Identity theory developed in the 1950s and is associated with such philosophers as J.J.C. Smart, U.T. Place and Herbert Feigl. The theory goes all the way back to the 17th century, but was especially influenced by modern research into brain function that suggested that different parts of the brain seemed to be associated with different actions. This had long been suggested by earlier research conducted in the 19th century by such figures as Dr. Paul Broca (1824-1880) and Dr. Carl Wernicke (1848-1904).

The theory simply states that when we experience something - e.g. pain - this is exactly reflected by a corresponding neurological state in the brain (such as the interaction of certain neurons, axons, etc.). From this point of view, your mind is your brain - they are identical.