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What Is Asymmetric Tonic Neck Reflex (ATNR) in Newborns?

reason for asymmetrical tonic neck reflex

Humans are born with primitive or innate reflexes. These automatic motor patterns and reactions emerge during fetal life and continue until replaced with higher-level reactions during infancy. One of these innate reflexes is the Asymmetric or Asymmetrical Tonic Neck Reflex (ATNR).

Today’s post will examine this phenomenon and define asymmetric tonic neck reflex, including its timeline and integration in infants. We will also explain the significance of retained ATNR and why monitoring the integration of asymmetrical neck tonic reflexes during infant development is essential.

What Is Asymmetrical Tonic Neck Reflex?

Let’s begin by answering this question: What is asymmetrical tonic neck reflex in newborns, and why is it essential for development?

WebMD’s asymmetric tonic neck reflex definition is as follows:

“Asymmetric tonic neck reflex, or ATNR, is one of the primitive reflexes that babies experience as part of brain development. These reflexes are crucial because they help your baby to survive and thrive.”

This primitive reflex develops in the womb and can be responsible for a baby’s “kicking” in utero. It can also occur during birth as the fetus innately ‘unwinds’ while passing through the birth canal during vaginal delivery. So, how does ATNR work?

The ATNR is visible when a baby’s head turns. When turned to one side, the asymmetric tonic neck reflex is responsible for the arm on the same side to reflexively extend straight out. At the same time, the arm on the other side will bend at the elbow. The asymmetrical tonic neck reflex is often called the ‘fencer’s reflex’ because the baby’s body position resembles a fencer’s pose. So, if the baby’s head is turned left (with the jaw over the shoulder), the left arm will extend straight out while the right arm bends at the elbow.

What is the significance of asymmetric neck tonic reflex in newborns? Babies’ asymmetric neck tonic reflex supports self-preservation and helps with movement and development. These primitive reflexes are indicators of nervous system function and development and help infants explore and interact with their environment before purposeful thought develops. For this reason, pediatricians assess this innate reflex by performing an asymmetric tonic neck reflex test during newborn exams.

ATNR Timeline

Asymmetric tonic neck reflexes develop in fetuses after eight to twelve weeks of gestation as their bodies move and trigger this reflex. The ATNR continues after birth and is one of the more recognizable reflexes in infants.

The asymmetrical tonic neck reflex begins to fade around 3-4 months as the motor system advances. Around this time, infants begin to display purposeful movements, like reaching and grasping.

The asymmetric neck tonic reflex typically disappears or “integrates” within six to eight months. Integration means that the reflex does not dictate the movement of the limbs. Instead, babies begin making intentional movements to achieve a goal, demonstrating motor control and coordination. For this reason, an asymmetric tonic neck reflex in adults or children past the integration age is atypical.

Therefore, let’s explore what it means if this sequence of development does not occur, i.e., what if the asymmetric tonic neck reflex does not disappear according to the typical timeline?

What is a Retained Asymmetrical Neck Tonic Reflex?

When does the asymmetrical tonic neck reflex integrate or stop occurring? Typically, it disappears within a baby’s first year (around month 6). If this does not happen, a retained asymmetric neck tonic reflex occurs. Unfortunately, the persistent presence of the ATNR may indicate an underlying issue and impact motor development. Therefore, it’s important to explore why a persistent ANTR is occurring.

Causes of Retained ANTR

What causes retained asymmetric tonic neck reflex in newborns? There are many causes for an ATNR not integrating within the expected timeline, including:

  • Atypical or delayed development in babies may impact the integration of innate reflexes like ANTR.
  • Premature births often result in immature nervous systems, which can retain ANTR beyond the expected timeline.
  • Some neurological conditions, like cerebral palsy, brain injury, or spinal cord disorders, may affect ATNR development and integration because they disrupt regular nervous system functioning.
  • Certain genetic conditions or syndromes can affect the nervous system development and motor control, contributing to atypical innate reflex progression.
  • Limited opportunities for movement due to sedentary lifestyles or medical conditions may delay reflex integration.

Symptoms of Retained Asymmetric Neck Tonic Reflex

The symptoms of retained asymmetrical neck tonic reflex can vary from baby to baby. However, here are some to look for if you are concerned.

  • Delays in meeting motor development milestones, such as crawling or walking
  • Difficulty coordinating fine motor movements (for example, writing, drawing, buttoning)
  • Difficulty with posture control and balance
  • When coordinating movements with both sides of the body is challenging for babies
  • Difficulty with hand-eye coordination while manipulating objects (like utensils)
  • Challenges with sensory processing

What is Unintegrated Asymmetric Neck Tonic Reflex?

asymmetric tonic neck reflex persistence

Unintegrated asymmetrical tonic neck reflexes and retained ATNR are similar but different concepts. When the asymmetric tonic neck reflex is “unintegrated,” it means that it is present yet not coordinated or functional.

This lack of coordination or function often disrupts motor coordination, causing delays in achieving motor milestones and challenges with hand-eye coordination and bilateral movements.

For example, infants with an unintegrated asymmetric tonic neck reflex may compensate for these difficulties by relying more on one side of the body or using irregular movements to achieve a task.

When to Seek Treatment Involving ATNR

It’s important to remember that every baby develops differently, and not hitting milestones in sync with others is not an immediate cause for alarm. However, if an infant’s asymmetrical tonic neck reflex continues beyond expectations or interferes with their motor development and overall function, it’s best to consult a medical professional.

For example, suppose your baby struggles to maintain balance or has difficulty with visual tracking. In that case, it may be an atypical presentation of ATNR and worth exploring with your pediatrician or a speech or occupational therapist.

What Can I Do if My Child Has an Unintegrated ATNR?

If your infant displays unintegrated asymmetric tonic neck reflex symptoms, there are several ways to promote integration to support their motor development. First and foremost, consult with a pediatrician, physical therapist, or occupational therapist to assess your child’s motor skills, identify areas of concern, and recommend interventions to help.

At home, you can engage the infant in gentle movements and activities to promote reflex integration (i.e., crawling, rolling, or other activities that involve crossing the body’s midline). Also, bilateral coordination can be encouraged with movements and activities involving both hands, like crawling or catching a soft ball or toy.

Parents can also consider pediatric occupational or physical therapy with a therapist experienced in treating motor development and innate reflexes. These pediatric therapists provide personalized interventions, asymmetric tonic neck reflex exercises, and activities that can help integrate the ATNR and improve the child’s overall motor function.

Parenting newborns is exciting and wonderful. Watching these tiny people grow, learn, and experience the world is a beautiful journey. Yet, it can be frightening or stressful when your baby lags behind others developmentally. However, catching signs of developmental delays early on offers the best hope for improvement, as therapy, including asymmetrical tonic neck exercises and other ATNR-focused interventions, can help.

If your newborn is exhibiting signs of atypical ATNR, consider in-home pediatric therapy from a highly trained occupational or physical therapist. At Kidscare Home Health, we specialize in one-to-one pediatric therapies that take place in the comfort and security of your own on your schedule. We have provided quality, compassionate pediatric home health care to children and families nationwide since 2003.

Contact us today for help or with questions about atypical ATNR interventions!

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What is the purpose of asymmetric tonic neck reflex in babies?

ATNR is part of an infant’s early development and helps them innately explore and interact with their environment before their motor systems develop enough to perform coordinated movements.

What if the asymmetric tonic neck reflex does not disappear?

If the ATNR persists past the typical age of integration (6 to 8 months), it can interfere with coordination and motor development.

What is the asymmetric tonic neck reflex age?

ATNR develops in fetuses while in utero, and its expected integration occurs between 6 months to one year in babies. A retained asymmetrical tonic neck reflex in babies beyond this timeline or an asymmetric tonic neck reflex in adults is atypical.

When does an asymmetrical neck tonic reflex disappear?

Infants typically integrate this reflex between 6 to 8 months in expected developmental timelines.