TESTS FOR DISTRIBUTED, NONFOCAL BRAIN ACTIVATIONS

Most approaches to detecting changes in functional brain images assume that activations are focal or very localized. However, the brain's re sponse to cognitive of sensorimotor challenge may be spatially or anat omically distributed. In this paper we consider the usefulness of a te st based on the mean sum of squares of statistical parametric maps. Th e performance of this test is evaluated using simulated and real data and is compared to the gamma(2) test, a test of the size of the activa ted region, and a focal activation test based on the intensity of loca l maxima. We demonstrate that the mean sum of squares test is more sen sitive to nonfocal signals and propose that it could be used to comple ment approaches that are more sensitive to focal activations. (C) 1995 Academic Press, Inc.