Nowadays, we see the brain as the organ responsible for our intelligence and higher mental possibilities. However, it took about 200 years before this concept was accepted. Aristotle could hardly believe how a bloodless, numb and generally not impressive-looking organ could be the source of the highest human faculties. He supposed these functions were to be contributed to the heart. Descartes saw a number of important functions in the brain, however attributed the greatest functions to the rational soul. Locke's teacher, Thomas Willis (1621-1675), paid more attention to the brain and was in 1664 the first to accurately publish a detailed work about it, named 'Anatomy of the Brain'. Willis saw that the brain tissue was not undifferentiated, as Aristotle thought, but consisted of two kinds of substances. Firstly, there is a fleshy, grey mass that forms the outer layer, also know as the cortex, (the inner part of the spinal cord and several discrete centres within the brain). Secondly, there is a fibrous white mass in the other areas. He speculated that this white mass consisted of narrow channels whose function is to distribute the "souls" that are created in the grey mass. In addition, he also accurately described the blood vessels in the brain, which proved that the brain is not a bloodless organ. Other doctors discovered that strokes can occur in the brain, and that, in case of injuries on one side of the brain, there are often paralysis or loss of feeling on the other side of the body. However, the brain only really became a topic...