Abstract
Simultaneous registration of scalp electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) is considered an attractive approach for studying brain function non-invasively. It combines the better spatial resolution of fMRI with the better temporal resolution of EEG, but comes at the cost of increased measurement artifact and the accompanying artifact preprocessing. This paper presents a study of the residual signal quality based on temporal signal to noise ratio (TSNR) for fMRI and fast Fourier transform (FFT) for EEG, after optimized conventional signal preprocessing. Measurements outside the magnetic resonance imaging scanner and inside the scanner prior to and during image acquisition were compared. For EEG, frequency and region dependent significant effects on FFT squared amplitudes were observed between separately vs. simultaneously recorded EEG and fMRI, with larger effects during image acquisition than without image acquisition inside the scanner bore. A graphical user interface was developed to aid in quality checking these measurements. For fMRI, separately recorded EEG-fMRI revealed relatively large areas with a significantly higher TSNR in right occipital and parietal regions and in the cingulum, compared to separately recorded EEG-fMRI. Simultaneously recorded EEG-fMRI showed significantly higher TSNR in inferior occipital cortex, diencephalon and brainstem, compared to separately recorded EEG-fMRI. Quantification of EEG and fMRI signals showed significant, but sometimes subtle, changes between separate compared to simultaneous EEG-fMRI measurements. To avoid interference with the experiment of interest in a simultaneous EEG-fMRI measurement, it seems warranted to perform a quantitative evaluation to ensure that there are no such uncorrectable effects present in regions or frequencies that are of special interest to the research question at hand.
Highlights
Simultaneous registration of scalp EEG and functional magnetic resonance imaging (fMRI) is considered an attractive approach for studying brain function non-invasively, because it combines the better spatial resolution of fMRI with the better temporal resolution of EEG (Laufs, 2012; Jorge et al, 2014; Murta et al, 2015; Abreu et al, 2018)
Index of dispersion analysis of A2(f ), the squared amplitude of fast Fourier transform (FFT), showed no significant differences at the FDRcorrected p < 0.05 between the [EEG][fMRI] and [EEG fMRI] recording conditions it was systematically higher in the simultaneous measurement ([EEG fMRI]) compared to the separate recording condition
For example comparing spectral differences between EEG measured inside the scanner with and without image acquisition during periodic fMRI recordings (Allen et al, 2000; Laufs et al, 2003; Ritter et al, 2007), and EEG measured inside the scanner during image acquisition and outside the scanner (Allen et al, 1998; Bénar et al, 2003)
Summary
Simultaneous registration of scalp EEG and fMRI is considered an attractive approach for studying brain function non-invasively, because it combines the better spatial resolution of fMRI with the better temporal resolution of EEG (Laufs, 2012; Jorge et al, 2014; Murta et al, 2015; Abreu et al, 2018).The EEG and fMRI signal sources are different. Simultaneous registration is especially useful for the analysis of single trial correlations between the fMRI and EEG signal (Jorge et al, 2015). The validity of this combined approach relies on the tight coupling of the hemodynamic and electrophysiological responses in selected conditions (Huster et al, 2012). It has been successfully used in several fields of fundamental research (e.g., Mijovicet al., 2012) as well as in clinical practice (e.g., Tousseyn et al, 2014). Simultaneous registration does come at the cost of increased measurement artifact and the accompanying artifact preprocessing, especially for EEG (Huster et al, 2012)
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