Historically, the search for the cause of a disorder of the nervous system has been focused on finding morphological or chemical abnormalities, while symptoms and signs of many disorders of the nervous system can be caused by changes in function other than those that are not directly caused by morphological or chemical abnormalities.

It is well known that activation of neural plasticity is an effective means for treating disorders of the nervous system, but it is less recognized that expression of neural plasticity can also cause symptoms and signs of disorders of the nervous system, and such facts have received less attention than morphological abnormalities.

The focus on morphological changes rather than functional changes for diagnosis and treatment, and for describing the pathology of disorders of the nervous system, is natural: morphological abnormalities (pathologies) are easy to visualize but it is difficult to determine the cause of functional changes. The focus on easily observable factors such as morphological changes is most aptly illustrated through the story about the drunken man who looks for his lost keys under the streetlight – not because this was the place he lost his keys, but because there was better light there.

In a similar way, the focus on genetically related disorders has been on a person's genetic makeup, but genetics alone do not determine whether a person develops the disease in question.