slow, purposeless, and involuntary movements of the hands, feet, face, tongue, and neck (as well as other muscle groups). The fingers are separately flexed and extended in an entirely irregular way. The hands as a whole are also moved, and the arms, toes, and feet may be affected. The condition is usually caused by malfunctioning of the basal ganglia of the cerebrum. The movements may or may not continue during sleep. They cannot be arrested for more than a moment by willpower and are aggravated by voluntary movements. See also cerebral palsy.