Sudden rapid, recurring muscle contraction
usually a blink, sniff, twitch, or shrug
always brief, irresistible, and localized.
Frequency decreases from head to foot. Unlike a spasm, a cramp , or the movements of chorea or epilepsy , it does not interfere with other movement and can be held off for a time. It can become ingrained as a habit of which the person (most often a nervous child 5–12 years old) is unaware. Most tics are probably psychological, but similar movements occur in some physical disorders (e.g., late-stage encephalitis ). People with tics have some control over the movement but feel impelled to go through with it to feel better. Tension increases the movement's likelihood, and distraction reduces it. Psychotherapy, relaxation training, and biofeedback training have had some success in treating tics.