Background: Dextroamphetamine is known to have profound effects on both subjective and physiologic measurements, but it is unclear to what extent these behavioral changes are a direct result of altered regional brain activation. One method to measure this is to use functional magnetic resonance imaging (fMRI).
Methods: In the present study, fMRI was used to measure both the spatial extent of changes (the number of pixels activated) and the magnitude of the blood oxygen level-dependent (BOLD) response. We examined the effects of motor, verbal, memory, and spatial attention task during fMRI in 18 healthy volunteers. Functional MRI measurements were obtained at baseline and again 75 min after an oral dose of 25 mg dextroamphetamine.
Results: Dextroamphetamine caused a decrease in the number of activated pixels and the magnitude of the BOLD response during the three cognitive tasks tested but not during the motor task. These changes were region and task specific.
Conclusions: This is the first study to examine the effect of dextroamphetamine on the number of activated pixels and the BOLD response during the performance of a range of cognitive and motor tasks. Our results suggest that dextroamphetamine causes measurable decreases in brain activity in a variety of regions during cognitive tasks. These changes might be linked to behavioral changes observed after dextroamphetamine administration and could possibly be mediated by alterations in dopaminergic activation.