The asymmetrical tonic neck reflex (ATNR) is a primitive reflex found in newborn humans, but normally vanishes around six months of age.
It is also known as the "fencing reflex" because of the characteristic position of the infant's arms and head, which resembles that of a classically trained fencer. When the face is turned to one side, the arm and leg on the side to which the face is turned extend and the arm and leg on the opposite side bend.
The presence of the ATNR, as well as other primitive reflexes, such as the tonic labyrinthine reflex (TLR), beyond the first months of life may indicate that the child has developmental delays, at which point the reflex is atypical or abnormal. For example, in children with cerebral palsy, the reflexes may persist and even be more pronounced. As abnormal reflexes, both the ATNR and the TLR can cause problems for the growing child. The ATNR and TLR both hinder functional activities such as rolling, bringing the hands together, or even bringing the hands to the mouth. Over time, both the ATNR and TLR can cause serious damage to the growing child's joints and bones. The ATNR can cause the spine to curve (scoliosis). Both the ATNR and TLR can cause the head of the thighbone to partially slip out (subluxation) or completely move out of the hip socket (dislocation). When abnormal reflexes persist in a child, early intervention involving extensive physical therapy can be beneficial.
The "Fencing Response" occurs in adults as a result of mechanical forces applied to the head, typically associated with contact sports. The Fencing Response is transient and indicates moderate forces applied to the brainstem, resulting in a traumatic brain injury.
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Also children turn their head to one side, then extend their arms and legs on that side. The arms and legs on the other side bend in line with the head.