Dealing with mismatched fMRI activations in fMRI constrained EEG cortical source imaging: a simulation study assuming various mismatch types

Abstract

Although fMRI constrained EEG source imaging could be a promising approach to enhancing both spatial and temporal resolutions of independent fMRI and EEG analyses, it has been frequently reported that a hard fMRI constraint may cause severe distortion or elimination of significant EEG sources when there are distinct mismatches between fMRI activations and EEG sources. If estimating actual EEG source locations is important and fMRI prior information is used as an auxiliary tool to enhance the concentration of widespread EEG source distributions, it is reasonable to weaken the fMRI constraint when significantly mismatched sources exist. The present study demonstrates that the mismatch problem may be partially solved by extending the prior fMRI activation regions based on the conventional source imaging results. A hard fMRI constraint is then applied when there is no distinct mismatch, while a weakened fMRI constraint is applied when there are significant mismatches. A preliminary simulation study assuming different types of mismatches such as fMRI invisible, extra, and discrepancy sources demonstrated that this approach can be a promising option to treat mismatched fMRI activations in fMRI constrained EEG source imaging.

The Perception of Dynamic and Static Facial Expressions of Happiness and Disgust Investigated by ERPs and fMRI Constrained Source Analysis

“…Because of potentially mismatching generators in fMRI and EEG (for a detailed and critical discussion, see [26]), we seeded an fMRI-constrained source model, based on the results observed by Trautmann et al [27], complemented with additionally fitted regional sources (RSs) for the following reasons:…”

“…Second, several authors have stressed that source models can even be improved by additionally fitted sources because of possible mismatches between fMRI and EEG with regards to underlying activation patterns (see, e.g., [24], [26]). …”

“…Constraints have been shown to improve the validity of source models, reflected in higher rates of common variance explanation [23]–[25]. Moreover, they enhance the accuracy of seeded source models because spurious sources can largely be ruled out (see [26], for a more detailed methodological discussion of mismatched sources in EEG and fMRI).…”

“…In the present study, spatial BOLD-fMRI data from a prior study [27] applying the exact same experimental setup were used to improve the validity of respective combined seeded and extended source models, and to provide more insight into the spatio-temporal dynamics of perceptual emotional facial expression processing of realistic dynamic stimuli. Additionally, as mismatches between BOLD activation foci and EEG-sources have previously been reported [26], spatial information yielded in the prior fMRI-study by Trautmann et al [27] were complemented with additionally fitted sources.…”

“…In fact, underlying neural processing steps in neural sub-networks can be of transient and very fast nature. Hence, fMRI might have not detected the generators in posterior regions because the fMRI approach is rather related to brain activations integrated over time because of its low temporal resolution (for a more detailed discussion of these results, please refer to [26], [27]). …”