The Pineal Gland: A Historical Bridge Between Mind and Body

The chapter's central question

Descartes sought to find a center where sensory information from the brain would be unified and where the soul would influence body movements. He chose the pineal gland, which seemed to be unpaired on the left and right, as the location, and explained that the flow of animal energy moves the nerves and muscles. There was a clear philosophical need to explain the unity of experience even amidst faulty anatomy.

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Descartes split humans in two. The immaterial soul (Res Cogitans), which thinks and feels, and the material body (Res Extensa), which occupies space and moves like a machine. So how do the soul, which cannot be touched, and the body, which is a lump of meat, communicate?

The place Descartes pointed out was the ‘Pineal Gland’, a small organ located in the center of the brain.

According to Descartes' 17th-century physiology, when external danger is detected by the sense organs, 'Esprits animaux', a very fine substance believed to be produced in the blood, moves along the nerves and affects the pineal gland. The soul then experiences a subjective passion called ‘fear’. Although this explanation differs from modern neuroscience, it has historical significance in that it attempts to explain changes in the body and experiences of the mind as a continuous process.

Context and nuance

Descartes' 『Passions of the Soul』 asks how the mind and body interact, what physiological processes occur through passions, and how free judgment can deal with them. What makes this work unique is that mechanistic physiology and moral training coexist in one book.

From today's perspective, the pineal gland does not solve mind-body problems. This is because how matter and immaterial things act causally is still not explained. But instead of laughing at the errors of the past, it is productive to see that the problem still remains: what language should we use to describe the connection between subjective feelings and objective bodily processes?

Do not oversimplify it this way

The description of the pineal gland and the zoonotic glands is a historical hypothesis of 17th century physiology. Calling animal energy the same thing as today's neurotransmitters or action potentials erases the differences in time. Although Descartes' scientific explanation has been revised, it is still worth reading for his critical awareness of body changes, subjective experience, and preparation for action as a single process.

Philosophy in life

Have you ever been right before a presentation when your heart was pounding and your hands were shaking, and the more you urged yourself to “Please stop!” the more your body stiffened?

Noticing surroundings: If comfortable, briefly notice an object or a sound around you. There is no need to force a change in body or feeling.

Primary-source guide

Primary guide: The Passions of the Soul, especially articles 27–50, 53, and 153–161.

Pathos Editorial · Reviewed 2026-09-12