Language in the brain at rest: new insights from resting state data and graph theoretical analysis

Abstract

In humans, the most obvious functional lateralization is the specialization of the left hemisphere for language. Therefore, the involvement of the right hemisphere in language is one of the most remarkable findings during the last two decades of fMRI research. However, the importance of this finding continues to be underestimated. We examined the interaction between the two hemispheres and also the role of the right hemisphere in language. From two seeds representing Broca's area, we conducted a seed correlation analysis (SCA) of resting state fMRI data and could identify a resting state network (RSN) overlapping to significant extent with a language network that was generated by an automated meta-analysis tool. To elucidate the relationship between the clusters of this RSN, we then performed graph theoretical analyses (GTA) using the same resting state dataset. We show that the right hemisphere is clearly involved in language. A modularity analysis revealed that the interaction between the two hemispheres is mediated by three partitions: A bilateral frontal partition consists of nodes representing the classical left sided language regions as well as two right-sided homologs. The second bilateral partition consists of nodes from the right frontal, the left inferior parietal cortex as well as of two nodes within the posterior cerebellum. The third partition is also bilateral and comprises five regions from the posterior midline parts of the brain to the temporal and frontal cortex, two of the nodes are prominent default mode nodes. The involvement of this last partition in a language relevant function is a novel finding.

Intrinsic functional organization of putative language networks in the brain following left cerebral hemispherectomy

“…Another region that tends to be recruited during language tasks in both neurotypical participants (Binder, 1997) and participants with hemispherectomy (Liégeois et al, 2008) is the middle temporal gyrus; however, exploratory analyses of functional connectivity of the middle temporal gyrus in control participants revealed a network that included several brain regions not specific to language function, so it was not considered further. We verified that the ICN obtained from our seed in the right IFG was indeed the putative language ICN by qualitatively comparing it with (a) the networks described in the literature (e.g., Muller & Meyer, 2014), (b) the Neurosynth map corresponding to the term “language” (Yarkoni et al, 2011), and (c) a language ICN in control participants, obtained by placing a seed ROI within the left IFG (MNI coordinates −53 20 15).…”

“…Within the RH, consistent patterns of connectivity were observed between the IFG and precentral gyrus, superior temporal sulcus, angular gyrus, temporal pole, left and, to a lesser extent, right cerebellum, and frontal pole. The analysis of the ICN obtained in neurotypical individuals demonstrated that the chosen ROI was effective at revealing the language network described in the previous studies (Muller & Meyer, 2014; Tie et al, 2014; Zhu et al, 2014). Thus, ROIs in the right IFG could be used as a starting point for exploring compensatory language networks in patients after hemispherectomy.…”

“…The clusters composing the network are listed in Table 2. Importantly, the ICN obtained by placing a seed in the right pars orbitalis included typical language regions, namely IFG, left angular gyrus, superior temporal sulcus, and clusters in both precentral gyri (Muller & Meyer, 2014). Within the RH, consistent patterns of connectivity were observed between the IFG and precentral gyrus, superior temporal sulcus, angular gyrus, temporal pole, left and, to a lesser extent, right cerebellum, and frontal pole.…”

“…According to the analysis by Muller and Meyer (Muller & Meyer, 2014), areas comprising the language network in the RH are not mirror images of their LH counterparts, although they do tend to be located within homologous structures, including inferior frontal gyrus, superior temporal sulcus, and precentral gyrus.…”

Mother’s voice and heartbeat sounds elicit auditory plasticity in the human brain before full gestation

“…Table 2. An alternative hypothesis to explain the bilateral plasticity in the AC in the present study can be supported by a growing body of research, suggesting that the apparent left-sided lateralization for speech and language processing, specifically in the AC, is not an absolute dominance but rather a shared expertise by the two hemispheres (79)(80)(81). The above hypotheses must be made with caution because at this premature age, cortical folding is still in flux and the majority of neurons are still migrating and have not yet reached their final cortical destination.…”