Abstract Details Title On the Seat of the Soul: Descartes’ Pineal Gland Topic Research Methodology, Â鶹´«Ã½Ó³», and History Presentation(s) P7 - Poster Session 7 (5:30 PM-6:30 PM) Poster/Presentation Number 6-005 Objective To describe the understanding of the pineal gland and its function by Descartes and his 17th century contemporaries. Background The function of the pineal gland remained a mystery until 1958 when American dermatologist, Aaron Lerner, discovered a molecule produced exclusively by the pinealocyte, which he called melatonin. Design/Methods Literature review Results Descartes contended that rational thought was the necessary and sufficient condition of the soul, and that the pineal gland was the seat of rational thought. The pineal gland held this seat because it was thought to be the only midline structure that was single and mobile. Its singleness allowed for a unity of inputs from the nervous system, and its mobility allowed for redirection of airy spirits within the ventricles to animate the body. Curiously, cerebrospinal fluid was discovered in the ventricles before Descartes’ lifetime, but this fact must not have been well known. Conclusions Though there is no clear connection between melatonin, rational thought, voluntary movement, and sensation, Descartes and his contemporaries accurately understood that the pineal gland had far-reaching influence beyond its location. Authors/Disclosures Rahul D. Abhyankar, MD (JWM Neurology) PRESENTER No disclosure on file