It is the original Babinski’s: dorsiflexion (or extension) of the big toe in response to stroking of the lateral
aspect of the sole. In other words, the big toe goes up. Except for infants (where it is normal), this indicates a lesion of upper motor neurons or their pyramidal tracts. It also can occur in metabolic involvement of these tracts, such as meningitis, seizure, overdose, and hepatic/renal encephalopathy. Dorsiflexion of the big toe also may be associated with fanning out of the other toes (as in Babinski’s description), yet this is not a requirement for the response to be abnormal. An extensor plantar response (or Babinski) is an excellent bedside test: sensitive, specific, and able to pinpoint the lesion.