Imagination, reason, and memory are located in particular fluid-filled ventricles or 'cells' of the brain.

Long before modern functional neuroanatomy, scholars tried to put different parts of the mind in different places.

Between late antiquity and the early Middle Ages, the cell doctrine developed from Greco-Roman ideas about the brain, pneuma, and psychology. In common three-cell versions, cognitive operations were arranged along the cerebral ventricles: sensation or imagination toward the front, reasoning in a middle cell, and memory toward the rear. Different authors varied the assignments.

The diagrams were not anatomical maps in the modern sense. They combined medicine, philosophy, and theories of internal mental faculties. Manuscript illustrations circulated for centuries, and printed versions remained popular well into the Renaissance and early modern period.

Human dissection increasingly exposed the mismatch between the neat schematic cells and actual ventricular anatomy. Vesalius challenged ventricular localization, but the doctrine did not disappear immediately; later authors, including Descartes in a different form, continued to connect mental operations with ventricular structures.

Modern neuroscience localizes brain functions in neural tissue and distributed circuits. The ventricles are cavities filled with cerebrospinal fluid rather than seats of thought.

Because the doctrine existed in many variants and faded slowly, its lifespan is deliberately not quantified.