Tic: A repetitive movement that is difficult, if not impossible to voluntarily control. Tics can affect any group of muscles. The most common are facial tics, such as eye- blinking, nose-twitching, or grimacing. Tics that affect the muscles used to produce speech are known as vocal tics, and can range from grunts or whistles to the repetition of complete words or phrases. Complex motor tics involve multiple, sequenced movements, and can include behaviors such as twirling in place, tapping a certain number of times, or stooping to touch the ground. Tics are believed to arise from differences in or damage to the basal ganglia, a structure deep within the brain that controls automatic movements and that also affects impulsivity.