The Arcuate Fasciculus: Analysis of White Matter Connection in Thai Language System Using Diffusion Tensor Imaging and Feasibility in Lateralization of the Dominant Hemisphere

Objective: The arcuate fasciculus (AF) is classically described as white matter connecting Broca’s and Wernicke’s area, which is important for language processing in human. In a previous study, lateralization of the AF to the left in normal healthy people was described. However, using the AF for lateralization of the dominant hemisphere in Thai speakers with Thai mother tongue language has not been studied. The purpose of this study was to demonstrate any feasibility that AF (by diffusion tensor imaging (DTI)) could be used to lateralize the dominant hemisphere in native-Thai speakers. Methods: Ten normal official Thai speakers with Thai mother tongue language (5 males, 5 females, mean age 24.9 years old; range 22-37 years old) were studied with DTI by 3T MRI using deterministic method in post processing software. The fractional anisotropy, relative fiber density index (RFD) and asymmetry index (AI) were analyzed to determine the dominant hemisphere. Comparison to functional hemispheric language lateralization from functional magnetic resonance imaging (fMRI) was done. Results: Slightly higher fractional anisotropy (FA) values for the left AF as compared with the right AF in all subjects were noted. The lateralization of RFD to the right were found in 5 subjects, to the left in 3 subjects and no definite lateralization in 2 subjects. The lateralization of AI to the right was found in 5 subjects, to the left in 3 subjects and no definite lateralization in 2 subjects. The lateralization from the fMRI language paradigm using visual analysis of all subjects were to the left. The anterior end of the AF tract was at par opercularis in 6, par triangularis in 3 and middle frontal gyrus in 5 subjects. The posterior end of the AF was at superior temporal gyrus in 7, middle temporal gurus in 9 and angular gyrus in 4 subjects. The area of termination of the AF was not correlated with activation from fMRI in 6 subjects when fused with word paradigm and in 7 subjects when fused with verb paradigm. Conclusion: The way to reconstruct the AF is feasible with practical method and software. However its clinical value to determine the dominant hemisphere in Thai subjects needs to be explored more with more advanced and promising technique.