Asymmetrical Tonic Neck Reflex (ATNR)

What Is the Asymmetrical Tonic Neck Reflex (ATNR)?

The Asymmetrical Tonic Neck Reflex, commonly referred to as the ATNR, is one of the key primal/primitive reflexes present in infancy. These reflexes are automatic movements directed from the brainstem, and they help newborns survive and begin early movement and development.

The ATNR is easily identified by a characteristic posture: when a baby lies on its back and turns its head to one side, the arm and leg on that side of the body (the side the head is facing) will extend. At the same time, the arm and leg on the opposite side of the body (at the back of the turned head) will flex. This pose is sometimes called the “fencer position” or the “fencer reflex”.

The ATNR serves important foundational functions for neurological and sensory development. This reflex is directed by head movement and has connections to the vestibular system (which is important for balance and coordination), as well as muscle tone. Its activation is, in fact, partly responsible for the kicking felt by expectant parents during pregnancy, and it is reinforced during the birthing process as the baby moves and corkscrews down the birth canal. This is why practitioners often inquire about a child’s birth history when evaluating a child’s potential retained reflexes and neurodevelopment.

The ATNR prepares the brain and body for complex future skills: it lays the groundwork for eye-hand coordination, early vision development, crossing the midline, and bilateral motor control. Skills such as reading, writing, copying from a blackboard, driving, or simply turning the head to grab an object all rely on the foundational pathways established by the ATNR.

Typical Timeline of Development of the Asymmetrical Tonic Neck Reflex

The ATNR first emerges in utero. Its activation can already be observed through fetal movement patterns; the classic “kicking” felt by expectant mothers is actually a product of this reflex at work before birth.

This reflex is strongly reinforced during the birthing process itself. As the baby passes through the birth canal, the corkscrewing motion required by the ATNR further strengthens its presence.

The ATNR should be fully developed at birth. Newborns placed on their backs and having their heads gently turned from side to side will readily display the extending and flexing of their limbs, demonstrating the reflex in action.

Typical Timeline of ATNR Integration

The ATNR should integrate and be replaced by intentional, controlled movements by about six months of age. At this point, the baby develops voluntary control over head turning and coordinated limb movements, replacing the automatic fencer response.

What Symptoms Appear If the Asymmetrical Tonic Neck Reflex Is Retained?

If integration doesn’t occur, and the ATNR lingers beyond six months, it may disrupt other areas of development, setting the stage for potential motor and cognitive difficulties. A retained ATNR means this early-life reflex was not fully integrated, and it will continue to influence movement and coordination in older children and adults. A retained ATNR can manifest in a wide range of symptoms and difficulties.

Atypical or Skipped Crawling Phase

Because the ATNR strongly influences a baby’s ability to cross the midline, synchronize limb movements, and develop bilateral coordination, one of the earliest red flags is an unusual or skipped crawling phase. Unusual crawling can look like “butt scooting”, crawling with one leg out to the side, and never progressing from “army” crawling to cross-crawling/creeping on all four limbs.

Difficulty with Left–Right Discrimination and Hand Dominance

A child struggling to accurately distinguish left from right, or who does not establish a preferred (dominant) hand by ages 5–7, may have a retained ATNR.

Challenges in Eye-Hand Coordination and Visual Processing

Since the ATNR connects head movement with the arms and the visual system, retained ATNR can significantly disrupt skills like reading, writing, copying from a board, or playing ball and sports. The child may find it difficult to visually track and coordinate fine-motor activities.

Difficulties with Classroom and Everyday Tasks

Children may be unable to read or write efficiently. Tasks that seem unrelated at first—like looking over the shoulder while steering a car—can expose a retained ATNR. If a child’s arms move when their head turns, this is a sign the reflex is still active.

Potential for Misdiagnosis

When the ATNR remains active beyond infancy, it may play a role in certain challenges, such as difficulties with reading, handwriting, math concepts, attention, or visual processing. These learning challenges can sometimes look similar to, or occur alongside, conditions like dyslexia, dysgraphia, dyscalculia, ADHD, or vision differences, but the reflex itself is only one of many possible contributing factors.

What Causes a Retained Asymmetrical Tonic Neck Reflex?

A number of factors may interrupt the natural integration of the ATNR:

Insufficient Movement Opportunities in Infancy

Modern lifestyles can hinder natural development. Babies who spend considerable time in swings, bouncers, or car seats rather than having unrestricted floor and “tummy” time may not get the movement variety needed to stimulate and integrate their primitive reflexes.

Birth Experience

Atypical or traumatic birth experiences—including C-section deliveries, breech birth, or very quick labor—may interfere with the reinforcement and integration of the ATNR. Because the birthing process helps reinforce the reflex, missing this can leave it less mature.

Other Developmental Disruptions

Medical issues, premature birth, and neurological problems can also interrupt the integration pathway for the ATNR and other primitive reflexes. Please read the section entitled Regression of Milestones in our Developmental Delays Main Info Page as well as the section entitled What Can Pause, Impair, or Interrupt Brain Development? in our How a Child’s Brain Develops article for detailed information.

What Can Be Done for a Retained Asymmetrical Tonic Neck Reflex?

With the right activities and support, a retained ATNR can often be integrated later in life—sometimes even in adulthood. It’s never too late to revisit foundational movement experiences. Provide older children with opportunities for movement on the floor, including reaching, rolling, crawling, and tummy-time equivalents.

If you suspect a retained ATNR, consider seeking a qualified occupational therapist or other pediatric specialist trained in reflex integration. These therapists can perform a comprehensive evaluation and implement a tailored reflex integration plan. Please note that not all occupational therapists or doctors of physical therapy are trained to evaluate and integrate retained reflexes.

Because the ATNR can also affect visual processing, it may be beneficial to have your child evaluated by a developmental/behavioral optometrist. In addition, if you and your child experienced birth difficulties, evaluation and treatment by an osteopath and/or chiropractor could also be helpful.

About Maria Rickert Hong CHHC

Prior to working on Wall Street, she was a marketing specialist for Halliburton in New Orleans, where she also received her MBA in Finance & Strategy from Tulane University.

She is the author of the bestselling book Almost Autism: Recovering Children from Sensory Processing Disorder and the co-author of Brain Under Attack: A Resource for Parents and Caregivers of Children with PANS, PANDAS, and Autoimmune Encephalitis. She is a co-author of Reversal of Autism Symptoms among Dizygotic Twins through a Personalized Lifestyle and Environmental Modification Approach: A Case Report and Review of the Literature, J. Pers. Med. 2024, 14(6), 641.

Maria is also a Certified Holistic Health Counselor. Her work can be found on DocumentingHope.com, Healing.DocumentingHope.com, Conference.DocumentingHope.com and MariaRickertHong.com

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