The pineal gland as the hegemonikon of the microcosm: anatomical and philosophical interpretations in Descartes’ works

The pineal gland, a small, unpaired structure located at the center of the brain, was first identified as a distinct organ by Galen of Pergamon, yet its function remained obscure until the early modern period, when philosophers and physicians alike try to understand its function. This paper examines René Descartes' interpretation of the pineal gland in the treatise Le Monde and within the intellectual context of the heliocentric revolution. As research investigation methods we used social-historical documentation and hermeneutic analysis on Descartes' Le Monde and L'Homme in relation to the scientific thought of the 17th century, i.e., Harvey's anatomical achievements, and Copernicus', Kepler's, and Galileo's astronomical discoveries. In L'Homme, a chapter of his treatise Le Monde, Descartes analyzed the complex role of the pineal gland not only in a philosophical manner, but also from a medical point of view. The French thinker gave up the analogy between the gland located in the middle of the brain and the pinecone and preferred the analogy with the Sun which in ancient Greek mythology was called Helios, whose role in the cosmic system was considered to be a Hegemonikon. Thus, Descartes named the pineal gland as gland H. Inspired by Copernicus' and Kepler's heliocentric theory and by William Harvey's conception about blood circulation, Descartes has built an analogy between the Sun (Helios), heart, and gland H. As Sun (Helios) ruled the planets in its system, and heart pumped the blood into circulatory system, so gland H (pineal gland) could direct animal spirits through the nerves. Metaphors and analogy method allowed the French philosopher to establish an objective scientific presentation about pineal gland, emphasizing the macrocosm-microcosm analogy and the conceptual shift of the vital center from the heart to the brain.