title: Spurious correlations in simultaneous EEG-fMRI driven by in-scanner movement.
abstract: Simultaneous EEG-fMRI provides an increasingly attractive research tool to investigate cognitive processes with high temporal and spatial resolution. However, artifacts in EEG data introduced by the MR scanner still remain a major obstacle. This study, employing commonly used artifact correction steps, shows that head motion, one overlooked major source of artifacts in EEG-fMRI data, can cause plausible EEG effects and EEG-BOLD correlations. Specifically, low-frequency EEG (<20Hz) is strongly correlated with in-scanner movement. Accordingly, minor head motion (<0.2mm) induces spurious effects in a twofold manner: Small differences in task-correlated motion elicit spurious low-frequency effects, and, as motion concurrently influences fMRI data, EEG-BOLD correlations closely match motion-fMRI correlations. We demonstrate these effects in a memory encoding experiment showing that obtained theta power (~3-7Hz) effects and channel-level theta-BOLD correlations reflect motion in the scanner. These findings highlight an important caveat that needs to be addressed by future EEG-fMRI studies.
authors.affiliation: Fachbereich Psychologie, Universität Konstanz, Postfach 905, 78457 Konstanz, Germany; Department of Neuropsychology, Institute of Cognitive Neuroscience, Ruhr University Bochum, 44801 Bochum, Germany. Electronic address: marie-christin.fellner@rub.de.
authors.forename: M-C
authors.initials: MC
authors.lastname: Fellner
authors.affiliation: Universität Regensburg, Psychologie, 93040 Regensburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Volberg
authors.affiliation: University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom; Sir Peter Mansfield Magnetic Resonance Centre, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: K J
authors.initials: KJ
authors.lastname: Mullinger
authors.affiliation: Universität Regensburg, Psychologie, 93040 Regensburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Goldhacker
authors.affiliation: University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Wimber
authors.affiliation: Universität Regensburg, Psychologie, 93040 Regensburg, Germany.
authors.forename: M W
authors.initials: MW
authors.lastname: Greenlee
authors.affiliation: Fachbereich Psychologie, Universität Konstanz, Postfach 905, 78457 Konstanz, Germany; University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Hanslmayr
mesh_terms: D000328:Adult; D016477:Artifacts; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography; D005260:Female; D019416:Head Movements; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology*; D009038:Motion; D009415:Nerve Net / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D013826:Theta Rhythm / Q000502:physiology
keywords: EEG–BOLD correlations; Motion artifacts; Simultaneous EEG-fMRI; Subsequent memory effect; Theta oscillations