From 1612, when he left La Flèche, until 1628, when he settled in Holland, Descartes spent much of his time in travel, contemplation, and correspondence. From 1628 until his ill-fated trip to Sweden in 1649 he remained for the most part in Holland, and it was during this period that he composed a series of works that set the agenda for all later students of mind and body. The first of these works, De homine  was completed in Holland about 1633, on the eve of the condemnation of Galileo. When Descartes' friend and frequent correspondent, Marin Mersenne, wrote to him of Galileo's fate at the hands of the Inquisition, Descartes immediately suppressed his own treatise. As a result, the world's first extended essay on physiological psychology was published only well after its author's death.
In this work, Descartes proposed a mechanism [see figure 2] 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 generally being credited with the founding of reflex theory.
Although extended discussion of the metaphysical split between mind and body did not appear until Descartes' Meditationes, his De homine outlined these views and provided the first articulation of the mind/body interactionism that was to elicit such pronounced reaction from later thinkers. In Descartes' conception, the rational soul, an entity distinct from the body and making contact with the body at the pineal gland, might or might not become aware of the differential outflow of animal spirits brought about through the rearrangement of the interfibrillar spaces. When such awareness did occur, however, the result was conscious sensation -- body affecting mind. In turn, in voluntary action, the soul might itself initiate a differential outflow of animal spirits. Mind, in other words, could also affect body.
The year 1641 saw the appearance of Descartes' Meditationes de prima
philosophia, in quibus Dei existentia, & animae à corpore distinctio,
In 1649, on the eve of his departure for Stockholm to take up residence as instructor to Queen Christina of Sweden, Descartes sent the manuscript of the last of his great works, Les passions de l'ame, to press. Les passions [see figure 3] is Descartes' most important contribution to psychology proper. In addition to an analysis of primary emotions, it contains Descartes' most extensive account of causal mind/body interactionism and of the localization of the soul's contact with the body in the pineal gland. As is well known, Descartes chose the pineal gland because it appeared to him to be the only organ in the brain that was not bilaterally duplicated and because he believed, erroneously, that it was uniquely human.
In February of 1650, returning in the bitter cold from a session with Queen
Christina, who insisted on receiving her instruction at 5 a.m., Descartes
contracted pneumonia. Within a week, the man who had given direction to
much of later philosophy was dead. By focusing on the problem of true and
certain knowledge, Descartes had made epistemology, the question of the
relationship between mind and world, the starting point of philosophy. By
localizing the soul's contact with body in the pineal gland, Descartes had
raised the question of the relationship of mind to the brain and nervous
system. Yet at the same time, by drawing a radical ontological distinction
between body as extended and mind as pure thought, Descartes, in search of
certitude, had paradoxically created intellectual chaos.
Wozniak, Robert H. "Mind and Body: Rene Déscartes to William James"
Bryn Mawr College, Serendip 1995
Originally published in 1992 at Bethesda, MD & Washington, DC by the National Library of Medicine and the American Psychological Association.
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