How did Descartes believe mental attitudes could influence bodily passions?

In Cartesian philosophy, René Descartes proposed that the mind and body are distinct substances that interact within the pineal gland, the only non-double organ in the brain.12

Descartes argued that external stimuli cause vibrations in the pineal gland, which give rise to emotions and bodily actions through a reflex arc. While the mind cannot directly command bodily reactions—such as willing the body to fight—it can influence these physical outcomes by altering mental attitudes. By changing one's mental state, the mind can shift the vibrations of the pineal gland from those associated with one passion (such as fear) to those associated with another (such as courage).2

This capacity for the mind to regulate bodily passions through the adjustment of mental attitudes serves as a foundation for Descartes's defense of free will and the mind's ability to exert control over the body.2