in Visuomotor Tasks

Functional brain mapping studies in humans suggest that both motor and premotor cortices interact during movement execution. The aim of this study was to investigate whether the premotor cortex also participates in motor planning. We measured movement-related cerebral fields (MRCFs) using magnetoencephalography from the left hemisphere of 12 healthy right-handed participants during two simple visuomotor tasks cued by two visual stimuli S1 and S2. Participants performed a unilateral task in which they always extended the right index finger after S2 presentation regardless of the color of S1 and a bilateral task in which they extended either the right or left index finger after S2 presentation according to the color of S1. Significantly higher MRCF activity was observed during the 500ms S1 to S2 interval in the bilateral task than in the unilateral task. In the bilateral task trials, the latency of the peak MRCF during the S1 to S2 interval was 343.9±73.5ms after S1 presentation and that of the peak of movement-evoked field 1 was 33.4±3.9ms after movement onset in the bilateral task. Equivalent current dipoles at the peak MRCF were significantly medial (9.2±12.1mm) and anterior (19.8±6.9mm) to the reference location in the somatosensory cortex (area 3b) established by median nerve stimulation. This location corresponds to the dorsal premotor cortex. These findings suggest that activation of the premotor cortex observed during the interstimulus interval may represent a neurophysiological marker of response selection.

Increased sensory feedback in Tourette syndrome

Tourette syndrome (TS) is a neuro-psychiatric disorder being characterized by motor and phonic tics typically preceded by sensory urges. Given the latter the role of the sensory system and sensorimotor interaction in TS has recently gained increased attention. 12 TS patients and 12 matched control subjects performed two tasks, requiring simple finger movements: a Go/NoGo task and a self paced movement task. Neurophysiological data was recorded using magnetoencephalography (MEG). Event related responses around movement onset, i.e. motor field (MF) occurring directly prior to the movement and movement evoked field (MEF) immediately after movement onset were analyzed using dipole modeling. MF peak amplitudes did not differ between groups in either task. In contrast, in both tasks MEF peak amplitudes were increased in TS patients. Moreover, larger MEF amplitudes during self paced movements were inversely correlated with motor tic frequency and severity. Enlarged MEF amplitudes as a marker of early sensory feedback of one's own movements probably represent enlarged sensory input from the periphery resulting from altered subcortical gating. We conclude that TS patients exhibit altered sensory-motor processing involved in voluntary movement control, which might also be successful in tic control.

Movement-related neuromagnetic fields and performances of single trial classifications

In order to clarify whether neurophysiological profiles affect the performance of brain machine interfaces (BMI), we examined the relationships between amplitudes of movement-related cortical fields (MRCFs) and decoding performances during movement. Neuromagnetic activities were recorded in nine healthy participants during three types of unilateral upper limb movements. The movement types were inferred by a support vector machine. The amplitude of MRCF components, motor field (MF), movement-evoked field I (MEFI), and movement-evoked field II (MEFII) were compared with the decoding accuracies in all participants. Decoding accuracies at the latencies of MF, MEFI, and MEFII surpassed the chance level in all participants. In particular, accuracies at MEFI and MEFII were significantly higher in comparison with that of MF. The amplitudes and decoding accuracies were strongly correlated (MF, r(s)=0.90; MEFI, r(s)=0.90; and MEFII, r(s)=0.87). Our results show that the variation of MRCF components among participants reflects decoding performance. Neurophysiological profiles may serve as a predictor of individual BMI performance and assist in the improvement of general BMI performance.

Neural compensation mechanisms to regulate motor output during physical fatigue

Central fatigue refers to a progressive decline in the ability to activate muscles voluntarily. Although the neural mechanisms of central inhibition of the motor area during physical fatigue have been widely investigated, mechanisms supporting motor output during fatigue remain to be clarified. In this study, the compensation mechanisms to regulate physical fatigue were examined using a 160-channel whole-head-type magnetoencephalographic (MEG) system. The study group consisted of nine right-handed healthy participants. After enrollment, participants performed a fatigue-inducing physical task session in which they performed repetitive grips of the right hand at maximal voluntary contraction levels every second. Before and after the session, imagery of maximum grips of the right hand was performed for evaluation with MEG. Although beta-band event-related desynchronization (ERD) level of the motor movement-evoked magnetic field in the left sensorimotor area showed a trend toward reduction after the fatigue session, the ERD level of the motor movement-evoked magnetic field in the right sensorimotor area was increased after the session. The ERD level in the prefrontal area was increased after the fatigue-inducing session. The ERD level in the left sensorimotor area was positively associated with that in the right sensorimotor area after the fatigue-inducing task session. In addition, ERD levels in the left and right sensorimotor areas had trends toward positive correlations with that in the prefrontal area. These results suggest that the ipsilateral sensorimotor and prefrontal areas are brain regions associated with compensation mechanisms to support motor output under the condition of physical fatigue.

Source analysis of the magnetic field evoked during self-paced finger movements

Objective: The aim of this study is to investigate a source of cortical magnetic fields evoked by index finger movements.Methods: We analysed both movement-related cortical fields (MRCFs) and somatosensory-evoked fields (SEFs) by single equivalent current dipole (ECD) method in six healthy subjects. Dipole locations were superimposed on MR images of each individual subject.Results: The first component after finger movement (movement-evoked field I, MEFI) was observed in all subjects. The dipole of MEFI was oriented posteriorly, and was located on the posterior wall of the central sulcus of the hemisphere contralateral to the movement. The SEFs showed three major components: N20m, P30m and P60m. The dipoles of P30m and P60m were orientated posteriorly, similarly to the MEFI dipole, while that of N20m was orientated anteriorly. The dipole location of MEFI was closely located to P60m, not to N20m and P30m. The mean location of the MEFI dipole was significantly (p<0.05) superior to N20m.Conclusion: These findings suggest that MEFI would be generated in the sensory area (area 3b) affected by multiple afferents and activities, and that the source of the MEFI is not identical to that of the N20m component.

Cortical neuromagnetic activation accompanying two types of voluntary finger extension

We examined the amplitude and latency of movement-related cerebral field (MRCF) waveforms, the generator and afferent feedback of movement-evoked field 1 (MEF1), and the relationship between motor field neuromagnetic activity and electromyographic activity during performance of two types of voluntary index extension. Eight healthy, right-handed male volunteers participated in this study. Experiments for each subject consisted of recording of MRCFs following two types of finger movement. One (Task 1) involved voluntary extension of the right index finger to about 40°. In the second (Task 2), an elastic band was placed on the right index fingertip, producing a resistance of about 1.5 times the electromyographic activity associated with the voluntary movement yielding extension to approximately 40°. Peak amplitude and the ECD moment of the motor field differed significantly between the two tasks. In Task 2, the electromechanical delay from EMG onset to movement onset (77.8 ± 16.2) was longer than in Task 1 (44.4 ± 10.4). However, the latency from EMG onset to MEF1 peak was 87.6 ± 8.5 ms in Task 2, and did not differ significantly from that in Task 1 (88.6 ± 8.5). The ECDs of MEF1 were located significantly medial to N20 m and lateral and posterior to the motor field. These findings suggest that the ECD of MEF1 is located in area 3b, but is slightly different from N20 m, and that this MEF1 component activation is due not to the onset of joint movement but to that of muscular contraction.

Motor field sensitivity for preoperative localization of motor cortex

In this study the role of magnetic source imaging for preoperative motor mapping was evaluated by using a single-dipole localization method to analyze motor field data in 41 patients. Data from affected and unaffected hemispheres were collected in patients performing voluntary finger flexion movements. Somatosensory evoked field (SSEF) data were also obtained using tactile stimulation. Dipole localization using motor field (MF) data was successful in only 49% of patients, whereas localization with movement-evoked field (MEF) data was successful in 66% of patients. When the spatial distribution of MF and MEF dipoles in relation to SSEF dipoles was analyzed, the motor dipoles were not spatially distinct from somatosensory dipoles. The findings in this study suggest that single-dipole localization for the analysis of motor data is not sufficiently sensitive and is nonspecific, and thus not clinically useful.

Neuromagnetic motor fields accompanying self-paced rhythmic finger movement at different rates

We have studied the effect of movement rate on MEG activity associated with self-paced finger movement in four subjects to determine whether the amplitude or latency of motor-evoked activity changes across a range of rates. Subjects performed a continuation paradigm at 21 distinct rates (range: 0.5-2.5 Hz) chosen because of their relevance for many types of sensorimotor coordination (e.g. musical performance). Results revealed a pair of field patterns whose topography and temporal dynamics were similar across all subjects. The strongest pattern was a movement-evoked field (MEF) that emerged during the response and exhibited one or two polarity reversals in time depending on the subject. The MEF complex was tightly coupled to the biphasic response profile but neither latency nor peak amplitude of each MEF component had significant dependence on the temporal duration between successive responses, i.e. movement rate. In contrast, the maximal amplitude of a second, weaker pattern decreased by over 50% when movement rates exceeded 1.1 Hz (inter-response interval <1 s). This pattern was characterized by a change in field line direction over the midline of the scalp and a gradual accumulation of amplitude prior to movement onset. Both characteristics are suggestive of a readiness field. The observed rate-dependent changes in this field may contribute to known transitions in sensorimotor coordination that emerge when the frequency of coordination is increased.

Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event-related beamforming approach.

We describe a novel spatial filtering approach to the localization of cortical activity accompanying voluntary movements. The synthetic aperture magnetometry (SAM) minimum-variance beamformer algorithm was used to compute spatial filters three-dimensionally over the entire brain from single trial neuromagnetic recordings of subjects performing self-paced index finger movements. Images of instantaneous source power ("event-related SAM") computed at selected latencies revealed activation of multiple cortical motor areas prior to and following left and right index finger movements in individual subjects, even in the presence of low-frequency noise (e.g., eye movements). A slow premovement motor field (MF) reaching maximal amplitude approximately 50 ms prior to movement onset was localized to the hand area of contralateral precentral gyrus, followed by activity in the contralateral postcentral gyrus at 40 ms, corresponding to the first movement-evoked field (MEFI). A novel finding was a second activation of the precentral gyrus at a latency of approximately 150 ms, corresponding to the second movement-evoked field (MEFII). Group averaging of spatially normalized images indicated additional premovement activity in the ipsilateral precentral gyrus and the left inferior parietal cortex for both left and right finger movements. Weaker activations were also observed in bilateral premotor areas and the supplementary motor area. These results show that event-related beamforming provides a robust method for studying complex patterns of time-locked cortical activity accompanying voluntary movements, and offers a new approach for the localization of multiple cortical sources derived from neuromagnetic recordings in single subject and group data.

Cortical activation in area 3b related to finger movement: an MEG study.

To evaluate cortical activation reflecting sensory feedback after finger movement, we recorded movement-related cerebral fields (MRCFs) following voluntary finger movement and somatosensory evoked fields for mixed (median) and pure cutaneous (radial) nerve stimulations (mSEFs and rSEFs) in six normal subjects. Equivalent current dipoles for movement-evoked field 1 (MEF1) in MRCFs and the component (70m) obtained in mSEFs, not clearly in rSEFs, were similarly distributed in each subject. They were located in area 3b, but both mean locations were significantly (p < 0.01) medial to N20m in mSEFs. MEF1 and 70m reflect similar cortical activities related to finger movement and have the same neuronal generator in area 3b, which is different from that of N20m.

Analysis of the source in the sensory area during self-paced finger movements

The movement-related cortical fields (MRCFs) accompanying index finger movements and somatosensory-evoked fields (SEFs) were investigated in 10 subjects. Movement-evoked field (MEFI) was observed in all of the subjects. The dipole of MEFI was directed posteriorly and was located in the postcentral gyrus of the hemisphere contralateral to the movement. The SEFs showed three major components: N20m, P30m and P60m. The direction of the MEFI dipole was similar to that of P30m and P60m. Based on the distribution of the dipole locations, MEFI was similar to P60m and different from P30m. The mean location of the MEFI dipole was more posterior and medial than the dipole position of P30m and P60m. It suggests that MEFI was generated by the higher sensory area.

Bilateral neuromagnetic activation of human primary sensorimotor cortex in preparation and execution of unilateral voluntary finger movements

Extracranial magnetoencephalographic activity was separately recorded (25 channels) from bilateral primary sensorimotor cortex (M1–S1) of normal right-handers during unilateral finger movements. Standard dipole analysis indicated only a contralateral M1–S1 source for first movement-evoked field (MEF1) peaking at about 115 ms after electromyographic onset. However, the subtraction of the magnetic field generated by this source from the recorded magnetic field disclosed a low-amplitude ipsilateral central-parietal MEF1 that was explained by an ipsilateral M1–S1 source.

Sensory feedback contributes to early movement-evoked fields during voluntary finger movements in humans

Neuromagnetic field changes accompanying voluntary movement in humans (`movement-evoked fields' or MEFs) were recorded over the scalp using a whole-head MEG system during the performance of self-paced finger movements in order to determine the contribution of sensory feedback to the generation of these brain responses. It was found that cooling the subject's arm resulted in delays of 8 ms or more in the latency of the early movement-evoked field component (MEFI). These delays were attributed to increases in conduction times in the afferent pathways as confirmed by electrically evoked somatosensory responses and suggest a peripheral origin of the MEFI. In a second experiment, we demonstrated the effects of sensory input to the contralateral hand during a simple button pressing task in 4 subjects. The results indicated that responses over the hemisphere ipsilateral to the side of movement which resembled previously reported ipsilateral MEFs can be elicited by the spread of mechanical stimulation to opposite side of the body when a mechanical trigger is used. These experiments provide further evidence that early movement-evoked fields produced by unilateral finger movements are observed primarily over the contralateral somatosensory cortex and represent sensory feedback to the somatosensory cortex from the periphery.

Reliability of Dipole Localization for the Movement-Evoked Field Component MEF I

The movement-evoked field I (MEF I) component is the largest and most stable neuromagnetic component accompanying self-paced movements. In order to use MEG for studying dynamic changes in the cortical organization of movements, data about the reliability and variability of these neuromagnetic components for individual subjects must be established during different sessions. For this aim, three male subjects were requested to perform self-paced flexions of their index finger and thumb in repeated sessions while the MEG was recorded by a 31 channel system. The MEF I was identified for each session and a single equivalent dipole was calculated for this component. The dipole localizations of the various sessions were compared. The standard deviation of the localization for all persons and all values amounts to 4.0-5.2 mm for the three spatial dimensions. Our data suggest that the spatial distance between two single focal sources fitted to the MEF I must be greater than 14 mm to be interpreted as distinct. However, the neuromagnetic field structure and the resulting dipole localization of the MEF I component are quite stable and could be used for the evaluation of cortical plasticity.

Neuromagnetic study of movement-related changes in rhythmic brain activity

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated in a typical Bereitschaftspotential paradigm consisting of self-paced voluntary movement of the right index finger. To assess movement-related spectral changes of the spontaneous magnetoencephalogram, latency- dependent short-time spectra were obtained by Fourier analysis for each single trial. The number of trials in which the spectral estimate for a certain frequency and latency deviated from reference values was then transformed into a probabilistic relative power measure. A spectral power depression around 20 Hz was observed starting about 2.5 s before movement onset, followed by elevated power in the 20–35 Hz range starting about 500 ms after movement onset. Generally, the power increase differed from the prior depression in both spectrum and topography, suggesting different generating processes rather than just a ‘rebound’ effect of the idling rhythm generator. The time course and topography of spectral power changes are discussed in relation to the corresponding properties of the movement-related neuromagnetic fields (readiness field, motor field, and movement-evoked field 1).

Neuromagnetic study of movement-related changes in rhythmic brain activity

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated in a typical Bereitschaftspotential paradigm consisting of self-paced voluntary movement of the right index finger. To assess movement-related spectral changes of the spontaneous magnetoencephalogram, latency- dependent short-time spectra were obtained by Fourier analysis for each single trial. The number of trials in which the spectral estimate for a certain frequency and latency deviated from reference values was then transformed into a probabilistic relative power measure. A spectral power depression around 20 Hz was observed starting about 2.5 s before movement onset, followed by elevated power in the 20–35 Hz range starting about 500 ms after movement onset. Generally, the power increase differed from the prior depression in both spectrum and topography, suggesting different generating processes rather than just a ‘rebound’ effect of the idling rhythm generator. The time course and topography of spectral power changes are discussed in relation to the corresponding properties of the movement-related neuromagnetic fields (readiness field, motor field, and movement-evoked field 1).