EEG Co-registration Research Articles

Direct lexical control of eye movements in Chinese reading: Evidence from the co-registration of EEG and eye tracking

The direct-lexical-control hypothesis stipulates that some aspect of a word’s processing determines the duration of the fixation on that word and/or the next. Although the direct lexical control is incorporated into most current models of eye-movement control in reading, the precise implementation varies and the assumptions of the hypothesis may not be feasible given that lexical processing must occur rapidly enough to influence fixation durations. Conclusive empirical evidence supporting this hypothesis is therefore lacking. In this article, we report the results of an eye-tracking experiment using the boundary paradigm in which native speakers of Chinese read sentences in which target words were either high- or low-frequency and preceded by a valid or invalid preview. Eye movements were co-registered with electroencephalography, allowing standard analyses of eye-movement measures, divergence point analyses of fixation-duration distributions, and fixated-related potentials on the target words. These analyses collectively provide strong behavioral and neural evidence of early lexical processing and thus strong support for the direct-lexical-control hypothesis. We discuss the implications of the findings for our understanding of how the hypothesis might be implemented, the neural systems that support skilled reading, and the nature of eye-movement control in the reading of Chinese versus alphabetic scripts.

Coregistration of EEG and eye-tracking in infants and developing populations.

Infants cannot be instructed where to look; therefore, infant researchers rely on observation of their participant's gaze to make inferences about their cognitive processes. They therefore started studying infant attention in the real world from early on. Developmental researchers were early adopters of methods combining observations of gaze and behaviour with electroencephalography (EEG) to study attention and other cognitive functions. However, the direct combination of eye-tracking methods and EEG to test infants is still rare, as it includes specific challenges. The current article reviews the development of co-registration research in infancy. It points out specific challenges of co-registration in infant research and suggests ways to overcome them. It ends with recommendations for implementing the co-registration of EEG and eye-tracking in infant research to maximise the benefits of the two measures and their combination and to orient on Open Science principles while doing so. In summary, this work shows that the co-registration of EEG and eye-tracking in infant research can be beneficial to studying natural and real-world behaviour despite its challenges.

Mu rhythm and corticospinal excitability capture two different frames of motor resonance: A TMS–EEG co-registration study

Humans are equipped with an extraordinary ability to understand and imitate actions by mapping the observed movement onto their own cortical motor system. Long-established lines of research have identified two correlates of this motor resonance following action observation: the mu rhythm event-related desynchronization (mu-ERD) recorded through electroencephalography (EEG) and the facilitation of motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) of the primary motor cortex (M1). Yet, whether mu-ERD and MEP facilitation reflect unique or distinct mechanisms is not conclusive, as prior work did not combine simultaneous TMS–EEG recording with a trial-by-trial analysis of the two markers. To address this issue, here, we used TMS–EEG co-registration while participants observed and executed finger movements. EEG was continuously recorded while single-pulse TMS was administered over the left M1 and MEPs were recorded from the right hand. We found stronger motor cortex recruitment during action execution and observation as shown by mu-ERD. MEPs instead were larger overall during action execution and showed a facilitation specific to the muscles involved in the observed movements. Interestingly, when analyzing these two parameters using a trial-by-trial statistical approach, we did not find any relationship between mu-ERD and MEPs within the action observation condition. Our findings support the notion that EEG and TMS indices of motor resonance reflect distinct neural mechanisms.

Age-related Changes in Cortical Excitability Linked to Decreased Attentional and Inhibitory Control

Understanding age-related changes in cortical excitability and their relation to cognitive functions will help to improve interventions based on non-invasive brain stimulation that aim to support cognitive function in older adults. Here, we investigate the relationship between cortical excitability, executive function, and underlying neural activity in samples of healthy young and older adults. These participants performed a Simon task during electroencephalogram (EEG) recording. During the task, participants had to respond to the colour of a lateralized stimulus while ignoring its spatial location. We studied event-related brain potential correlates of attentional and inhibitory control [i.e., the posterior contralateral negativity (N2pc) and central contralateral negativity (N2cc), respectively] related to the Simon task performance. We also used transcranial magnetic stimulation (TMS) EEG coregistration. In detail, we applied single-pulse TMS during EEG recording in order to analyse global mean field power (GMFP) and TMS-evoked potentials (TEPs) as correlates of cortical excitability. We found lower GMFP amplitude within 101–200 ms in older compared to young adults. Moreover, older adults showed smaller N45 amplitude and slower P180 latency. These findings suggest cortical excitability alterations related to ageing. Older adults also exhibited longer reaction times and N2pc and N2cc latencies, indicating that it took them longer to allocate attention to the target stimulus and inhibit the tendency to respond to the attended location. Finally, in older adults, cortical excitability alterations correlated with longer reaction times and N2pc latencies. These results suggest that age-related alterations in cortical excitability represent a dysfunctional change associated with physiological ageing.

TMS-EEG Co-Registration in Patients with Mild Cognitive Impairment, Alzheimer's Disease and Other Dementias: A Systematic Review.

An established method to assess effective brain connectivity is the combined use of transcranial magnetic stimulation with simultaneous electroencephalography (TMS–EEG) because TMS-induced cortical responses propagate to distant anatomically connected brain areas. Alzheimer’s disease (AD) and other dementias are associated with changes in brain networks and connectivity, but the underlying pathophysiology of these processes is poorly defined. We performed here a systematic review of the studies employing TMS–EEG co-registration in patients with dementias. TMS–EEG studies targeting the motor cortex have revealed a significantly reduced TMS-evoked P30 in AD patients in the temporo-parietal cortex ipsilateral to stimulation side as well as in the contralateral fronto-central area, and we have demonstrated a deep rearrangement of the sensorimotor system even in mild AD patients. TMS–EEG studies targeting other cortical areas showed alterations of effective dorsolateral prefrontal cortex connectivity as well as an inverse correlation between prefrontal-to-parietal connectivity and cognitive impairment. Moreover, TMS–EEG analysis showed a selective increase in precuneus neural activity. TMS–EEG co-registrations can also been used to investigate whether different drugs may affect cognitive functions in patients with dementias.

Cognitive brakes in interference resolution: A mouse-tracking and EEG co-registration study

Cognitive control is particularly challenged when it is necessary to resolve interference and correct our behavior on-the-fly. To do this, it is necessary to inhibit the ongoing wrong action and reprogram a new motor plan as appropriate for the current task. This ability requires a complex interaction between cognitive and motor control. Here, we aimed at shedding light on this interplay. To do this, we administered a spatial version of the Stroop task comprising blocks with different Proportion Congruency (PC) manipulations (i.e., manipulating the percentage of congruent trials at 25%, 50% or 75%), to elicit different cognitive control demands. Moreover, we used two techniques with high-temporal resolution, as we simultaneously recorded EEG and mouse trajectories, that can be considered the real-time kinematic correlates of the ongoing cognitive processing. Specifically, we analyzed the Event Related Potentials (ERPs) locked to the peak deceleration time, which marks the suppression of ongoing erroneous trajectories, and we estimated their neural sources. We found three PC-dependent ERP components engaging distinct neural regions, which showed a reduction of the Stroop effect for low-PC blocks. By using a novel co-registration of mouse-trajectories and EEG, we suggest that the observed components may reflect different mechanisms engaged by reactive cognitive control to resolve the interference, including the suppression of an ongoing but no longer appropriate response, the selection of the new motor plan and its actual updating.

MAGNETOENCEPHALOGRAPHY–ELECTROENCEPHALOGRAPHY CO-REGISTRATION USING 3D GENERALIZED HOUGH TRANSFORM

This study proposes an advanced co-registration method for an integrated high temporal resolution electroencephalography (EEG) and magnetoencephalography (MEG) data. The MEG has a higher accuracy for source localization techniques and spatial resolution by sensing magnetic fields generated by the entire brain using multichannel superconducting quantum interference devices, whereas EEG can record electrical activities from larger cortical surface to detect epilepsy. However, by integrating the two modality tools, we can accurately localize the epileptic activity compared to other non-invasive modalities. Integrating the two modality tools is challenging and important. This study proposes a new algorithm using an extended three-dimensional generalized Hough transform (3D GHT) to co-register the two modality data. The pre-process steps require the locations of EEG electrodes, MEG sensors, head-shape points of subjects and fiducial landmarks. The conventional GHT algorithm is a well-known method used for identifying or locating two 2D images. This study proposes a new co-registration method that extends the 2D GHT algorithm to a 3D GHT algorithm that can automatically co-register 3D image data. It is important to study the prospective brain source activity in bio-signal analysis. Furthermore, the study examines the registration accuracy evaluation by calculating the root mean square of the Euclidean distance of MEG–EEG co-registration data. Several experimental results are used to show that the proposed method for co-registering the two modality data is accurate and efficient. The results demonstrate that the proposed method is feasible, sufficiently automatic, and fast for investigating brain source images.

Predicting Alzheimer's disease severity by means of TMS–EEG coregistration

Clinical manifestations of Alzheimer's disease (AD) are associated with a breakdown in large-scale communication, such that AD may be considered as a “disconnection syndrome.” An established method to test effective connectivity is the combination of transcranial magnetic stimulation with electroencephalography (TMS–EEG) because the TMS-induced cortical response propagates to distant anatomically connected regions. To investigate whether prefrontal connectivity alterations may predict disease severity, we explored the relationship of dorsolateral prefrontal cortex connectivity (derived from TMS–EEG) with cognitive decline (measured with Mini Mental State Examination and a face–name association memory task) in 26 patients with AD. The amplitude of TMS–EEG evoked component P30, which was found to be generated in the right superior parietal cortex, predicted Mini Mental State Examination and face–name memory scores: higher P30 amplitudes predicted poorer cognitive and memory performances. The present results indicate that advancing disease severity might be associated with effective connectivity increase involving long-distance frontoparietal connections, which might represent a maladaptive pathogenic mechanism reflecting a damaged excitatory–inhibitory balance between anterior and posterior regions.

Prefrontal Modulation of Visual Processing and Sustained Attention in Aging, a tDCS-EEG Coregistration Approach.

The ability to sustain attention is integral to healthy cognition in aging. The right PFC (rPFC) is critical for maintaining high levels of attentional focus. Whether plasticity of this region can be harnessed to support sustained attention in older adults is unknown. We used transcranial direct current stimulation to increase cortical excitability of the rPFC, while monitoring behavioral and electrophysiological markers of sustained attention in older adults with suboptimal sustained attention capacity. During rPFC transcranial direct current stimulation, fewer lapses of attention occurred and electroencephalography signals of frontal engagement and early visual attention were enhanced. To further verify these results, we repeated the experiment in an independent cohort of cognitively typical older adults using a different sustained attention paradigm. Again, prefrontal stimulation was associated with fewer attentional lapses. These experiments suggest the rPFC can be manipulated in later years to increase top-down modulation over early sensory processing and improve sustained attention performance. This holds valuable information for the development of neurorehabilitation protocols to ameliorate age-related deficits in this capacity.

Short latency intracortical inhibition in the angular gyrus characterized by paired-pulse TMS and EEG co-registration

Short latency intracortical inhibition in the angular gyrus characterized by paired-pulse TMS and EEG co-registration

Combination of Electroencephalography and Near-Infrared Spectroscopy in Evaluation of Mental Concentration during the Mental Focus Task for Wisconsin Card Sorting Test

Near-infrared spectroscopy (NIRS) is a noninvasive neuroimaging tool for measuring evoked functional changes in brain oxygenation. Electroencephalography (EEG) can be used to evaluate the functionality of cortical connections and obtain information on regional cortical activity. Coregistration of EEG–NIRS is a recent technique that has been applied for measuring changes in electrical and hemodynamic activity in the human brain. EEG–NIRS coregistration facilitates the avoidance of misleading interpretations of NIRS, particularly in the diagnosis of neurological disorders. In this study, we investigated an approach for enhancing accuracy of NIRS by using EEG to monitor physiological activity during a mental focus task. Using the Wisconsin Card Sorting Test for the subjects mental focus task, we identified two trend types in the EEG and NIRS signals of normal subjects. These data can assist in understanding brain activation statuses and enable determining subjects’ degree of mental concentration. If the data can be standardized for the diagnosis of neurological disorders, they can provide a new index to improve traditional methods (e.g., questionnaires) to assist clinical doctors in diagnosing cognitive disorders.

Combining EEG and eye movement recording in free viewing: Pitfalls and possibilities

Co-registration of EEG and eye movement has promise for investigating perceptual processes in free viewing conditions, provided certain methodological challenges can be addressed. Most of these arise from the self-paced character of eye movements in free viewing conditions. Successive eye movements occur within short time intervals. Their evoked activity is likely to distort the EEG signal during fixation. Due to the non-uniform distribution of fixation durations, these distortions are systematic, survive across-trials averaging, and can become a source of confounding. We illustrate this problem with effects of sequential eye movements on the evoked potentials and time-frequency components of EEG and propose a solution based on matching of eye movement characteristics between experimental conditions. The proposal leads to a discussion of which eye movement characteristics are to be matched, depending on the EEG activity of interest. We also compare segmentation of EEG into saccade-related epochs relative to saccade and fixation onsets and discuss the problem of baseline selection and its solution. Further recommendations are given for implementing EEG-eye movement co-registration in free viewing conditions. By resolving some of the methodological problems involved, we aim to facilitate the transition from the traditional stimulus-response paradigm to the study of visual perception in more naturalistic conditions.

Time course of the P300 Eye-Fixation Related Potential during the visual search for a target embedded in natural scenes

The Event Related Potential P300 has been intensively studied for over forty years (Polish, 2012). It is elicited at each updating of the stimulus representation, reflecting a cascade of cognitive processes engaging attentional and memory mechanisms. This potential is a positive component, appearing 300ms after stimulus onset, with maximal amplitude in centro-parietal regions. This study is mainly concerned by the analysis of the appearance and evolution of the P300 elicited by the onset of successive fixations recorded during a visual search using an ecological experimental paradigm. This goal is achieved through the co-registration of electroencephalographic (EEG) and eye-tracking (ET) signals. EEG and ET signals were recorded for thirty-four observers when exploring natural scenes during 5 sec to answer if a target object was or not present. To solve the main difficulty due to overlaps between the observed Eye Fixation Related Potentials (EFRP) elicited by consecutive fixations, we have used a new methodology based on the xDawn algorithm (Rivet, et al.; 2009). From each trial, a temporal window of 2s centered on the first fixation inside the Region of Interest (target). This duration was chosen to include five consecutive fixations (two before the first entrance, and two after). The fixations were tagged depending to their rank and position (inside/outside) the ROI. Neural activities were modelled as a cumulative response of specific latent responses elicited by each fixation with the corresponding onset. After xDawn estimation, the topographic maps have shown a potential identified as the P300 component elicited by the visual input through the consecutive fixations landed on the ROI. This result confirms previous studies but has been obtained for the first time on ecological paradigm thanks to the co-registration of EEG and ET signals and a new methodology to denoise potentials from overlaps of potentials elicited by consecutive fixations. Meeting abstract presented at VSS 2015

Safety of EEG–fMRI recordings in newborn infants at 3T: A study using a baby-size phantom

ObjectiveWe aimed to study EEG electrode temperatures during MRI recordings using a neonatal-size phantom to establish the safety of neonatal EEG–MRI. MethodsWe constructed a phantom set-up for co-registration of EEG and MRI measurements with newborn size configurations. The set-up consisted of a spherical glass phantom fitted with a customised MRI-compatible 64-channel EEG cap and EEG amplifier. Temperatures were recorded during and after five different scanning sequences (two T2∗ sensitised BOLD fMRI, one T1-weighted and two T2-weighted spin echo) in five electrode locations using a thermistor that was integrated into the electrode housing. A temperature increase >4°C was defined a priori as the safety limit. ResultsDuring fMRI and T1 sequences, none of the electrodes showed meaningful temperature changes. Only one MRI sequence (T2 with Max turbo factor 25; SAR 89%) caused temperature increase in one electrode (Fpz; +4.1°C) that slightly exceeded our predefined safety limit, while the conventional T2 sequence was within safety limits (up to +1.7°C). ConclusionsCo-registration of EEG and fMRI can be considered safe in babies with respect to electrode heating, which is the primary safety concern. SignificanceThe present findings open up a possibility to commence studies where EEG and MRI/fMRI are co-registered in human babies. Such studies hold significant promise of a better understanding of the early development of brain function and neurovascular coupling.

P 158. Neural correlates of Hebbian and anti-hebbian spike-timing-dependent plasticity in human: A TMS–EEG combined study

Introduction In a recent work by our group we used transcranial magnetic stimulation (TMS) to repeatedly activate the connection between the posterior parietal cortex (PPC) and the primary motor cortex (M1) of the left dominant hemisphere with a paired associative stimulation (PAS) protocol. By varying inter-pulse interval and the activation of different M1 neuronal populations we were able to induce LTP or LTD-like effects as indexed by Motor Evoked Potentials (MEPs) amplitude modulation that followed either Hebbian or anti-Hebbian temporal rules. Objectives Our aim was to further investigate the effects induced by this cortico-cortical PAS protocol over EEG activity, by means of a TMS–EEG coregistration approach. Materials and methods 13 volunteers underwent our novel PAS protocol. Paired stimuli were applied with PPC-TMS preceding (+5 ms) or following (−5 ms) M1 stimulation. In a third condition, the induced current direction over M1 was changed from postero–anterior (PA) to antero–posterior (AP) and the ISI was set at +5 ms. Eighty single pulse TMS were applied to M1 before and after PAS while continuously acquiring EEG from 21 electrodes and recording MEPs from the first dorsal interosseous muscle. We then analysed (i) functional coupling though event-related coherence (ERcoh) for alpha (8–12 Hz) and beta (13–30 Hz) band, (ii) changes in M1 reactivity through TMS-Evoked Potentials (TEPs) and (iii) MEPs amplitude. Results When PPC preceded M1PA stimulation (+5 ms) MEPs amplitude significantly decreased ( p = 0.001), while there was a concurrent increase in ERcoh for the beta band, topographically restricted to P3–C3 pair ( p = 0.02), representing the closest electrodes to the stimulated regions. TEPs analysis indicated a decrease of those components forming a dipole over left centro-parietal sites peaking at about 13 and 20 ms. When PPC followed M1PA stimulation (−5 ms) an increase in MEPs amplitude was induced (p = 0.01) with a concurrent ERcoh increase in the alpha band for P3–C3 pair ( p = 0.01). TEPs component were again modulated at 13 and 20 ms, with an increased amplitude after PAS administration. The AP condition led to opposite results: an increased MEP amplitude when PPC preceded M1AP stimulation (p). Conclusions These findings shed new light on the cortical mechanisms underlying antithetic learning rules in humans. We found that both post-synaptic long term potentiation or depression are always associated to an increased functional connectivity that exclusively upsurge between the stimulated areas. However, the sign of cortical plasticity in M1 is indexed by different brain oscillation activities in the alpha and beta bands. Finally distinct plastic changes differently modulate M1 reactivity as indexed by opposite changes of TEPs amplitude.

Artifact removal in co-registered EEG/fMRI by selective average subtraction

Objective Co-registration of EEG (electroencephalogram) and fMRI (functional magnetic resonance imaging) remains a challenge due to the large artifacts induced on the EEG by the MR (magnetic resonance) sequence magnetic fields. Thus, we present an algorithm, based on the average-subtraction method, which is able to correct EEG data for gradient and pulse artifacts. Methods MR sequence timing parameters are estimated from the EEG data and both slice and volume artifact templates are subtracted from the data. A clustering algorithm is proposed to account for the variability of the pulse artifact. Results The algorithm is able to keep the spontaneous EEG as well as visual evoked potentials (VEPs), while removing gradient and pulse artifacts with only a subtraction of selectively averaged data. In the frequency domain, the artifact frequencies are strongly attenuated. Estimated MR sequence time parameters showed that the correction is extremely sensitive to the slice time value. Pulse artifact clustering showed that most of the variability is due to the time jitter of the pulse artifact markers. Conclusions Selective subtraction of averages in combination with proper time alignment is enough to remove most of the MR-induced artifacts. Significance Clean EEG can be obtained from raw signals that are corrupted by MR-induced artifacts during simultaneous EEG–fMRI scanning without using dedicated hardware to synchronize EEG and fMRI clocks.

Magnetoencephalographic spikes not detected by conventional electroencephalography

Objective: To investigate some of the reasons why magnetoencephalographic (MEG) spikes are at times not apparent in conventional electroencephalograms (EEG) when the data are co-registered, and to explore to what extent modern EEG analysis methods can improve the yield. Methods: Seventy seconds of MEG–EEG co-registration on a 122 channel Neuromag system were studied in a 10-year-old boy with Landau–Kleffner syndrome. Twenty-six EEG channels were originally recorded with a left ear reference. The EEG data were subsequently reformatted (BESA) to a variety of montages for the 10–20 and 10–10 electrode array. A 10 s data epoch was compared in detail for concordance between MEG and EEG spikes. To detect the characteristics of hidden low voltage EEG spikes, MEG spikes were averaged and compared with the concomitant averaged EEG spike. Results: While there was an abundance of EEG as well as MEG spikes on the left; definite right-sided spikes were not visible in the EEG. Right hemispheric MEG spikes were, however, plentiful with an average strength of 757 fT. When the individual MEG spikes from the right hemisphere were compared with the corresponding EEG events their amplitude ranged between 24 and 31 μV and were, therefore, indistinguishable from background activity. The majority of them became visible, however, with further sophisticated data analysis. Conclusions: When the relative merits of MEG versus EEG recordings for the detection of epileptogenic spike are investigated the 10–20 system of electrode placement and conventional methods of EEG analysis do not provide optimal data assessment. The use of the 10–10 electrode array combined with modern methods of digital data analysis can provide better concordance with MEG data.

Co-registration of EEG and MRI data using matching of spline interpolated and MRI-segmented reconstructions of the scalp surface.

Accurate co-registration of MRI and EEG data is indispensable for the correct interpretation of EEG maps or source localizations in relation to brain anatomy derived from MRI. In this study, a method for the co-registration of EEG and MRI data is presented. The method consists of an iterative matching of EEG-electrode based reconstructions of the scalp surface to scalp-segmented MRIs. EEG-electrode based surface reconstruction is achieved via spline interpolation of individually digitized 3D-electrode coordinates. In contrast to other approaches, neither fiducial determination nor any additional provisions (such as bite bars, other co-registration devices or head shape digitization) are required, and co-registration errors associated with inaccurate fiducial determination are avoided. The accuracy of the method was estimated by calculating the root-mean-square (RMS) deviation of spline interpolated and MRI-segmented surface reconstructions in 20 subjects. In addition, the distance between co-registered and genuine electrode coordinates was assessed via a simulation study, in which surface reconstruction was based on virtual electrodes determined on the scalp surface of a high-resolution MRI data set. The mean RMS deviation of surface reconstructions was 2.43 mm, and the maximal distance between any two matched surface points was 5.06 mm. The simulated co-registration revealed a mean deviation of genuine and co-registered electrode coordinates of 0.61 mm. It is concluded that surface matching using spline interpolated reconstructions of scalp surfaces is a precise and highly practicable method to co-register EEG and MRI data.

On the relationship of synaptic activity to macroscopic measurements: does co-registration of EEG with fMRI make sense?

A two-scale theoretical description outlines relationships between brain current sources and the resulting extracranial electric field, recorded as EEG. Finding unknown sources of EEG, the so-called "inverse problem", is discussed in general terms, with emphasis on the fundamental non-uniqueness of inverse solutions. Hemodynamic signatures, measured with fMRI, are expressed as voxel integrals to facilitate comparisons with EEG. Two generally distinct cell groups (1 and 2), generating EEG and fMRI signals respectively, are embedded within the much broader class of synaptic action fields. Cell groups 1 and 2 may or may not overlap in specific experiments. Implications of this incomplete overlap for co-registration studies are considered. Each experimental measure of brain function is generally sensitive to a different kind of source activity and to different spatial and temporal scales. Failure to appreciate such distinctions can exacerbate conflicting views of brain function that emphasize either global integration or functional localization.

363 Probability patterns of the narrowband EEG subtraction spectra in humans during memory and storage performance

Co-registration of EEG (electroencephalogram) and fMRI (functional magnetic resonance imaging) remains a challenge due to the large artifacts induced on the EEG by the MR (magnetic resonance) sequence magnetic fields. Thus, we present an algorithm, based on the average-subtraction method, which is able to correct EEG data for gradient and pulse artifacts.MR sequence timing parameters are estimated from the EEG data and both slice and volume artifact templates are subtracted from the data. A clustering algorithm is proposed to account for the variability of the pulse artifact.The algorithm is able to keep the spontaneous EEG as well as visual evoked potentials (VEPs), while removing gradient and pulse artifacts with only a subtraction of selectively averaged data. In the frequency domain, the artifact frequencies are strongly attenuated. Estimated MR sequence time parameters showed that the correction is extremely sensitive to the slice time value. Pulse artifact clustering showed that most of the variability is due to the time jitter of the pulse artifact markers.Selective subtraction of averages in combination with proper time alignment is enough to remove most of the MR-induced artifacts.Clean EEG can be obtained from raw signals that are corrupted by MR-induced artifacts during simultaneous EEG–fMRI scanning without using dedicated hardware to synchronize EEG and fMRI clocks.