Increased inter-hemispheric functional connectivity for concrete word imagery compared to abstract word imagery

Many behavioral and neuroimaging studies have shown that the human brain represents, recall and learn concrete words more accurately and easier than abstract words. This phenomenon is defined as the concreteness effect. Dual coding theory is one of the main important theories which is often used to justify the concreteness effect. Several neuroimaging studies tried to localize and compare activated areas during concrete and abstract word processing, but brain connectivity was not studied in the above tasks. In a fMRI experiment, we acquired fMRI data from 11 healthy volunteers in the visual mental imagery of concrete and abstract characteristics. In a novel work, we then used inter-hemispheric connectivity to compare the brain hemispheres integration between concrete and abstract word processing. Twelve important brain regions reported in previous studies of abstract or concrete concept processing were selected. Then the correlations of BOLD activity of each region with its corresponding contralateral region were calculated and compared for the time intervals of concrete and abstract word processing. Results revealed that the inter-hemispheric connectivity during concrete word imagery was significantly different compared to abstract word imagery (FDR correction, q = 0.05) in three contrasting regions which were middle occipital gyrus, inferior occipital gyrus and temporal pole (superior temporal gyrus). Notably, in all of these three areas, the inter-hemispheric functional connectivity was significantly stronger during concrete word imagery to that of abstract. These results imply that the synchronization between brain hemispheres within visual and language processing areas is significantly stronger for imagery of concrete words (more imageable words) than that of abstract words (less imageable words).