What role did Descartes assign to the pineal gland in mind-body interaction?

In Cartesian philosophy, René Descartes identified the pineal gland as the specific site of interaction between the mind and body, two substances he considered radically dissimilar.123

Descartes reasoned that the pineal gland was the only nondouble organ in the brain, making it the necessary point where sensory information from both sides of the body could merge into a single experience. He proposed that external stimuli cause "animal spirits" to move through nerves to the pineal gland, causing it to vibrate. These vibrations were thought to give rise to emotions, passions, and perceptions, while the mind could influence the body by altering these vibrations to change bodily reactions.23

Although Descartes's specific physiological claims regarding the gland's function were incorrect, his work established the pineal gland as the "nodal point" of his dualistic theory, attempting to bridge the gap between the physical, mechanical body and the immaterial, reasoning soul.23