The Babinski reflex or plantar reflex is a reflex which occurs in infants when the sole of the foot is firmly stroked. By age two, the reflex should disappear. In children and adults, the appearance of this reflex is a sign of a neurological disorder which may affect the brain or spinal cord, and it usually precedes the development of more severe neurological symptoms. This makes it a useful diagnostic tool.
This reflex is named for Joseph Babinski, the French neurologist who first took note of it in his patients and described it for the medical community. It is a very useful diagnostic tool because it requires no special equipment, and it can be performed very quickly in a basic neurological exam which is designed to provide information about the general condition of a patient's nervous system.
To evoke the Babinski reflex, the sole of the foot between the heel and the toe is firmly stroked with a hard tool or a thumb. In infants, this could cause the big toe to extend, pushing outwards, and often the small toes will accompany it in a splaying motion. Infants demonstrate the reflex because their brains are not fully mature, so the protections which prevent this reflex are not yet present.
In adults, the same stroking motion should cause the toes to curl up, in a normal or negative Babinski reflex. Some people experience a neutral reflex, in which the toes remain in position. If the toes extend, it signifies a problem. The abnormal Babinski reflex in adults can occur in one or both feet, as the pathways which cause the reflex are present on the right and left side of the body. Many adults with an abnormal Babinski reflex may also experience coordination problems and other neurological difficulties.
If the Babinski reflex is detected in adults, a neurologist will usually request additional diagnostic tests. These tests are used to determine the underlying condition which allows the reflex to occur, and once a diagnosis is made, a doctor can make treatment recommendations and discuss options with the patient.
People should note that this reflex is normal in many adult animals, including most other primates and cats and dogs. Humans who happen to have a cat or dog handy can see the reflex demonstrated by gently stroking the sole of a hind foot, which should cause the animal's toes to splay outwards.