FALCON: a Functional Atlas of Language COmprehension Networks based on multiple task-induced activation mapping and graph analysis of intrinsic connectivity in 137 healthy right-handers

Abstract

We herein propose an atlas of 32 language-related areas based on a 3-step method combining the analysis of activation and asymmetry during multiple language tasks with hierarchical clustering of resting-state connectivity and graph analyses. In total, 144 healthy right-handers performed fMRI runs based on language production, reading and listening, both with sentences and lists of over-learned words. Sentence minus word-list BOLD contrast and left-minus-right BOLD asymmetry for each language task were computed in pairs of homotopic regions of interest (hROIs) from the AICHA atlas. Thirty-two hROIs were identified that were conjointly activated and leftward asymmetrical in each of the 3 language contrasts. Analysis of resting-state temporal correlations of BOLD variations between these 32 hROIs allowed the segregation of four networks: LANG_CORE (including 16 hROIs of language-essential areas), LANG_EXE (including 4 hROIs involved in executive functions), LANG_VISU (composed of 5 hROIs belonging to visual cortices), and LANG_DMN (including 7 hROIs belonging to the default mode network (DMN)). At rest, LANG_CORE was positively correlated with LANG_EXE and negatively correlated with LANG_DMN. Graph analysis methods applied to LANG_CORE hROIs revealed that the pars triangularis region of the inferior frontal gyrus and 2 hROIs of the superior temporal sulcus were hubs based on their degree centrality (DC), betweenness and participation values. These core areas for intra- and inter-network communication correspond to the epicentres of sentence processing. Positive correlations between DC and BOLD activation strength values were observed in not only LANG_CORE hROIs across individuals but also across regions regardless of the language task, demonstrating that more connected areas have stronger activation responses. DC measurements in LAN_CORE may thus be a valuable index to evaluate inter-individual variations in language area activities in large populations in relation to anatomical and clinical patterns in language pathologies. The atlas comprising these 4 networks is named FALCON (Functional Atlas of Language COmprehension Networks) and can be downloaded at http://www.gin.cnrs.fr/en/tools/.