Sensory tricks in cervical dystonia: Perceptual dysbalance of parietal cortex modulates frontal motor programming

Cervical dystonia is a disabling basal ganglia disorder characterized by an involuntary head deviation to one side. A typical but also mysterious feat ure is the impressive improvement of muscle spasms and involuntary head pos ture by application of a sensory facia stimulus (sensory trick), Here, we r eport the effect of a sensory trick on cortical activation patterns in 7 pa tients with cervical dystonia by using (H2O)-O-15 positron emission tomogra phy, The application of the sensory trick stimulus, resulting in a near-neu tral head position, led to an increased activation mainly of the superior a nd inferior parietal lobule (ipsilateral to the original head turn) and bil ateral occipital cortex and to a decreased activity of the supplementary mo tor area and the primary sensorimotor cortex (contralateral to the head tur n). We propose that a perceptual dysbalance induced by a sensory trick mane uver leads to a relative displacement of the egocentric midvertical referen ce to the opposite side and a decrease in motor cortex activity. This modul ation of motor programming gives novel insights into the mechanisms involve d in sensorimotor integration in movement disorders.