Task-specific deactivation patterns in functional magnetic resonance imaging

In general, image analysis of cognitive experiments using functional magnet ic resonance imaging techniques has emphasized those regions of the brain w here increases in signal intensity, with regard to the reference state, are associated with activation. Nevertheless, a number of recent papers have s hown that there are areas of deactivation as well. In this study, we have u sed a univariate analysis and echo-planar functional magnetic resonance ima ging to address the relationship of the reference state to the deactivation s. We employed two dichotomous covert tasks, orthographic lexical retrieval and pure visual retrieval, to contrast with the reference state (baseline) of silent counting. Our analysis yielded extensive, task-specific landscap es of regional incremental and decremental responses, We have specifically demonstrated that the decremental responses are not due to activation in th e reference state. We have also demonstrated that they are not an artifact of a specific part of the image analysis, and propose that they represent a physiological, task specific signal that should be considered an integral component of neural networks representing brain function. (C) 1999 Elsevier Science Inc.