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Have you tried replicating the tractography method of Zorei et al in your data just to see what you get? You should be able to find any significant pathway with 5000 samples, although 25000 may give more precision, especially in cases where the 2nd fiber direction comes into play. I don't think you should expect significant interhemispheric connectivity in all human brain regions, given the amount of hemispheric specialization in humans (relative to other primates). Peace, Matt. -----Original Message----- From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf Of Cherif Sahyoun Sent: Sunday, November 02, 2008 9:36 PM To: [log in to unmask] Subject: Re: [FSL] interhemispheric tracking Hi Matt, Funny, I was just downloading your new cerebral cortex paper! I've tried a couple of different pathways, all from white matter 2.5mm in from functional maps. One example is from the left to the right white matter adjacent to the intraparietal sulcus. With seeds in the CC, Zorei et al. found good connectivity to the posterior parietal, but maybe I need more samples (I'm using 5000) if intra-hemispheric connections are much more likely than inter-hemispheric ones and causing me to "run out of samples" before I exhaust possibilities? I don't think it's a diffusion lines issue, as I've successfully run pathways within hemispheres in the same datasets, and the V1 files look fine in fslview. Thanks, Cherif ---------------------------------------------------------------------------- -------------- Cherif P. Sahyoun HST-MEMP Developmental Neuroimaging of Cognitive Functions C: 617 688 8048 H: 617 424 6956 [log in to unmask] "Live as if this were your last day. Learn as if you'll live forever" Ghandi ---------------------------------------------------------------------------- --------------- On Sun, Nov 2, 2008 at 11:15 PM, Matt Glasser <[log in to unmask]> wrote: > What regions are you trying to track between? Have you verified that your > diffusion lines are properly oriented? > > Peace, > > Matt. > > -----Original Message----- > From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf > Of Cherif Sahyoun > Sent: Sunday, November 02, 2008 9:13 PM > To: [log in to unmask] > Subject: [FSL] interhemispheric tracking > > Hi, > > I am finding difficulties running probtrackx with a seed mask in one > hemisphere and a waypoint in the other. In most subjects, the pathway does > not "find its way" across. > I am using a hemispheric mask with a decently sized "window" around the > corpus callosum to allow passage of samples. > > Has anyone experienced similar difficulties? I seem to remember a casual > conversation about this being a common shortcoming of any tractography > method, but don't know if it was ever rationalized... > > Thanks in advance, > Cherif >