A distinction is often made in the viewpoint of mind between the mind and the brain, and there is some disagreement as to their exact relationship, primary to the mind-body problem. The brain is defined as the physical and biological matter enclosed within the skull, responsible for all electrochemical neuronal processes. The mind, however, is seen in terms of mental attributes, such as beliefs or requests. Some believe that the mind exists in some way autonomously of the brain, such as in a soul or epiphenomenon. Others, such as strong AI theorists, say that the mind is straightly analogous to computer software and the brain to hardware.