Studies by Dr. Andrew Scholey, director of the Human Cognitive Neuroscience unit at the University of Northumbira: a single dose of the herbal extract gingko (which is thought to boost blood flow and increase glucose metabolism in the brain) improved the attention of students for up to six hours. (Seenan, Gerard. Oxygen and Sugar Boost Brain Power. 2001. http://www.guardian.co.uk/uk/2001/apr/highereducation.education)