tonic neck reflex, a normal response in newborns characterized by extension of the arm and the leg on the side of the body to which the head is quickly turned while the infant is supine and to flex the limbs of the opposite side. The reflex, which prevents the infant from rolling over until adequate neurological and motor development occurs, disappears by 3 to 4 months of age, to be replaced by symmetric positioning of both sides of the body. Absence or persistence of the reflex may indicate central nervous system damage. Also called asymmetric tonic neck reflex. See also symmetric tonic neck reflex.
