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![Descartes' (1596-1650) idea of vision, [1692]. The passage of nervous impulses from the eye to the pineal gland and so to the muscles. From Rene Descartes' Opera Philosophica (Tractatus de homine), 1692. (Oxford Science Archive/Print Collector/Getty Images)](https://www.salon.com/app/uploads/2021/05/descartes-pineal-gland-0514211.jpg "The mysteries of the pineal gland")