Concordance of MEG and fMRI patterns in adolescents during verb generation

Abstract

In this study we focused on direct comparison between the spatial distributions of activation detected by functional magnetic resonance imaging (fMRI) and localization of sources detected by magnetoencephalography (MEG) during identical language tasks. We examined the spatial concordance between MEG and fMRI results in 16 adolescents performing a three-phase verb generation task that involves repeating the auditorily presented concrete noun and generating verbs either overtly or covertly in response to the auditorily presented noun. MEG analysis was completed using a synthetic aperture magnetometry (SAM) technique, while the fMRI data were analyzed using the general linear model approach with random-effects. To quantify the agreement between the two modalities, we implemented voxel-wise concordance correlation coefficient (CCC) and identified the left inferior frontal gyrus and the bilateral motor cortex with high CCC values. At the group level, MEG and fMRI data showed spatial convergence in the left inferior frontal gyrus for covert or overt generation versus overt repetition, and the bilateral motor cortex when overt generation versus covert generation. These findings demonstrate the utility of the CCC as a quantitative measure of spatial convergence between two neuroimaging techniques.

Fig. 1

Timing diagram of the event-related verb-generation for MEG and fMRI task. MEG: 30 5-s Trials for each condition are recorded. FMRI: 15 36-s cycles for each phase of the paradigm are presented for a total scan time of 9 min. Overt verb generation performance is recorded for both MEG and fMRI sessions.

Fig. 2

Group composite activation maps of three contrasts from MEG (left) and fMRI (right) results (N=16): (C1) Say > Repeat (covert generation versus overt repetition); (C2) Think > Repeat (overt generation versus overt repetition); (C3) Say > Think (overt generation versus covert generation). Significant level for all contrasts: p<0.05 corrected. Cluster size > 15. Slice range: Z=–8 to +47 mm (Talairach coordinates) and 5 mm between each successive slice displayed. All images are in radiologic orientation.

Fig. 3

CCC maps of three contrasts. (C1) Say > Repeat (covert generation versus overt repetition); (C2) Think > Repeat (overt generation versus overt repetition); (C3) Say > Think (overt generation versus covert generation). Thresholded at 0.3. Cluster size > 10. Slice range: Z=–8 to +47 mm (Talairach coordinates) and 5 mm between each successive slice displayed. All images are in radiologic orientation.