A plantar reflex is a normal reflex that involves plantar flexion of the foot (toes move away from the shin, and curl down. An abnormal plantar reflex (aka Babinski Sign) occurs when upper motor neuron control over the flexion reflex circuit is interrupted. This results in a dorsiflexion of the foot (foot angles towards the shin, big toe curls up). This also occurs in babies under ~1 year, due to low myelination of the descending corticospinal tracts. As these tracts develop to adult form, the flexion-reflex circuit is inhibited by the descending corticospinal inputs, and the normal plantar reflex develops..