Asymmetrical tonic neck reflex

Asymmetrical Tonic Neck Reflex (ATNR)

An infant displaying the Asymmetrical Tonic Neck Reflex

The asymmetrical tonic neck reflex (ATNR) is a type of primitive reflex observed in newborn humans. It typically diminishes around the age of six months, being replaced by more complex and voluntary motor behaviors.

Description

When an infant's head is turned to one side, the arm and leg on that side will extend, while the arm and leg on the opposite side flex. This reflex has been colloquially termed the "fencing reflex" due to its resemblance to the en garde position in classical fencing.

Significance

ATNR is a normal reflex in infancy but its presence beyond the typical age can suggest potential developmental concerns.

Implications of Prolonged ATNR

When ATNR and other primitive reflexes like the tonic labyrinthine reflex (TLR) persist beyond the early months of life, they may indicate developmental delays, rendering the reflex as atypical or abnormal.

• Cerebral Palsy: Children with this condition might exhibit more pronounced and persistent ATNR.
• Functional Hindrances: Persistent ATNR and TLR can impede activities such as rolling, hand-to-hand coordination, or bringing hands to the mouth.
• Physical Deformities: Over time, ATNR might contribute to spinal curvature (scoliosis), while both ATNR and TLR can cause the thighbone's head to misalign, leading to partial (subluxation) or complete (dislocation) misplacement from the hip socket.

Early intervention with comprehensive occupational therapy is highly recommended when abnormal reflexes like ATNR persist.

Fencing Response in Adults

The fencing response is not limited to infants. In adults, it can be observed following mechanical forces applied to the head, especially in contact sports scenarios. Indicative of traumatic brain injury, this transient response points towards moderate forces impacting the brainstem.

See Also

• Primitive reflexes
• Tonic labyrinthine reflex
• Developmental milestones

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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.