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Poster B63, Thursday, August 16, 3:05 – 4:50 pm, Room 2000AB

The superior longitudinal fasciculi or refining the fronto-parietal connectivity patterns between specific language regions

Elise B. Barbeau1,2,3, Denise Klein1,2,3, Michael Petrides1,2,3,4;1Cognitive Neuroscience Unit, Montreal Neurological Institute, McGill University, Montreal, 2Department of Neurology and Neurosurgery, McGill University, Montreal, 3Center for Research on Brain, Language and Music (CRBLM), Montreal, 4Department of Psychology, McGill University, Montreal

The Superior Longitudinal Fasciculus (SLF) connects the parietal cortex with language related cortical areas in ventrolateral frontal cortex. In standard reconstructions of language tracts with diffusion imaging tractography, the SLF is often mixed up with the arcuate fasciculus that connects the posterior temporal cortex with the frontal cortex. In macaque monkey gold standard tract tracing studies which involve the injection of radioactive tracers, the exact origin of the SLF in parietal cortical areas, the precise course of its axons and the exact termination in ventrolateral frontal areas has been established (Petrides and Pandya, 2009). This research demonstrated two distinct branches originating from the inferior parietal lobule: One branch (SLF II) links posterior parietal cortex (corresponding to the angular gyrus (ANG) in the human brain) with the frontal cortex (specifically BA 45), and another branch (SLF III) links the anterior part of the inferior parietal cortex (corresponding to the supramarginal gyrus (SMG)) with inferior frontal cortex (specifically BA 44). Our study aimed to use this critical information from experimental anatomical studies on macaque monkeys to reconstruct in vivo these two branches of SLF using diffusion tractography. We then used resting-state functional connectivity to support the distinct pattern of connectivity, and refine the connectivity within the parietal and frontal regions of interest. Thirty-seven right-handed healthy volunteers (mean age 24.5, range 18-34) were scanned with MRI (diffusion, anatomical and resting state). The diffusion MRI images were preprocessed using FSL and the tracts were reconstructed with Diffusion Toolkit and Trackvis using Regions of Interests (ROIs) drawn on the diffusion and coregistered anatomical scans. SPM conn toolbox was used to preprocess the resting state data as well as to perform whole brain ROI-to-Voxel and ROI-to-ROI second-level analyses. These two branches of the SLF could be reconstructed and clearly separated from the connections originating from the posterior temporal region, i.e. the arcuate fasciculus. The resting state analyses showed that the ANG was significantly more connected than the SMG to BA45 and the SMG showed more connectivity to BA 44, consistent with predictions from the macaque monkey data.

Topic Area: Methods