A primitive reflex elicited by mildly noxious mechanical stimulation of the sole of the foot.  The normal adult responds with curling of the toes (plantar flexion).  An individual whose corticospinal tract is not functioning correctly responds with extension of the great toe and fanning of the other toes (dorsiflexion).  This abnormal response is also called the Babinski sign.  It is seen in the normal infant under a year of age whose corticospinal tracts are not yet myelinated and in an adult whose corticospinal tracts have been injured in some way.