From knowledge to belief or the misguidance of Jules Luys, an intellectual journey still relevant

ABSTRACT

A contemporary of Jean-Martin Charcot, Jules Bernard Luys was a neurologist and psychiatrist who remains known for having described the corpus Luysii, a grey subthalmic formation which became the subthalmic nucleus. His work as an anatomist is preserved in two innovative books, the first designed to give a three-dimensional view of the nervous system in 1865, and the second ushering in anatomical illustration using photography and introducing micro-photography in 1873. Splitting his time between La Salpêtrière Hospital and the Ivry asylum, Luys presented brain physiology in his book Le cerveau et ses fonctions (the brain and its functions) to shine light on its disorders, as an introduction to his voluminous Traité clinique et pratique des maladies mentales (clinical and practical treatise on mental illnesses), which already showed the work of a fertile imagination attempting to connect mental illnesses with anatomical observations expressly interpreted. His 1886 appointment at La Charité Hospital provided him with an opportunity to imitate Charcot's Lessons, so he immersed himself in the study of hysteria. With the help of a fervent believer in occultism, Gérard Encausse, who, unbeknownst to him, manipulated the young women he ran his experiments on, Luys made the most extravagant observations, believing naively in his findings and proceeding without critical analysis. This story of a great scientist, slipping into irrational thinking by abandoning the benefits of doubt, is an opportunity to explore the mechanisms leading to this deviation, which is not without parallels with more recent deviations during the AIDS and Covid-19 pandemics. © 2022 Elsevier Masson SAS