Dear SPM experts,
I'm doing my first task-fMRI study using SPM 12 and am quite confused about masking. I know there are many posts about this issue in the forum, but I still can't come to an accurate conclusion after reading them, so I hope to get some help here.
By default, SPM uses an implicit mask with a threshold = 0.8 in the first-level analysis. I have two questions about this:
1. The implicit mask often dropout some important brain areas, such as OFC. Some people strongly suggest using an explicit mask with threshold = -inf, instead of the implicit mask. I’m confused about which method is more accepted in the community.
2. When setting the threshold to 0.8, the implicit mask usually includes a lot of white matter and CSF (in my case, the whole brain is included). So, in the results of first and second-level analyses, there will also be clusters composed of WM, or clusters containing both GM and WM. Should I report these results as significantly activated brain regions? Or should I apply the subject's gray matter (such as the wc1 image from segmentation) as a mask somewhere?
Any answer or discussion will be highly appreciated. Thanks in advance.
With best wishes,
Terry
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