"Although widely used to assess pain in neonates, withdrawal reflexes and facial movements do not necessarily represent conscious perception of pain. Full-term neonates exhibit a “cutaneous withdrawal reflex” that is activated at a threshold much lower than that which would produce discomfort in a child or adult. This threshold increases with PCA, suggesting that the capacity of the neonate to distinguish between noxious and nonnoxious stimuli is maturing. Furthermore, flexion withdrawal from tactile stimuli is a noncortical spinal reflex exhibited by infants with anencephaly and by individuals in a persistent vegetative state who lack cortical function. Behavioral studies have also identified a distinct set of neonatal facial movements present during invasive procedures such as heel lancing but absent during noninvasive procedures. These facial movements, which are similar to those of adults experiencing pain, were evident in neonates at 28 to 30 weeks’ PCA but not at 25 to 27 weeks’ PCA. Facial movements may not necessarily be cortically controlled. One study found no difference in facial activity during heel lancing of neonates with and without significant cortical injury, suggesting that facial activity even around 32 weeks’ PCA may not represent conscious perception of pain."