Dextroamphetamine did not simply increase brain blood flow everywhere in a small PET experiment. Its regional effects depended on which cognitive task participants performed, underscoring the limits of interpreting more activation as universally better function.
The study examined eight healthy volunteers using oxygen-15 water PET to measure regional cerebral blood flow. Dextroamphetamine, 0.25 mg/kg, and placebo were given in a double-blind, counterbalanced design two hours before imaging.
Participants completed the Wisconsin Card Sorting Task and Raven’s Progressive Matrices, each with a corresponding sensorimotor control task. The analysis examined task-related regional activation rather than drug effects in isolation.
The researchers did not find significant drug or task effects on global blood flow or carbon-dioxide pressure. Regional findings nevertheless differed. In a left inferior-frontal region, dextroamphetamine increased flow during card sorting but decreased it during Raven’s matrices.
In the right hippocampus, the direction reversed: flow decreased during card sorting and increased during Raven’s matrices. The pattern was described as task-specific focusing of neural activity.
Regional cerebral blood flow is a physiological correlate of activity under the tested conditions. It is not a direct count of neurons, a measurement of drug concentration, or an independent verdict about cognitive competence.
The authors proposed a neurobiological explanation involving task-specific signal augmentation. That interpretation should remain distinct from the actual observations and from broader claims about every aspect of cognition.
Eight healthy volunteers provide limited information about variation across people. The experiment also tested one dose and selected tasks, not dependence, uncontrolled intoxication or complex driving.
The findings support considering the interaction among drug, task and brain region. An isolated increase or decrease cannot be labeled beneficial or harmful without understanding the function being measured and the accompanying behavior. Individual forensic conclusions require different, case-specific evidence.
Related reading: Selected performance improvements in human methamphetamine experiments.