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Descartes's Ambiguous Legacy

This "pre-cerebral" view of the mind disappeared in the 1600s, in the wake of advances in physics, anatomy, and chemistry. Galileo Galilei (1564–1642) and other natural philosophers challenged the physics of Aristotle (384–322 B.C.E.), replacing it with a new "mechanical philosophy" in which mechanical forces acting on atoms or other small particles produced all physical change. In the 1630s the French philosopher René Descartes (1596–1650) used the new mechanical philosophy to offer a novel description of the body. He no longer relied on vegetative or vital souls to produce the body's functions. Instead, he proposed that the body was made of particles that obeyed the laws of physics. A body was no different from a mechanical doll: neither needed a soul to drive its movements. Instead, Descartes envisioned nerves as a system of cords and inflating tubes that mechanically produced involuntary movements.

Descartes managed to take a crucial step towards a science of the nervous system, despite the fact that he was woefully confused about the brain. He accepted the medieval notion of spirits flowing through the ventricles. He even used it to determine where the rational soul was located. For Descartes, it was obvious that the pineal gland, which was believed to dangle over the ventricles, had to be where the rational soul influenced the spirits, steering them toward different nerves in order to produce voluntary movements.

This scenario, as strange as it may seem to the modern reader, accorded with Descartes's overall philosophy. He believed that nature, including the human body, was composed solely of passive matter. The human mind, on the other hand, was completely immaterial and not subject to the laws of nature. Thus Descartes required a site where the immaterial and material could intersect. The pineal gland fit all of these requirements. It would take a separate revolution in anatomy before the brain could be appreciated as more than a bowl of curds.

Additional topics

Science EncyclopediaScience & Philosophy: Methane to Molecular clockMind - The Mind Before Neurology, Descartes's Ambiguous Legacy, Thomas Willis And The Birth Of Neurology