The symmetric tonic neck reflex (STNR), sometimes also called the symmetrical tonic neck reflex, is another very important reflex. You’ll start to see it when your baby is 6 to 9 months old.

The STNR is a primitive reflex that is characterized by upper extremity (UE) extension and lower extremity (LE) flexion with neck extension, and by UE flexion and LE extension with neck flexion ...