A term formerly used to describe mental illnesses due to a non-psychiatric medical condition rather than a psychological cause. It is now known that all mental illnesses have at least some biological basis. Organic brain disorder is divided into three types of mental illness. The first is delirium—a state of mental confusion that develops over a few hours or days and tends to fluctuate, often rapidly. The second is dementia — a persistent state of cognitive deficit including impairment in memory. The third is amnestic disorder — an impairment to memory alone that does not involve other cognitive functions. The causes of delirium, dementia, and amnestic disorder include various general medical conditions (for example, liver disease), diseases of the brain (for example, Alzheimer’s disease, encephalitis, or a brain tumor), medications or toxins, abused substances (for example, alcohol or sedatives), poor circulation in the brain, stroke, and brain injury.
When brain tissue experiences damage or degeneration, it results in a condition known as an organic brain disorder, which manifests as impaired brain function.