brain

Old English brægen named the organ we now call the brain. The word appears in the earliest Old English texts and connects to Old High German hirni and Old Norse heili — all Germanic words for the same organ, all from the same Proto-Germanic root *bragnam. The root may relate to a word meaning 'the soft matter in the top of the head,' connected to the Latin cerebrum and Greek brégma.

For most of human history, the brain was not understood to be the seat of thought. Aristotle, in the 4th century BCE, believed the heart was the organ of cognition; the brain, he thought, was a cooling device for the blood. Egyptian embalmers, who preserved everything significant about the body, discarded the brain through the nostrils, considering it worthless. The heart was carefully removed and stored in a canopic jar.

The Greek physician Hippocrates (460-370 BCE) correctly identified the brain as the seat of intellect. Galen of Pergamon (129-216 CE) followed with detailed anatomical studies. But Aristotle's cardiac theory of cognition persisted in popular belief for centuries, which is why we still speak of heartfelt emotions, learning things by heart, and matters being heart-warming.

Modern neuroscience has made the brain the most studied object in the history of science. The Human Connectome Project, begun in 2009, attempts to map every neural connection in the human brain — approximately 100 billion neurons, each connected to thousands of others. The organ that Old English called brægen contains more connections than there are stars in the Milky Way.