Evaluation of event-related desynchronization (ERD) preceding and following voluntary self-paced movement.

A method of accurate storage and on-line preprocessing of an EEG signal, preceding and following a trigger signal, elicited by button pressing, is described. The method was used to study the changes occurring in the power of the rhythmic activity within the alpha band in central areas, during voluntary, self-paced movement in 10 normal humans. A short-lasting decrease or phasic event-related desynchronization (ERD) of alpha power, representing mu activity, was observed in all 10 subjects. During the 2 sec period preceding movement the phasic ERD was mostly bilateral, but larger prior to right than to left thumb movement. At onset and during the first second of execution of movement, the phasic ERD was mostly bilateral but predominant in ipsilateral areas. Preceding or during movement, maximum ERD was observed in most cases in central-vertex regions.     

Simultaneous EEG 10 Hz desynchronization and 40 Hz synchronization during finger movements.

Nineteen-channel EEG was recorded with closely spaced electrodes overlaying the left sensorimotor cortex during self-paced, voluntary right finger movements. Three right-handed people served as subjects. The EEG was analysed in the 10 Hz band (10-12 Hz) and in four 40 Hz bands (34-36, 36-38, 38-40, 40-42) by calculation of ERD time courses and ERD maps, whereby a ERD is characterized by a movement-related band power decrease. In all three subjects a close to C3 localized 10 Hz ERD was found, starting about 2 s prior to movement onset and continuing during movement. Along with this 10 Hz ERD a localized and short-lasting (about 0.5 s) burst of 40 Hz oscillations was embedded around movement onset. This can be interpreted as indicating that planning of movement is accompanied by a desynchronization of central mu rhythm and a generation of 40 Hz oscillations.     

Transient human cortical responses during the observation of simple finger movements: a high-resolution EEG study

High-resolution event-related potentials (ERPs) were used to model the hemispherical representation of the transient cortical responses relating to the observation of movement during execution (right or left aimless finger extension). Subjects were seated in front of the observed person and looked at both their own and the observer's hand to receive similar visual feedback during the two conditions. In a visual control condition, a diode light moved at the observed person's hand. A first potential accompanying the movement execution peaked at about +110 msec over the contralateral somatomotor areas. It was followed by a potential (P300) peaking at about +350 msec over the central midline. In contrast, the potentials accompanying the movement observation peaked later over parietal-occipital other than somatomotor areas (N200 peak, +200 msec; P300 peak, +400 msec). Notably, the N200 was maximum in left parietal area whereas the P300 was maximum in right parietal area regardless the side of the movement. They markedly differed by the potentials following the displacement of the diode light. These results suggest a rapid time evolution (approximately 200-400 msec) of the cortical responses characterizing the observation of aimless movements (as opposite to grasping or handling). The execution of these movements would mainly involve somatomotor cortical responses and would be scarcely founded on the visual feedback. In contrast, the observation of the same movements carried out by others would require dynamical responses of somatomotor and parietal-occipital areas (especially of the right hemisphere), possibly for a stringent visuospatial analysis of the motor event.     

On the time resolution of event-related desynchronization: a simulation study.

OBJECTIVES: To investigate the time resolution of different methods for the computation of event-related desynchronization/synchronization (ERD/ERS), including one based on Hilbert transform. METHODS: In order to better understand the time resolution of ERD/ERS, which is a function of factors such as the exact computation method, the frequency under study, the number of trials, and the sampling frequency, we simulated sudden changes in oscillation amplitude as well as very short and closely spaced events. RESULTS: Hilbert-based ERD yields very similar results to ERD integrated over predefined time intervals (block ERD), if the block length is half the period length of the studied frequency. ERD predicts the onset of a change in oscillation amplitude with an error margin of only 10-30 ms. On the other hand, the time the ERD response needs to climb to its full height after a sudden change in oscillation amplitude is quite long, i.e. between 200 and 500 ms. With respect to sensitivity to short oscillatory events, the ratio between sampling frequency and electroencephalographic frequency band plays a major role. CONCLUSIONS: (1) The optimal time interval for the computation of block ERD is half a period of the frequency under investigation. (2) Due to the slow impulse response, amplitude effects in the ERD may in reality be caused by duration differences. (3) Although ERD based on the Hilbert transform does not yield any significant advantages over classical ERD in terms of time resolution, it has some important practical advantages.     

Motor programming is more affected in progressive supranuclear palsy than in Parkinson's disease: a spatiotemporal study of event-related desynchronization.

To determine the benefit of motor programming analysis for distinguishing patients with parkinsonism, we compared the spatiotemporal pattern of event-related desynchronization (ERD) preceding a self-paced voluntary wrist flexion between two groups of 10 patients with progressive supranuclear palsy (PSP) and Parkinson's disease (PD) and 10 control subjects. ERD of the mu rhythm was computed from 11 source derivations covering the medial frontocentral, central, and parietocentral areas during two successive left and right experimental conditions (80 self-paced wrist flexions). ERD began in the control group 1750 ms before movement onset over the contralateral central area and then appeared bilaterally on movement execution. In both patient groups, spatiotemporal distribution differed from that in the control group. In the PSP group, ERD had a shorter latency over the contralateral primary sensorimotor area compared with the PD group (PSP: 375 ms before movement onset for both conditions; PD: right flexion 1125 ms before movement onset, left flexion 1000 ms). ERD was observed over the parietocentral area in both groups but also with a clear reduction of latency before movement onset in the PSP group. In both groups, a bilateral central pattern appeared 250 ms before movement execution. In conclusion, our study indicates that ERD analysis is a useful method for observing the changes in cortical activation and for measuring motor programming impairment in parkinsonism, which was more affected in PSP than in PD.     

The effects of memory load on event-related EEG desynchronization and synchronization.

OBJECTIVES: To examine the effects of working memory load on the event-related desynchronization (ERD) and synchronization (ERS) of several narrow EEG frequency bands. METHODS: ERD/ERS responses of the 4-6, 6-8, 8-10 and 10-12 Hz EEG frequency bands were studied in 24 normal subjects performing a visual sequential letter task (so-called n-back task) in which memory load was varied from 0 to 2. RESULTS: In the 4-6 Hz theta frequency band, a long-lasting synchronization was observed in the anterior electrodes, especially after the presentation of targets. In the 6-8 and 8-10 Hz frequency bands, anterior ERS was elicited especially in the 2-back condition (highest memory load). In contrast to the responses of the 8-10 Hz frequency band, in the 10-12 Hz frequency band the 2-back experimental condition elicited the greatest ERD. CONCLUSIONS: In the highest memory load (2-back) experimental condition the attentional capacities were most probably exceeded, resulting in 6-8 and 8-10 Hz ERS. This might reflect an inhibition of such brain areas (frontal cortices) no longer involved in task completion when alternative strategies are needed and utilized. These more 'cognitive' strategies were then reflected as an increase in 10-12 Hz ERD. Additionally, our results support the assumption that the simultaneously recorded ERD/ERS responses of different narrow EEG frequency bands differ and reflect distinct aspects of information processing.     

Lateralization of event-related beta desynchronization in the EEG during pre-cued reaction time tasks.

OBJECTIVE: Here, we investigate whether the event-related desynchronization (ERD) of spectral components of the cortical EEG in the beta (13-30 Hz) frequency range may, in part, index motor selection processes. Specifically, we sought evidence for a contralaterally dominant component of the beta ERD that is limited to trials in which motor selection is possible prior to any imperative cue to move, with attendant behavioural advantage. METHODS: We measured reaction time and assessed the lateralization of beta ERD in 12 healthy volunteers as they performed pre-cued choice reaction time tasks, in which warning S1 cues were either fully predictive about the laterality of a subsequent imperative S2 signal or provided no laterality information. We calculated 'lateralized ERD index' (LERDI), a parallel measure to the lateralized readiness potential in the time domain. RESULTS: Trials with 100% S1-S2 congruency produced significantly shorter reaction times than trials with 50% S1-S2 congruency, where laterality information was unreliable. Beta LERDI indicated significantly greater lateralisation of the ERD in the warning-go interval and of event-related synchronization (ERS) following movement in the 100% condition than in the 50% condition. The lateralization of the beta ERD with respect to hand persisted, even when subjects were instructed to make movements of opposite laterality to those prompted. CONCLUSIONS: Lateralized EEG changes occur in the beta band in the S1-S2 interval prior to movement, but only when informative warning cues allow early motor selection, as suggested by the shortening of reaction time. Furthermore, the enhanced contralateral ERS with 100% S1-S2 congruency suggests that this phenomenon is at least partly independent of afferent feedback, as the same movement was made in the 100 and 50% conditions. SIGNIFICANCE: Lateralized suppression of beta power prior to externally generated movements is associated with motor selection.     

Movement-related desynchronization of alpha rhythms is lower in athletes than non-athletes: A high-resolution EEG study

ObjectiveThe “neural efficiency” hypothesis posits that neural activity is reduced in experts. Here we tested the hypothesis that compared with non-athletes, elite athletes are characterized by a reduced cortical activation during simple voluntary movement and that this is reflected by the modulation of dominant alpha rhythms (8–12 Hz).MethodsEEG data (56 channels; EB-Neuro) were continuously recorded in the following right-handed subjects: 10 elite karate athletes and 12 non-athletes. During the EEG recordings, they performed brisk voluntary wrist extensions of the right or left hand (right movement and left movement). The EEG cortical sources were estimated by standardized low-resolution brain electromagnetic tomography (sLORETA) freeware. With reference to a baseline period, the power decrease of alpha rhythms during the motor preparation and execution indexed the cortical activation (event-related desynchronization, ERD).ResultsDuring both preparation and execution of the right movements, the low- (about 8–10 Hz) and high-frequency alpha ERD (about 10–12 Hz) was lower in amplitude in primary motor area, in lateral and medial premotor areas in the elite karate athletes than in the non-athletes. For the left movement, only the high-frequency alpha ERD during the motor execution was lower in the elite karate athletes than in the non-athletes.ConclusionsThese results confirmed that compared with non-athletes, elite athletes are characterized by a reduced cortical activation during simple voluntary movement.SignificanceCortical alpha rhythms are implicated in the “neural efficiency” of athletes’ motor systems.     

Movement preparation is affected by tissue damage in multiple sclerosis: evidence from EEG event-related desynchronization.

OBJECTIVE: To investigate the impact of brain tissue damage in Multiple Sclerosis (MS) on the efficiency of programming of voluntary movement, assessed using event-related desynchronization of the EEG. METHODS: The onset latency of mu ERD (percent desyncronization of the mu rhythm preceding movement onset) to hand movement was studied in 34 MS patients. ERD onset was compared with normative data and correlated with T1 and T2 total lesion volume (TLV) at magnetic resonance imaging (MRI). RESULTS: ERD onset latency was significantly correlated with T1-TLV (r = 0.53, P = 0.001) and T2 lesion load (r = 0.5, P = 0.003), even after correcting for disability. Patients with higher T1-TLV had significantly delayed ERD onset compared with normal subjects and with patients with lower T1-TLV; patients with higher T2-TLV had significantly delayed ERD compared with normal subjects only. ERD onset latency was not correlated to clinical disability. CONCLUSIONS: Our finding of delayed ERD onset in patients with more severe measures of brain damage, independently from clinical disability, suggests that functional cortico-cortical and cortico-subcortical connections underlying the expression of ERD during programming of voluntary movement are disrupted by the MS related pathological process. Further, studies are needed to evaluate the role of specific anatomical cortico-subcortical circuits in determining this abnormality. SIGNIFICANCE: The extent of brain lesion load in multiple sclerosis affects cortical changes related to motor preparation, detected by analysis of onset latency of event-related desynchronization (ERD) of the mu rhythm to self-paced movement.     

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.     

Temporal evolution of event-related desynchronization in acute stroke: A pilot study

ObjectiveAssessment of event-related desynchronization (ERD) may assist in predicting recovery from stroke and rehabilitation, for instance in BCI applications. Here, we explore the temporal evolution of ERD during stroke recovery.MethodsTen stroke patients and eleven healthy controls were recruited to participate in a hand movement task while EEG was being recorded. Four measurements were conducted in eight patients within four months. We quantified changes of ERD using a modulation strength measure, S_m, which represents an area and amplitude of ERD.Results7/8 patients showed good recovery. Absence-or-reduction of ipsilesional modulation was initially found in stroke patients but not in the healthy controls. In the patient group, two evolutions were found in 6/8 patients: a significant increase in ipsilesional S_m; and a decreasing trend in contralesional S_m. In the only non-recovery patient, absence of ipsilesional modulation was observed, while his contralesional S_m increased with time after stroke.ConclusionThe two evolutions presumably reflect the reorganization of brain networks and functional recovery after acute stroke. The significant increase of ipsilesional S_m in patients with a good recovery suggests an important role of this hemisphere during recovery.SignificanceImproved understanding of ERD in acute stroke may assist in prognostication and rehabilitation.     

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.     

Event-related desynchronization during anticipatory attention for an upcoming stimulus: a comparative EEG/MEG study.

OBJECTIVES: Our neurophysiological model of anticipatory behaviour (e.g. Acta Psychol 101 (1999) 213; Bastiaansen et al., 1999a) predicts an activation of (primary) sensory cortex during anticipatory attention for an upcoming stimulus. In this paper we attempt to demonstrate this by means of event-related desynchronization (ERD). METHODS: Five subjects performed a time estimation task, and were informed about the quality of their time estimation by either visual or auditory stimuli providing Knowledge of Results (KR). EEG and MEG were recorded in separate sessions, and ERD was computed in the 8-10 and 10-12 Hz frequency bands for both datasets. RESULTS: Both in the EEG and the MEG we found an occipitally maximal ERD preceding the visual KR for all subjects. Preceding the auditory KR, no ERD was present in the EEG, whereas in the MEG we found an ERD over the temporal cortex in two of the 5 subjects. These subjects were also found to have higher levels of absolute power over temporal recording sites in the MEG than the other subjects, which we consider to be an indication of the presence of a 'tau' rhythm (e.g. Neurosci Lett 222 (1997) 111). CONCLUSIONS: It is concluded that the results are in line with the predictions of our neurophysiological model.     

Linear inverse source estimate of combined EEG and MEG data related to voluntary movements.

A method for the modeling of human movement-related cortical activity from combined electroencephalography (EEG) and magnetoencephalography (MEG) data is proposed. This method includes a subject's multi-compartment head model (scalp, skull, dura mater, cortex) constructed from magnetic resonance images, multi-dipole source model, and a regularized linear inverse source estimate based on boundary element mathematics. Linear inverse source estimates of cortical activity were regularized by taking into account the covariance of background EG and MEG sensor noise. EEG (121 sensors) and MEG (43 sensors) data were recorded in separate sessions whereas normal subjects executed voluntary right one-digit movements. Linear inverse source solution of EEG, MEG, and EEG-MEG data were quantitatively evaluated by using three performance indexes. The first two indexes (Dipole Localization Error [DLE] and Spatial Dispersion [SDis]) were used to compute the localization power for the source solutions obtained. Such indexes were based on the information provided by the column of the resolution matrix (i.e., impulse response). Ideal DLE values tend to zero (the source current was correctly retrieved by the procedure). In contrast, high DLE values suggest severe mislocalization in the source reconstruction. A high value of SDis at a source space point mean that such a source will be retrieved by a large area with the linear inverse source estimation. The remaining performance index assessed the quality of the source solution based on the information provided by the rows of the resolution matrix R, i.e., resolution kernels. The i-th resolution kernels of the matrix R describe how the estimation of the i-th source is distorted by the concomitant activity of all other sources. A statistically significant lower dipole localization error was observed and lower spatial dispersion in source solutions produced by combined EEG-MEG data than from EEG and MEG data considered separately (P < 0.05). These effects were not due to an increased number of sensors in the combined EEG-MEG solutions. They result from the independence of source information conveyed by the multimodal measurements. From a physiological point of view, the linear inverse source solution of EEG-MEG data suggested a contralaterally preponderant bilateral activation of primary sensorimotor cortex from the preparation to the execution of the movement. This activation was associated with that of the supplementary motor area. The activation of bilateral primary sensorimotor cortical areas was greater during the processing of afferent information related to the ongoing movement than in the preparation for the motor act. In conclusion, the linear inverse source estimate of combined MEG and EEG data improves the estimate of movement-related cortical activity.     

Event-related desynchronization in reaction time paradigms: a comparison with event-related potentials and corticospinal excitability.

OBJECTIVES: To study cortical activity in different motor tasks, we compared event-related desynchronization (ERD) and event-related potentials (ERPs) in different reaction time (RT) paradigms with the time course of corticospinal excitability. METHODS: Nine right-handed, normal subjects performed right or left thumb extensions in simple, choice and go/no go auditory RT paradigms. Eight subjects had participated in a previous study evaluating changes in corticospinal excitability during the same paradigms. Twenty-nine EEG channels with electrooculogram and bilateral EMG monitoring were collected. ERPs and ERD of 10 and 18-22 Hz bands were obtained with respect to tone administration and EMG onset. RESULTS: Trials with movement showed lateralized ERP components, corresponding to the motor potential (MP), both in the averages on the tone and on EMG. The MP corresponded well in time and location to the rise in corticospinal excitability on the moving side observed in the previous study. Sensorimotor ERD, followed by event-related synchronization (ERS), was present for trials with movements and for the no go. ERD was present contralaterally during movement preparation and in no go trials, while it was bilateral during motor execution. No go ERD was followed more rapidly by ERS than in trials with movement. This finding suggests that in no go trials, there is a brief active process in the sensorimotor areas. ERD and ERS do not correspond, respectively, in time and location to increases and decreases in corticospinal excitability. In fact, ERD is bilateral during movement execution, when corticospinal inhibition of the side at rest is observed. Contralateral no go ERS occurs later than corticospinal inhibition, which is bilateral. CONCLUSIONS: These findings may suggest that ERD is compatible with both corticospinal activation and inhibition, ERS indicating the removal of either, resulting in cortical idling.     

EEG sleep patterns in man: a twin study

All-night EEG sleep recording was performed for 3 consecutive nights in 26 pairs of normal male twins (14 monozygotic and 12 dizygotic) in order to investigate genetic components of sleep. The analysis was based on average values of repeated sleep measures and controlled for the effect of cohabitation. Our results indicate that a significant proportion of variance in stages 2, 4 and delta sleep as well as in REM density is genetically determined in man. Genetic influences on stage 1 and REM are strongly confounded by a synchronizing effect of the cohabitational status.     

Cerebral preparation of spontaneous movements: An EEG study

ObjectiveThe current study sought to determine whether there is a Bereitschaftspotential (BP) before uninstructed, spontaneous movements.Methods14 participants were seated on a comfortable armchair for one hour without any instruction except not to fall asleep and to keep their eyes open. Electroencephalography (EEG) and electromyography (EMG) activity were recorded during the whole session. EEG activity was analyzed before spontaneous movements and compared with EEG activity before repetitive, instructed movements in a separate session.ResultsBPs were identified in most participants with the spontaneous movements. The BPs with spontaneous movements were mostly localized in the medial frontocentral regions. The BPs with the instructed movements were localized primarily in the central regions and had larger amplitude.ConclusionPresence of a BP before movement does not depend on instruction and may be independent of conscious volition. The amplitude of the BP may depend on the amount of attention.SignificanceThis study shows that the presence of a BP before movement is not an “artifact” of the experimental instructions.     

Non-voluntary and voluntary processing of emotional prosody: an event-related potentials study

The present study investigated whether event-related potentials (ERPs) reflect non-voluntary vs voluntary processing of emotional prosody. ERPs were obtained while participants processed emotional information non-voluntarily (i.e. while evaluating semantic characteristics of a stimulus) and voluntarily (i.e. while evaluating emotional characteristics of a stimulus). Results suggest that emotional prosody is processed around 160 ms after stimulus onset under non-voluntary processing conditions (when the attention is diverted from the emotional meaning of the tone of voice); and around 360 ms under voluntary processing conditions. The findings support the notion that emotional prosody is processed non-voluntarily in the comprehension of a spoken message.     

EEG correlates of finger movements with different inertial load conditions as revealed by averaging techniques.

OBJECTIVE: The present study was aimed to further address the general empirical question regarding the sensitivity of EEG correlates toward specific kinematic and/or kinetic movement parameters. In particular, we examined whether adding different inertial loads to the index finger, while a subject produced various amplitudes of discrete finger movements, influenced the movement-related potentials (MRP). METHODS: Our experimental design systematically controlled the angular displacement, velocity and acceleration (kinematic) profiles of finger movement while torque (kinetics) was varied by adding different external loads opposing finger flexion movement. We applied time-domain averaging of EEG single trials in order to extract three movement-related potentials (BP-600 to -500 BP-100 to 0 and N0 to 100) preceding and accompanying 25, 50 and 75 degrees unilateral finger movements with no inertial load, small (100 g) and large (200 g) loading. RESULTS: It was shown that both inertial load and the degree of angular displacement of index finger flexion increased the amplitude of late components of MRP (BP-100 to 0 and N0 to 100) over frontal and precentral areas. In contrast, the external load and movement amplitude manipulations did not influence the earlier component of the MRP (BP- 600 to -500). CONCLUSIONS: Overall, the data demonstrate that adding inertial load to the finger with larger angular displacements involves systematic increase in activation across frontal and precentral areas that are related to movement initiation as reflected in BP-100 to 0 and N0 to 100.