since the tractgraphy is ran in the individual's difussin space, a subject with big striatum and big hippocampus will show stronger connectivity between striatum and hippocampus than that of small striatum and small hippocampus. I want to know if the local brain volume(no matter gray or white matter) affects the fiber connectivity between two regions.

Xuemei

On Thu, Sep 27, 2012 at 11:08 PM, Saad Jbabdi <[log in to unmask]> wrote:

Hi - Not sure exactly what you're asking. probtrackx does the same thing whether it's in GM or WM: It samples from the uncertainty distribution. Generally, this distribution is wider, sometimes almost uniform, in GM than WM. If for some reason some subjects have different uncertainty distributions (or orientations) than others, then this will be reflected as differences in the trajectory distribution.

Cheers
Saad

On 27 Sep 2012, at 12:56, xuemei lei wrote:

Hi all,
The probabilistic tracking was ran from the seed striatum to nine target regions via the probtrackX, and produced nine images, each for one target region showing the fiber connectivity between the seed striatum and the target region.

However reviewers raised a question: is there a potential confound that if the local gray matter structure is different across subjects, the estimated tract strengths between seed striatum and target regions will also differ?

I did not find the answer from the documents on the wiki website. Did the probtrackX take this confound into account automatically?

Did someone else encounter this problem before or know the answer？

Thanks so much！

Xuemei Lei

--
Saad Jbabdi
University of Oxford, FMRIB Centre

JR Hospital, Headington, OX3 9DU, UK

(+44)1865-222466 (fax 717)
www.fmrib.ox.ac.uk/~saad