Functional MRI (fMRI) provides a noninvasive method for mapping brain functional activity based on blood oxygenation level dependent (BOLD) image contrast that is primarily due to localized increases in perfusion. Recently, Malonek and Grinvald (Science 272:551-554, 1996) suggested that during sustained functional activation, the increases in perfusion were spread over a much larger area than the localized electrical activity. In this study, it is demonstrated that the spatial distribution of the BOLD fMRI signal during sustained stimulation of rat whiskers has the same spatial pattern and dimension as that of neuronal electrical activity in the rat whisker barrels.