Right on Cue: How the Asymmetric Tonic Neck Reflex Gets Both Sides Working Together

The Asymmetric Tonic Neck Reflex helps coordinate the left and right sides of the body.

What are primitive reflexes?

A reflex is an automatic response to stimuli such as pulling your hand away when touching a hot stove. And humans are full of them. In fact, reflexes begin before your baby is even born. These are called "primitive reflexes". They are your baby's body's way of helping them function in the world after they are born until they can figure out how to operate their body on their own.

Different primitive reflexes control different parts of the body. In order for your baby to walk, get dressed, ride a bike, or open a jar, they need to coordinate their right and left sides of their body, which is what the Asymmetric Tonic Neck Reflex (ATNR) helps with. The different primitive reflexes all play a role in setting the foundation for balance, posture, and motor control. The Symmetrical Tonic Neck Reflex (STNR) is most often called the crawling reflex and helps babies separate upper and lower body movements. The Galant Reflex helps with crawling motions and body awareness. The Tonic Labyrinthine Reflex (TLR) supports balance and posture by connecting head movements and limb position. Together, these reflexes help your baby move smoothly, coordinate different parts of their body, and build the foundation for more complex movement in the future.

What is the Asymmetric Tonic Reflex?

The Asymmetric Tonic Neck Reflex helps your baby develop coordination between their head, arms, and legs. When your baby turns their head to one side, the arm and leg on that side extend while the opposite limbs bend. This reflex supports early motor development by linking the left and right sides of the body, as well as helping integrate vision and hearing.

When babies turn their heads toward a sound, or follow an object with their eyes, the reflex helps them align their gaze with their head and body movement. This connection helps the baby in noticing that sound and sight work together, which strengthens their spatial awareness and their hand-eye coordination. One example of this is when a baby hears a rattle and turns to look at it, their arm on that side might just extend to reach toward the object. That reaction is the ATNR in action!

What are issues associated with a retained Asymmetric Tonic Neck Reflex?

The ATNR should fade by around 3 months of age as babies gain more voluntary control over their movements. When the reflex lingers beyond that point, it can interfere with motor and learning development. A persistent ATNR is often linked to challenges such as poor eye tracking, difficulty balancing, messy handwriting, or not developing a clear dominant hand. It may also contribute to problems with reading, writing, listening, and comprehension, as well as trouble with activities like riding a bike, swimming, or judging distance. Children with a lingering ATNR may show robot-like walking patterns, shoulder or neck discomfort, and poor hand-eye coordination, which can make it harder to express ideas in writing and stay focused.

How to test for a retained Asymmetric Tonic Neck Reflex

You can check for the ATNR by laying your baby on their back and gently shaking a rattle to one side of their head. If the reflex is still active, their arm and leg on the side they turn toward will straighten, while the opposite arm and leg will bend. This movement should fade around the 3 month mark.

What can you do about a retained Asymmetric Tonic Neck Reflex?

If you test the ATNR and you notice that your baby still strikes the fencer's pose, it may suggest the reflex is lingering for longer than it should. According to the National Library of Medicine, "... the tonic neck reflex is an essential primitive reflex that contributes to early motor development and normally disappears by 3 months of age," (1). At this point, monitoring whether the ATNR continues past that time is important, since its persistence can lead to developmental delays and more. You may consider either making an appointment with your doctor or meeting with a specialist. Early intervention is key.

Sources:

1. Arcilla, C. K., & Vilella, R. C. (2023, May 1). Tonic Neck Reflex. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK559210/

2. "Retained Primitive Reflexes as a Sign of Brain Imbalance", Brain Balance Centers, https://www.brainbalancecenters.com/blog/retained-primitive-reflexes-sign-brain-imbalance

3. Understanding Primitive Reflexes: A Dynamic perspective on Sensory Motor Development. (n.d.). https://sensoryhealth.org/node/2060

4. KidsCare Home Health & By KidsCare Home Health. (2025, July 21). What is asymmetric tonic neck reflex (ATNR) in newborns? KidsCare Home Health. https://kidscarehomehealth.com/what-is-asymmetric-tonic-neck-reflex/

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