Meyssonnier was physician to King Louis XIII and professor of surgery in Lyon. The main body of his work can be found in the Pentagonum philosophico médico and, in particular, in the republication of the Miroir de beauté et de santé corporelle by Louis Guyon de la Nauche (1625), after 1633. Following successive rewording and expansion, this work became the leading practical and theoretical medical course in French. It was published the same year as the posthumous edition of Descartes’ Treatise on Man (1664) and contains numerous references to Dioptrics, Passions of the Soul, and the letters exchanged with Descartes at the beginning of the 1640s.

Meyssonnier was introduced to Descartes by Mersenne, to whom he had sent Pentagonum on February 25, 1639. In a letter to Mersenne dated January 29, 1640, Descartes reports that he had received him in person. He also expresses reservations regarding the mix of “astrology, palmistry, and other such nonsense” that he believes punctuates the volume (AT III 15). In a brief letter to Meyssonnier of this same date and another more detailed one that was addressed to him care of Mersenne, Descartes responds to this royal physician's apparent inquiries concerning the function of the pineal gland (or conarium) and whether corporeal memories are stored there exclusively (see memory). First, he explains that the function of the pineal gland, given its unity, mobility, and unique position near the center of the brain, is to unite (but not preserve) the innumerable impressions that are received by the two eyes, two ears, and other senses before they are perceived by the soul.