In order to study how blood flows through children’s brains, researchers at Children’s Hospital in Philadelphia perform the following experiment on healthy children, ranging in age from three to 11: They insert needles into each child’s femoral artery (thigh) and jugular vein (neck), bringing the blood down from the brain. Then, they force each child to inhale a special gas through a facemask. In their subsequent Journal of Clinical Investigation article on this study, the researchers note that, in order to perform the experiment, they had to restrain some of the child test subjects by bandaging them to boards.