Hello all,
I read that it is recommended for PPI to select a ROI from the group level of the normal first level analysis. Then take this ROI to the subject level and within this ROI look for the local maxima and extract the eighnvariame with a sphere of 6 or 8 mm.
Now my question is: If I am interested in, say, S1. What is the best approach to make sure that each subject has an extracted sphere within S1. In other words, this is what I am thinking to do and in the last step you see my probrlem :
1- create an anatomical ROI of S1 from aal.
2- mask the activation of the group with this ROI. So the remanning is activation within some voxels within S1
3- take this activated S1 and go to the subject level. Here I should insert this ROI as an inclusive mask.
4- then press and go to the local maxima.
5- create an eignvariane with a sphere of 8 mm.
Now my problem is that what if some subjects have local maxima at the edge of this activated S1. Then the created sphere may cross over and cover part of another region next to S1.
Any advice or clarification would be appreciated ,
Thanks
Aser
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