DTI Tractography of the Human Brain’s language pathways.pdf

Cerebral Cortex doi:10.1093/cercor/bhn011 DTI Tractography of the Human Brain’s Language Pathways Matthew F. Glasser1 and James K. Rilling1,2,3,4 1Department of Anthropology, 2Department of Psychiatry and Behavioral Sciences, 3Center for Behavioral Neuroscience and 4Yerkes National Primate Research Center, Emory University, Atlanta, GA 30322, USA Diffusion Tensor Imaging (DTI) tractography has been used to detect leftward asymmetries in the arcuate fasciculus, a pathway that links temporal and inferior frontal language cortices. In this study, we more specifically define this asymmetry with respect to both anatomy and function. Twenty right-handed male subjects were scanned with DTI, and the arcuate fasciculus was reconstructed using deterministic tractography. The arcuate was divided into 2 segments with different hypothesized functions, one terminating in the posterior superior temporal gyrus (STG) and another terminating in the middle temporal gyrus (MTG). Tractog- raphy results were compared with peak activation coordinates from prior functional neuroimaging studies of phonology, lexical-- semantic processing, and prosodic processing to assign putative functions to these pathways. STG terminations were strongly left lateralized and overlapped with phonological activations in the left but not the right hemisphere, suggesting that only the left hemisphere phonological cortex is directly connected with the frontal lobe via the arcuate fasciculus. MTG terminations were also strongly left lateralized, overlapping with left lateralized lexical-- semantic activations. Smaller right hemisphere MTG terminations overlapped with right lateralized prosodic activations. We combine our findings with a recent model of brain language processing to explain 6 aphasia syndromes. Keywords: aphasia, arcuate fasciculus, asymmetry, lexical--semantic, phonologic, prosody Introduction Human language function was classically thought to be mediated by 2 brain areas in the left hemisphere: