Anatomic and functional variability: The effects of filter size in group fMRI data analysis

In the analysis of group fMRI scans, an optimal spatial filter should be la rge enough to accurately blend functionally homologous anatomic regions, ye t small enough not to blur the functionally distinct regions. Hanning filte rs varying from 0.0 to 18.0 mm were evaluated in a group analysis of six he althy controls performing a simple finger-tapping paradigm. Test-retest rel iability and Talairach-based measurements of the sensorimotor region were u sed to explore the optimal filter size. Two distinct regions of functional activation were noted in the sensorimotor cortex in group images (n = 6) at both time 1 and time 2. These regions merge once the filter size exceeds a pproximately 6.0 mm. The original hypothesis that these represented a motor and sensory activation was rejected on the basis of structural and functio nal variability. A discussion of the inherent difficulties in choosing an a ppropriate filter size is presented, (C) 2001 Academic Press.