Plato is one of the earliest philosophers to reference the brain. In Timaeus, he suggests that the brain is the “seat of reasoning” and the highest function of the human soul. He through the brain was where logical thought resided, which is pretty spot-on considering modern neuroscience. However, he also believed that the soul has three parts: reason (in the brain), spirit (in the chest), and appetite (in the stomach). This division of the soul is a bit more metaphorical and symbolic than scientifically proven.
While his understanding of the brain’s importance for reasoning was ahead of his time, Plato missed the mark by attributing things like emotions and desires to other parts of the body, instead of seeing them all connected within the brain and central nervous system. His philosophical musings set the groundwork, though, for future thinkers to explore the mind-body connection.