Combined fMRI and DTI of the human low level visual cortex I. Abstract We study the anatomical connectivity network in the human low-level visual cortex using in vivo Magnetic Resonance Imaging techniques. 8 different visual areas were functionally mapped in each hemisphere of 4 subjects, and the white matter fibers network among them was then investigated using DTI. Various intra and inter-hemispheric connections were found, globally supporting the ventral/dorsal streams segregation. Keywords: fMRI, DTI, visual areas, retinotopy, functional mapping, Riemannian geometry, fiber tracking N. Wotawa †, C. Lenglet †, M. Roth *, B. Nazarian *, J.-L. Anton *, R. Majhoub *, R. Deriche †, O. Faugeras † (†) I.N.R.I.A., 2004 route des Lucioles, Sophia-Antipolis, France (*) Centre IRMf de Marseille, CHU Timone, Marseille, France Odyssée Lab V. Results and Conclusion III. ROIs definition from fMRI Two different criteria to define various low-level visual areas: retinotopy and functional selectivity Visual stimuli: 300x300 pixels video, 20.9°x20.9° visual angle, 72Hz refresh rate Attention and fixation controlled through a discrimination task at the fixation cross (normal: 0.5°, test: 0.77°) Preprocessings: Segmented areas: V1, V2v-V2d, V3v-V3d, V3A, V4. Volumetric ROIs computed through a 3mm “retro-projection” along the GM/WM interface normals 80°, 8 rotations 4 rotations 2/ Functional mapping of hMT+ (10mns) hMT+ complex: visual motion sensitive area, presumably human homologue of MT/V5 + MST (+ FST) Classical block design: RDP in coherent radial motion (7.53 deg.s -1, 2Hz alternating) VS flicker or static 2 x 5mns run, 3x8 blocks of ~17secs each hMT+ volumetric ROIs extracted with SPM99 - Marsbar Toolbox II. Data acquisition 3T MEDSPEC 30/80 AVANCE (Bruker) at the Centre IRMf de Marseille, quadrature bird-cage head coil Anatomical image: T1-weighted MPRAGE, TR=25msec, TE=5ms, FOV 256x230x180mm 3, voxel size = 1x0.75x1.22mm 3, 15mns fMRI: 30 pseudo-coronal slices, TR=2.111sec, TE=35ms, voxel size=2x2x2mm 3 DTI: 12 directions, repeated 8 times, b=1000 s.mm -2,  =38.5ms,  =21.6ms, TR=10000ms, TE=83ms. voxel size = 2x2x2mm 3, 20mns Investigation of the low level visual cortex areas considering 3 different characterization criteria within <1.5h of scans for the whole experiment Intra and Inter-hemispheric connexions were found in all subjects Good inter-subjects reproducibility (4 subjects) Our data support the dorsal (V1, V3A, hMT+) and v entral (V1, V2, V3, V4) streams 1462 W-PM Human Brain Mapping, Toronto, Ontario, Canada, June 12-16, / Retinotopic mapping of occipital areas (25mns) Standard procedure by phase-encoded stimulation of the visual field P-uncorr Centre IRMf Results of the fiber tracking with every white matter voxels taken as a seed from a single left hMT+ voxel. Dark values correspond to low mean along the fibers, indicating a strong connectivity index. White matter segmentation (Brainvisa and Absolut). Each white matter voxel is considered as a seed for the fiber tracking algorithm. IV. DTI Fiber Tracking & Connections Likelihood Basic idea: DTI fiber tracking and estimation of an index of connectivity for each fiber are conducted as follows. Diffusion tensor are used as a metric to first compute geodesic distances and then the shortest paths between the ROIs extracted from fMRI. A measure of likelihood for each computed fiber is then derived by looking at the minima of the distance function Euclidean gradient norm. Estimation of diffusion tensors by a robust gradient descent algorithm (see poster 736 T-PM) ROI Distance function computation: Statistics of along two distinct fibers toward the same target. Fibers with high variance (red) are discarded 3D rendering of geodesics with best statistical properties of with left hMT+ (red) as a target. Fiber tracts strongly connect contralateral hMT+ (green) and contralateral as well as ipsilateral (blue) V1 area. Synthetic example of distance function Real dataset distance function from a corpus callosum voxel over an axial slice  motion correction (INRIAlign Sofware)  cortical surface-based anisotropic smoothing, FWHM=3mm (Odyssee Lab. software)  MNI template normalization (SPM2)  Fiber with low confidence Mean = 1815 Standard deviation = 1160 Fiber with high confidence Mean = 1020 Standard deviation = 180