Increased sensitivity in FMRI group analysis using mixed-effect modeling

In functional Magnetic Resonance Imaging group studies, uncertainties on the individual BOLD responses are not taken into account by standard detection procedures, which may limit their sensitivity. Mixed-effect models have been introduced to derive decision statistics that weight the subjects according to their reliability. To date, however, the associated statistical tests are almost not used by investigators, partly because they are inexact in that they control only approximately the false positive risk. We tackle this problem using a permutation testing framework that yields exact tests under mild nonparametric assumptions. This approach enables us to evaluate the sensitivity of mixed-effect statistics on a mental calculation experiment involving men and women.