The variability of serial fMRI data: Correlation between a visual and a motor task

We investigated whether the intersession variability of serial fMRI studies correlates between two activation modalities, i.e. a standardized visual a nd a standardized motor task. Six volunteers were scanned in at least weekl y intervals. The number of pixels activated as well as the activation ampli tude varied widely. The maximal difference of the number of pixels activate d was 1150%, of the activation amplitude 250%. In three volunteers, the var iability was highly correlated between the two tasks. Three other volunteer s showed one outlier each. We conclude that the intersession variability is due to global factors affecting the whole brain, but that due to unpredict able outliers, using a standardized task to normalize the data of interest is of limited value. NeuroReport 11:3843-3847 (C) 2000 Lippincott Williams & Wilkins.