Functional magnetic resonance imaging has been used as a way to test and extend the ACT-R (adaptive control of thought-rational) theory. This chapter describes a new modeling effort that illustrates the potential of this approach, and then ends with some general remarks about the potential of such data to guide modeling efforts and the development of a cognitive architecture generally. Brain imaging has grown hand in hand with the movement to a module-based representation of knowledge in the current ACT-R theory. According to the ACT-R theory, cognition emerges through the interaction of a number of independent modules. This chapter discusses the ACT-R architecture and its application to brain imaging. It also presents a methodology for relating the profile of activity in ACT-R modules to the blood-oxygen level dependent responses from the brain regions that correspond to these modules.