Rene Descartes, a French mathematician, philosopher, and physiologist was a pivotal figure in philosophical thinking in the 17th century, and, indeed still is today. His ideas lead him to a conceptual separation of the mind (what he referred to as “soul”) and the body. This separation between what today might be called psychological and physical phenomena, has come to be known as “Cartesian dualism”. Descartes saw the mind as having a separate status from the world of quantifiable material things such as the physical things that go on in the body. He explained the body as well as other material phenomena with reference to shapes, sizes and motions of elements of matter.
Descartes conceptual model of mind and body acknowledges that the mind and body intermingle. Sensations like burning oneself for example, are intertwined with mental reactions of pain.
Descartes hypothesized that animal spirits or pneuma served as the basis of nerve and muscle function. He theorized further that the finest particles in the blood passed through the pineal gland on their way to the brain, where they turned into animal spirits. The spirits, something like the wind, traveled to the pores in the lining of the ventricles of the brain. The nerves were seen as tubes whose function it was to carry the animal spirits from one part of the body to another. Stimulation of a sense organ activated the filaments in the nerve tubes, which conveyed the sense information to the ventricles. From there they traveled automatically, like a reflex, through the nerves to the muscles.
Also operating in Descartes’ mechanistic renderings was a rational soul that worked independently of the muscle action. The interaction between the soul and body took place, according to Descartes, in the pineal gland, and it was there that the person (but not other animals) were able to have a conscious appreciation of the sensation and it was there that voluntary movements of the muscles were initiated. The pineal gland acted as a floating valve to the third ventricle and took part in the processing of sensation, imagination, memory and the causation of voluntary bodily movements.
In this work, Descartes proposed a mechanism for automatic reaction in response to external events. According to his proposal, external motions affect the peripheral ends of the nerve fibrils, which in turn displace the central ends. As the central ends are displaced, the pattern of interfibrillar space is rearranged and the flow of animal spirits is thereby directed into the appropriate nerves. It was Descartes' articulation of this mechanism for automatic, differentiated reaction that led to his being credited with the founding of reflex theory.
Although Rene Descartes drew from the tradition of scholastics such as Thomas Aquinas, he created a shift in direction from scholastic research that was to have long-lasting impact. He agreed with Aristotle and his followers that the intellect or soul can operate independently of the body and that it is immortal. But, unlike Aristotle, Descartes saw the soul as more active, serving to create consciousness. Other functions that Aristotle saw as part of the soul, Descartes relegated to the body. These included nutritive functions (nutrition, growth, reproduction) and sense functions (perception, locomotion). Descartes conceived of these bodily functions in mechanistic terms.
Light from the object (ABC) enters the eyes and form visual images on the retina. The images are connect to the walls of the ventricle by hollow tubes representing the optic nerve. From the tubes the image is taken by animal spirits to the ventricles and from there to the pineal gland (marked H on the drawing). Here the motor response is initiated and carried through the opening 8 into the nerve to the arm muscle, which it inflates, producing movement.
A sampling of the writings of Rene Descartes
Descartes, Rene (1633). The treatise on man
Descartes, Rene (1637). Discourse on method
Descartes, Rene (1641). Meditations on first philosophy
Descartes, Rene (1649). The passions of the soul
Writings about Rene Descartes’s theories of the mind and body.
Bennett, M. R. & Hacker, P. M. S. (2002). The motor system in neuroscience: A history and analysis of conceptual developments. Progress in Neurobiology, 67, 1-52.