Symmetry, Asymmetry, Brain, and Sense Organs in Ancient Greek Medicine

Current neurophysiology accepts that sense organs are arranged in bilateral symmetry, whereas asymmetry is dominant in the brain. Symmetry and asymmetry are words of Greek origin (= symmetria and asymmetria), which are frequent in ancient medical texts, especially in those of Galen (129-216 AD), the most important anatomist and physiologist from the ancient world who lived in Rome, at the imperial court of Marcus Aurelius (161-180 AD) and his successors. In Greek, symmetria means “symmetry, due proportion, harmony among the parts, suitability”, and may be connected with the concept of health, whereas asymmetria is the opposite. As regards sense organs, Galen mentioned duality rather than symmetry, and considered it useful, because it ensures the preservation of health and body functions, when one of the pair is injured or lost. Galen established a close relationship between brain and sense organs, and believed that the brain has the same duality as the sense organs. Therefore, Galen contributed to the “obsession with brain symmetry”, which was abandoned only in the 20th century.