Inferring individual differences in fMRI: Finding brain regions with significant within-subject correlation

Functional magnetic resonance imaging studies answer qu activation effects in populations of subjects. To begin with, this in priate modeling of the fMRI data at the within-subject level. This i extending the model to multiple subjects. There have been several att this extension, all of which have focused on inference on a single eff (e.g., fMRI response for one type of working memory). However, th erature does not seem to say much about the relevant inferential pro multiple effects are of interest (e.g., response for four different typ memory). In particular, the within subject dependence of one activat another is an important issue with a multivariate repeated measures most standard statistical methods regard such correlation as a nuisa justed for and then ignored, we develop two simple and intuitive te inference on the existence of such correlation. We demonstrate use of these tests by application to an fMRI study of attention switching. These tests are different not only from conventional tests for sphericity but also, more importantly, from the likelihood ratio test (LRT) of the relevant hypothesis. We also discuss what prompts us to look for tests different from the LRT.