Subtle neurological signs (synkinesis and mirror movements) are present in normal children up until 9 or 10 years of age. In addition, speed of repetitive and sequential movements increases from 5 to 8 years of age at which time children perform these movements at close to adult speeds. Based on clinical studies of both normal children and of children with corticospinal tract lesions, it has been postulated that these subtle motor signs reflect neurodevelopmental immaturity of the intracortical and interhemispheric inhibitory systems and that their disappearance occurs as a result of maturation.