Brain diseases are the most cruel natural processes, but they provide an objective view of human nature that reveals the fascinating complexity of our minds. Abnormal electrical activity of the brain can produce sensory or motor epilepsy, or affect areas that produce deep psychological and ecstatic experiences. Neuroscience provides evidence that the mind does not consist in "psychological" processes, but in physical events that take place in the brain. The disintegration of the self produced by several diseases indicates that the Cartesian idea of the self, a physical body with a soul, which was conceived as a homogeneous supernatural substance, is unjustified. The success of psychoactive drugs in treating emotional and behavioral abnormalities also shows that emotions and behavior are physical processes.