The Babinski reflex, also known as the plantar reflex, is a fundamental test used during a neurological examination to assess the health of the central nervous system. This involuntary response is triggered by a physical stimulus applied to the sole of the foot. Observing the toe movement provides insight into the functional integrity of the neural pathways connecting the brain to the spinal cord. French neurologist Joseph Babinski first documented this reflex in 1896, and it remains a standard assessment tool because the expected toe response changes significantly with maturity.
How the Reflex is Elicited
Performing the Babinski reflex test involves a specific, controlled stimulation of the foot’s sole. A medical professional typically uses a blunt instrument, such as the handle of a reflex hammer, to apply firm pressure. The stimulus begins at the heel and travels upward along the lateral edge of the sole. The line of stimulation then curves inward, moving across the ball of the foot toward the base of the big toe. This precise path of sensory input travels through nerves, sending a signal up to the spinal cord and brain, resulting in the motor output of the toes.
Interpreting the Response Based on Age
The way the toes react to the stimulation is interpreted differently depending on the age of the individual being tested. In healthy adults and children older than approximately two years, the expected, or “normal,” response is for the toes to curl downward. This movement is called plantar flexion, and a response of this nature is sometimes referred to as a negative Babinski sign. Alternatively, the toes may show no movement at all, which is also considered a typical adult response.
Conversely, a different movement pattern is considered normal in infants and very young children. When the sole of an infant’s foot is stroked, the big toe moves upward, while the other toes fan out and separate. This response is known as a positive Babinski sign, and it is an expected finding in children up to about 18 to 24 months of age.
The shift from the infant response to the adult response occurs because the nerve fibers in the corticospinal tract—the main pathway for motor control—become fully insulated through a process called myelination. Once this insulation is complete, the adult-type response takes over. The persistence of the positive reflex beyond toddlerhood suggests that this maturation process is incomplete or that there is a problem with the neural signaling.
Neurological Significance of an Abnormal Result
When the positive, upward-fanning reflex is observed in an individual over the age of two, it indicates a problem within the central nervous system. This finding suggests damage to the corticospinal tract, the long nerve pathway that relays movement commands from the brain down to the spinal cord. This pathway is a component of the upper motor neuron system, and its dysfunction prevents the proper regulation of the reflex arc. The presence of this abnormal reflex prompts a detailed medical investigation to identify the cause of the damage. Conditions that interrupt the flow of signals along this tract include acute injuries, such as a stroke or traumatic spinal cord injury, or progressive neurological diseases like multiple sclerosis, ALS, or a brain tumor.