IN THE LATTER half of the sixth century BC, Croton was the site of the most famous medical school in Magna Graecia, where diseases of the human body were examined in a scientific and experimental manner instead of by using the contemporary supernatural, nearly magical concepts. Alcmaeon was one of the most active physicians interested in human physiology in the medical tradition of Croton. Although Alcmaeon was devoted to science and was a skillful experimentalist, little is known about his life and his exact birth date. The relative isolation of Alcmaeon from the great philosophical currents of his time probably facilitated his unprejudiced methodology and may have prevented him from disclosing his theories and demonstrating their value. He pioneered the concept of the relationship between the brain and the mind and was the first to identify the brain as the center of understanding and the essential organ for perceptions, sensations, and thoughts. Through systematic observations, Alcmaeon brought many things to light about the characteristics of the eye and the presence of channels connecting head sensory organs to the brain. He stated that the soul was immortal and introduced the tekmairesthai doctrine, through which the ideas of anamnesis and prognosis gave birth. We highlight his contributions to medical thought, and especially to neuroscience, which reveal Alcmaeon to be a thinker of considerable originality and one of the greatest philosophers, naturalists, and neuroscientists of all time.