Kinomura, S., Larsson, J., Gulyás, G. and Roland, P.E.: Activation by attention of the human reticular formation and thalamic intralaminar nuclei, Science 271:512–515, 1996.

Blood flow in the brain was measured using positron emission tomography to test the hypothesis that the flow increased in particular areas of the brain when subjects transitioned from a relaxed state into a state of high vigilance. Blood flow in the areas of interest was measured in 10 subjects and shown to be significantly higher when the subjects underwent a transition in state. The authors concluded that increased blood flow in the brain areas studied caused (in the but-for sense) arousal and vigilance in human beings.