Concordance of Language Lateralization Between Task Paradigms in Wernicke’s Area and Inferior Frontal Gyrus- an fMRI study

Studies have shown that when compared to more invasive methods, fMRI is an accurate predictor of language laterality by using blood flow changes in the brain as a surrogate indicator of brain activation. The determination of language dominance by fMRI is made possible by the use of language paradigms or tasks, which elicit signal changes in specific regions of the brain. Despite the aforementioned advancements in non-invasive language determination, what are lacking in the literature are studies aimed at identifying agreement between the various types of language tasks and language regions. In this study we compared four language tasks across two neuroanatomical regions of interest to analyze the concordance of language laterality between tasks in each region, as well as between regions during each task. Twenty-two right-handed healthy adult volunteers and seventy adult patients with partial epilepsy were scanned with a 3.0T General Electric between 2003 and 2015. Images were processed in SPM8. All subjects completed an auditory decision task (ADT), an auditory categorization task, a listening task and a reading task. Activation data were collected in the Inferior Frontal Gyrus (IFG) and Wernicke’s Area (WA), each selected based on their essential roles in language and the high levels of lateralization they have exhibited in previous fMRI studies. Language laterality was characterized in terms of a calculated laterality index (LI), as well as the categorical label left, right, or bilateral. As expected, patients showed the highest levels of atypical language dominance. However, for both controls and patients, the LI and categorical laterality data showed a strong tendency toward left-lateralization, with ADT proving to be the most lateralizing in both regions. For both groups, ADT was also the task with the most IFG-WA concordance (95% of controls and 80% of patients). WA was the most lateralized and most concordant region across all task pairs for both groups. Highest levels of IFG-WA concordance were observed across the Listen/Read task-pair in controls (100%) and the ADT/AUDCAT task-pair in patients (64%). Control subjects had significantly higher levels of complete agreement across all four tasks in WA than patients (68% vs. 33%). Control subjects also had significantly higher levels of complete agreement across all four tasks in IFG than patients (59% vs. 31%). Going forward, assessing concordance of lateralization of these language tasks in other brain regions will benefit our understanding of the greater language network and how its individual components drive language processes