Passions of the Soul, by René Descartes
As the Aristotelian frameworks disintegrated in the seventeenth century, the soul ceased to be responsible for organic functions; most famously in the philosophy of René Descartes (1596–1650), it became equal to the mind [...]
[...] Descartes, in several letters as well as in his Treatise of Man (written before 1637) and The Passions of the Soul (1649), speculated that the soul exerted its functions “immediately” at or through the pineal gland. His model was hydrostatic. When the soul desires something, it makes the pineal gland move in such a way that it displaces the animal spirits to obtain the required effect. Memory, for example, was explained by the flow of animal spirits through pores in the brain substance: The flow widens the pores, and the widened pores then function as memory traces that are activated when the pineal gland pushes the animal spirits through them.
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