Where did the ventricular localization of mental faculties come from?

During the Middle Ages it was widely believed that the various mental faculties-sensation, cognition, memory, and so forth-were each located in a specific part of the three ventricles that were thought to be housed in the brain. The origin of this scheme was commonly attributed to the ancient scholars, but it was rare for a specific individual to be identified as the originator. Modern researchers sometimes attribute it to Galen, but Galen was clear in his contention that the mental faculties were located in the substance of the brain rather than in the ventricles. It was only later scholars who, using Galen's anatomy as their basis, placed the mental faculties in the ventricles themselves. The system came together piece by piece over a period of centuries, probably not appearing fully in the form known to the Medieval world until the Middle Ages themselves. This article traces the development of the theory of ventricular localization of the mental faculties from the Ancient world to the early part of the Middle Ages.