Neurobiological disorder: An illness of the systema nervosum caused by genetic, metabolic, or other biological factors. Many illnesses categorized as psychiatric disorders are neurobiological, including autism, bipolar disorders, obsessive-compulsive disorders, schizophrenia, and Tourette syndrome. Attention-deficit/hyperactivity disorder (ADHD) (sometimes mentioned as ADD for those without hyperactivity) is assumed to be a nervous disorder, always present from childhood, which manifests itself with symptoms like hyperactivity, forgetfulness, poor impulse control, and distractibility. These disorders include epilepsy, Alzheimer disease, and other dementias, cerebrovascular diseases including stroke, migraine, and other headache disorders, MS, paralysis agitans, neuro infections, brain tumors, traumatic disorders of the nervous system due to head trauma, and neurological disorders