Activation and deactivation in blood oxygenation level dependent functional magnetic resonance imaging

Decreases in the blood oxygenation level dependent signal are somewhat puzzling for several reasons. The first is the synaptic complexity in interactive networks, and the second involves the interplay between oxidative demand and perfusion in producing signal change. The third reason involves the relativity of both activation and deactivation to the choice of the baseline condition. The fourth is that deactivations could reflect passive shunting of blood to activating areas as easily as they reflect active inhibition. However, understanding deactivations is necessary to fully understand how excitation and inhibition affect functional images. We propose strategies using convergent experiments as a means of elucidating the nature of deactivations. (C) 2003 Wiley Periodicals, Inc.