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Abstract
A classic left frontal-temporal brain network is known to support language processes. However, the level of participation of constituent regions, and the contribution of extra-canonical areas, is not fully understood; this is particularly true in children, and in individuals who have experienced early neurological insult. In the present work, we propose whole-brain connectivity and graph-theoretical analysis of magnetoencephalography (MEG) source estimates to provide robust maps of the pediatric expressive language network. We examined neuromagnetic data from a group of typically-developing young children (n = 15, ages 4–6 years) and adolescents (n = 14, 16–18 years) completing an auditory verb generation task in MEG. All source analyses were carried out using a linearly-constrained minimum-variance (LCMV) beamformer. Conventional differential analyses revealed significant (p < 0.05, corrected) low-beta (13–23 Hz) event related desynchrony (ERD) focused in the left inferior frontal region (Broca’s area) in both groups, consistent with previous studies. Connectivity analyses were carried out in broadband (3–30 Hz) on time-course estimates obtained at the voxel level. Patterns of connectivity were characterized by phase locking value (PLV), and network hubs identified through eigenvector centrality (EVC). Hub analysis revealed the importance of left perisylvian sites, i.e., Broca’s and Wernicke’s areas, across groups. The hemispheric distribution of frontal and temporal lobe EVC values was asymmetrical in most subjects; left dominant EVC was observed in 20% of young children, and 71% of adolescents. Interestingly, the adolescent group demonstrated increased critical sites in the right cerebellum, left inferior frontal gyrus (IFG) and left putamen. Here, we show that whole brain connectivity and network analysis can be used to map critical language sites in typical development; these methods may be useful for defining the margins of eloquent tissue in neurosurgical candidates.
Highlights
IntroductionNeuroimaging studies using functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) have consistently identified a left-lateralized frontal-temporal functional network for language processing in the vast majority of right-handed adults (∼95%; Binder et al, 1997; Gabrieli et al, 1998; Price, 2000; Hirata et al, 2004; Lohmann et al, 2010; Friederici, 2011, 2012; Kadis et al, 2011; Pei et al, 2011; Turken and Dronkers, 2011)
The pattern of hub distribution for degree and eigenvector centrality (EVC) were nearly identical; in contrast, the map derived from betweenness centrality was relatively focal to the left inferior frontal gyrus (IFG) (Figure 3)
Visual analyses suggested a better consistency for EVC with the connectivity patterns demonstrated on a subject-wise basis; EVC was preferred for subsequent analyses and interpretations
Summary
Neuroimaging studies using functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) have consistently identified a left-lateralized frontal-temporal functional network for language processing in the vast majority of right-handed adults (∼95%; Binder et al, 1997; Gabrieli et al, 1998; Price, 2000; Hirata et al, 2004; Lohmann et al, 2010; Friederici, 2011, 2012; Kadis et al, 2011; Pei et al, 2011; Turken and Dronkers, 2011). Involvement of subcortical structures in language processing has been supported by DCM for MEG and fMRI data related to auditory comprehension task (Booth et al, 2007; David et al, 2011). These studies have mainly focused on interactions of distinct nodal regions (seeds) or limited prespecified regions of interest (ROIs). The complexity of the brain network controlling language has remained largely unresolved with neuroimaging
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