It is assumed that all psychological and behavioral processes, whether normal or abnormal, are a result of normal or deranged brain function. Only disorders with a known organic cause are called organic mental disorders. Thus, organic mental disorders are behavioral or psychological disorders associated with transient or permanent brain dysfunction and include only those mental and behavioral disorders that are due to demonstrable cerebral disease or disorder, either primary (primary brain pathology) or secondary (brain dysfunction due to systemic diseases). The use of term organic here does not imply that other psychiatric disorders are ‘non-organic’ in the sense of having no biological basis. It simply means that the organic mental disorders have a demonstrable and independently diagnosable cerebral disease or disorder, unlike other psychiatric disorders that do not at present. In the present context, the term "organic" means simply that the syndrome so classified can be attributed to an independently diagnosable cerebral or systemic disease or disorder. The term "symptomatic" is used for those organic mental disorders in which cerebral involvement is secondary to a systemic extra cerebral disease or disorder (ICD-10).