Hi Eugene,

Thank you very much for your help.

My time series are z values (and I used age and gender as covariates, which were demeaned), is it ok?

When I calculated the ROI-to-brain voxel-wise negative FC of the thalamus as ROI by using -1 for the group mean (and 0 for the covariates) in the GLM setup, I obtained some significant correlations only with some regions in the white matter... I also tried to get the negative effect (mean) in the one sample t test by firstly multiplying the data by -1 (I attached the screenshot of the tutorial that I followed), but I obtained again significant correlations only with white matter... What do you think?

Thank you again for your help,

Matteo

2017-02-03 21:09 GMT+01:00 Eugene Duff <[log in to unmask]>:

Hi Matteo 

On 3 February 2017 at 18:17, Matteo Antonio <[log in to unmask]> wrote:

Dear FSL e-mail list,

I'm doing a whole-brain voxel-wise functional connectivity analyses with FSL for resting state fMRI data and I'm trying to perform a one-sample t test to detect the significantly positively and negatively connected regions (correlated and anti-correlated) with one ROI in my sample.

 

When I did the one sample t-test for detecting the significantly positively connected regions for the ROI, I got consistent results (I put 1 in the correspondent contrast to get the group mean in the GLM setup).

But I found strange results when I tried to get the negatively connected regions with the same ROI... According to the FSLwiki tutorial, firstly I multiplied the original data used to test the positive mean by -1, and then run the randomise function with the same GLM setup that I used for calculating the positive mean. I also tried to directly use -1 (insted of 1) in the GLM setup to get the group negative mean. But in both cases the results are very strange (and similar between each other) and seem to be incorrect.

 

I think I'm doing something wrong... Can someone help me?

Are your time series demeaned? This could cause strange results.  Really, to test negative correlations, all you should need to do is change the contrast from 1 to -1.

Eugene

 

 

Thank you so much!

Matteo