ABSTRACT
One of the best means of developing a neuropsychological hypothesis about a specific behavior is to study groups of people who can or cannot produce this behavior and learn what common factor or factors distinguish these groups. In contrast to the psychodynamic theories of Freud, one thread that might unite those states that lead to creativity—including resting, relaxing, dreaming, and depression—are alterations of the brain's neurotransmitter systems, primarily a reduction of catecholamines, including norepinephrine. Brain levels of norepinephrine might influence creativity because they moderate the size of neuronal networks. Many creative people have related that after discovering an unresolved problem, they are unable to immediately to solve this problem. Sometimes, after a few days, weeks, or months, suddenly the solution of this problem might come to them. The ability to suddenly understand the solution of a problem suggests that the brain has been actively manipulating stored knowledge. Wallas called this process of subconscious knowledge manipulation "incubation.".
