In a treatise called On the difference between spirit and soul, Qusta ibn Luqa (864–923) combined Nemesius’ ventricular localization doctrine with Galen’s account of a worm-like part of the brain that controls the flow of animal spirit between the middle and posterior ventricles. He wrote that people who want to remember look upwards because this raises the worm-like particle, opens the passage, and enables the retrieval of memories from the posterior ventricle. People who want to think, on the other hand, look down because this lowers the particle, closes the passage, and protects the spirit in the middle ventricle from being disturbed by memories stored in the posterior ventricle (Constantinus Africanus 1536, p. 310).