VT Works

In Part Three, we talked about gravity and the developing relationship between the head, body, and vision. The Tonic Labyrinthine Reflex gave us an opportunity to think about something we normally take for granted: the ability to move our head without the rest of the body being dictated by that position.

With the Asymmetrical Tonic Neck Reflex, or ATNR, we’re going to turn the head again, but this time, something very different happens. Turn a young infant’s head to one side and the arm and leg on the side toward which the face turns tend to extend, while the opposite arm and leg tend toward flexion. The resulting position is sometimes called the “fencing posture.” For the developing infant, this is a normal part of early neurological development. Eventually, though, we need to be able to turn our head without automatically changing what our arms and legs are doing. We need the two sides of the body to cooperate. We need our hands to meet at midline. We need to reach across our body. We need our eyes to look in one direction while our hands do something else. For those of us working in Vision Therapy, perhaps ATNR gives us an opportunity to explore one of the most important developmental relationships of all:

How do the eyes, the hands, and the two sides of the body learn to work together?

What Is the Asymmetrical Tonic Neck Reflex?

The Asymmetrical Tonic Neck Reflex is an early primitive response produced by rotation of the head. When an infant turns the head to one side, the arm and leg on the “face side” tend toward extension while the arm and leg on the opposite, or “skull side,” tend toward flexion. The resulting posture resembles a fencer, which explains the familiar nickname. ATNR is present during early development and is particularly prominent during the first several months after birth. As the nervous system matures, its influence should become increasingly regulated while voluntary movement, postural control, and more sophisticated coordination between the two sides of the body develop. As we discussed with Moro and TLR, regulated may be a more useful word than simply saying that ATNR disappears. In fact, this is one place where the research becomes especially interesting.

Subtle ATNR-like effects have been demonstrated in healthy older children and even healthy adults. Researchers have been able to measure small changes in movement associated with head rotation even when an obvious “fencing posture” isn’t present. That doesn’t mean healthy adults are walking around with a pathological retained ATNR; it simply reminds us that neurological development isn’t necessarily about deleting old circuitry. Instead, higher systems learn to regulate it and prevent an early motor pattern from dictating movement when something more sophisticated is required.

The question, then, may not simply be: “Is ATNR present?”. Perhaps a better question is:

How much influence does head rotation still have over movement when the person is trying to do something else?

ATNR and the Two Sides of the Body

ATNR is inherently asymmetrical: turn the head one way and the two sides of the body respond differently. Early in life, that isn’t necessarily a problem. The infant is beginning to experience relationships among head position, vision, the limbs, and the environment. The hand on the face side enters an area where it can be seen, and movement provides sensory information. In this stage, the infant begins accumulating thousands of experiences connecting what is seen with what is felt and what the body does.

Eventually, however, development requires something more. The two hands need to come together, a toy needs to pass from one hand to the other, one hand needs to stabilize an object while the other manipulates it, the infant needs to reach across the body, and crawling eventually requires coordinated reciprocal movement. Throughout all of this, the head needs to turn without automatically determining what either arm or leg will do, which is where the idea of midline becomes interesting.

We often talk about “crossing midline” as though there were literally a line drawn down the center of the body. There isn’t. What we’re really describing is the nervous system’s increasing ability to coordinate action across the two sides of the body without head position forcing those sides into different patterns. That ability eventually becomes so automatic that most of us never think about it. We reach across the table with whichever hand makes sense, we scratch the opposite shoulder, we turn our head while walking, we hold a piece of paper with one hand while writing with the other, we look to the side while our hands continue doing something directly in front of us. These are relatively simple things.

Until they aren’t.

The Physical Side of a Retained ATNR

If ATNR continues to exert more influence over movement than we would expect, the most obvious place to begin looking is at what happens when the head turns. But once again, a retained ATNR isn’t an explanation for every coordination problem we see. It doesn’t diagnose poor bilateral integration. It doesn’t explain why a child struggles with handwriting. It doesn’t mean that every child who avoids crossing midline has a retained ATNR.

Instead, perhaps it gives us a reason to manipulate one variable and observe what happens. Turn the head and observe what changes. Does an arm want to bend or straighten? Does the shoulder move? Does the trunk rotate with the head? Does balance change? Can the patient maintain the same arm position? Can the hands continue performing a task? Can the patient turn the head while crawling without disrupting the reciprocal movement pattern? Does the response change depending upon which direction the head turns? Those observations made in response to these questions get us much closer to the actual neurological question:

Can the head move independently while the rest of the body continues doing what it was asked to do?

Research in healthy children has found associations between persistent Primitive Reflex activity, including ATNR, and differences in motor performance. Older studies also demonstrated measurable ATNR responses in otherwise typically developing school-age children, reminding us again that the presence of some reflex influence is not necessarily the same thing as pathology. Remember, though, both context and degree matter, but overall function matters as well.

And Then There Is Vision

This may be where ATNR becomes particularly interesting for Vision Therapists. Let’s revisit the infant turning their head resulting in the arm on the face side extending, where it suddenly can be seen. That creates an early opportunity for something extraordinarily important to begin developing:

I see my hand. I feel my hand. I move my hand. Something changes.

Vision and movement begin building a relationship, and eventually that relationship becomes considerably more sophisticated. The eyes have to move independently within the head, the head has to turn independently of the shoulders, the hand needs to move independently of head position, and the eyes need to guide the hand toward something. Sometimes the hand needs to move somewhere other than where the head is pointing. We reach, we grasp, we manipulate, we draw, we write, we catch, we throw, and we use tools. All this is happening while visual information helps guide increasingly precise movement.

ATNR sits at an interesting developmental starting point for that conversation, but this is also where we have to be careful. It is tempting to say that retained ATNR causes poor eye tracking, difficulty crossing visual midline, handwriting problems, reading difficulties, or poor eye-hand coordination, but while those claims are repeated frequently, the evidence does not allow us to make all of those direct causal statements.

There is research associating persistent Primitive Reflexes with motor and cognitive measures, and emerging work examining Primitive Reflex persistence alongside fixation and ocular motility findings. There are also clinical and neurological reasons to be interested in the relationship between head rotation and limb movement, but an interesting developmental mechanism is not the same thing as proven causation. So perhaps we return to what has become a familiar theme in this series:

Observe.

What Happens When the Eyes Cross Midline?

Imagine following a target from left to right. The target crosses the body’s midline, but the eyes don’t encounter a neurological wall when they reach the nose. Ideally, they continue smoothly while the head and body remain appropriately organized for the task. Now imagine reaching for something on the opposite side of the body. Again, there isn’t a literal barrier, but the nervous system does have to coordinate visual information, head position, shoulder and arm movement, proprioception, and the two sides of the body. Now combine the two. Follow something visually while reaching across the body, or maintain fixation straight ahead while turning the head, or keep both arms extended while turning the head from side to side, or maintain a visual task while the hands perform different jobs.

What changes?

Do the eyes hesitate? Does the head follow the eyes unnecessarily? Does the trunk follow the head? Does an arm position change? Does the patient switch hands? Does accuracy deteriorate? Does the task suddenly require much more conscious effort? Again, none of those observations by themselves prove that ATNR caused a visual problem, but they may tell us something very useful about how well visual, proprioceptive, postural, and motor systems are cooperating when the patient crosses from one side of space to the other.

Vision and the Hands

One of the most interesting aspects of ATNR might be that it gives us a natural opportunity to think about the relationship between seeing and doing. As we are mostly aware, vision isn’t simply about identifying something; vision is also about guiding action. Where is it? How far away is it? Can I reach it? How should I orient my hand? How much do I need to move? What happens if the object moves? Did my hand actually go where I thought it went? Visual information helps guide movement, and movement provides new visual information, over and over again. Eventually, the child develops increasingly sophisticated eye-hand behaviors that we tend to take for granted.

Take handwriting, for instance. The eyes are locating a place on the page. One hand is controlling a pencil while the other may be stabilizing the paper. The head has to assume a useful position without dictating what either arm does. The hand moves repeatedly across space while vision monitors accuracy. Posture has to be maintained. Attention has to continue. There is a lot happening. Does that mean retained ATNR causes poor handwriting?

Not even close.

But if a child struggles with a complex visual-motor task like handwriting, and turning the head also produces measurable changes in upper extremity control, that seems like information worth noticing. Again, the reflex doesn’t give us the diagnosis, but it does give us another piece of the puzzle.

What Might This Look Like in the Vision Therapy Room?

As with TLR, we might want to resist creating a list of “ATNR symptoms.” Instead, try changing the demands and watch what happens. Ask the patient to hold both arms forward, turn the head, watch the arms, then give the hands something to do.

Have the patient maintain fixation while turning the head, or even move the eyes while the head remains still. Ask the patient to reach across midline. Use one hand while the other stabilizes. Add balance. Add movement. Add a visually guided motor task. Then increase the complexity.

Does performance change when the head rotates? Does one direction look different from the other? Does the patient compensate by rotating the trunk? Does one arm drift? Does the patient avoid crossing the body? Does visual accuracy change when the motor demand increases? Does a task that was easy suddenly become much harder when the eyes, head, and hands are required to do different things?

Then observe. Once again, the most useful information may not be whether we can elicit ATNR: instead, it may be when ATNR-like influence begins interfering with something the patient is actually trying to accomplish.

What About Reading and Attention?

This is another area where special care is needed.

Primitive Reflex literature contains reported associations with reading, academic performance, attention, and neurodevelopmental conditions. A recent systematic review of persistent Primitive Reflexes found associations with motor and cognitive development, including reading, spelling, and mathematics, but also emphasized that the available literature is limited and heterogeneous. There is also research examining ATNR and STNR in children with ADHD, including a systematic review and meta-analysis reporting an association between tonic neck reflex persistence and ADHD. But remember, association still isn’t a diagnosis. A retained ATNR does not mean a child has ADHD. It doesn’t mean ATNR caused a reading problem, and identifying ATNR doesn’t tell us why a particular student is struggling in school.

The association isn’t necessarily transitive. Similar to Moro and the impacts of emotional dysregulation, just because A is associated with B, and B is associated with C, doesn’t mean we can assume A is associated with C.

What it may do is encourage us to ask whether a visually demanding academic task is also placing unexpected demands on postural and motor organization. Consider reading across a page. The eyes repeatedly move from one side of visual space to the other, the head needs to remain appropriately controlled, and the body maintains posture. Attention has to remain engaged, and the reader has to process language and comprehend what they’re seeing. If some portion of the physical or visual-motor foundation requires more effort than expected, the entire task may become more demanding. But that’s very different from saying: “Retained ATNR causes reading problems”.

The first statement asks a clinical question, while the second claims an answer we don’t have.

What Happens After Brain Injury?

ATNR gives us another interesting question when we consider acquired neurological injury.

In established neurological literature, primitive or tonic reflex influences can become more apparent when higher-level motor control is disrupted. ATNR patterns have been described particularly in neurological conditions involving significant motor-system injury. There is also evidence that subtle ATNR effects can be measured in neurologically intact adults, which makes the question of “re-emergence” more nuanced than simply imagining a reflex disappearing during infancy and suddenly switching back on after injury.

With concussion and other forms of traumatic brain injury, we know that patients may develop problems involving eye movements, convergence, accommodation, visual-vestibular integration, balance, postural control, coordination, attention, and sensory tolerance. However, what is much less established is whether a mild traumatic brain injury routinely causes a developmental ATNR to “come back.” Again, the evidence does not allow us to say that.

Perhaps the more interesting question is:

Has the injury reduced the nervous system’s ability to keep an underlying motor pattern appropriately regulated while the patient performs more sophisticated movement?

If turning the head after brain injury changes arm position, balance, gait, visual performance, or coordination, that’s worth observing. If maintaining fixation while turning the head becomes difficult, that’s worth observing. If the patient can perform an eye-hand task sitting still but loses accuracy when head rotation or movement is introduced, that’s worth observing. Not because any one of those findings proves that ATNR returned, but because they may tell us something about how well the nervous system is coordinating systems that previously worked together automatically.

What Does the Research Actually Tell Us?

Once again, this is where we need to separate what we know from what we suspect. We know that ATNR is a normal early neurological response in which head rotation influences limb posture, producing extension on the face side and flexion on the opposite side. We know that its influence normally becomes increasingly regulated as voluntary movement and postural control mature. We know that ATNR-like effects can still be measured in some healthy older children and adults, which reminds us that regulation is more complicated than simply saying the reflex has vanished.

Research has found associations between persistent Primitive Reflex activity, including ATNR, and differences in motor performance. Research has also examined associations between tonic neck reflex persistence and ADHD, and more broadly between persistent Primitive Reflexes and aspects of cognitive and academic performance. Emerging research has examined relationships between Primitive Reflex persistence and ocular-motor findings, and neurological injury can be associated with disinhibition or increased expression of primitive motor patterns.

We do not currently have sufficient evidence to say:

• Retained ATNR causes a particular binocular vision disorder
• Retained ATNR causes poor eye tracking
• Retained ATNR causes dyslexia or a reading disorder
• Retained ATNR causes ADHD
• Retained ATNR causes handwriting problems
• Integrating ATNR will treat any of those conditions
• A concussion routinely causes developmental ATNR to return

Those are considerably stronger statements than the evidence supports, and just as we’ve seen with Moro and TLR, refusing to make those leaps doesn’t make ATNR less interesting. It actually makes the observations more meaningful.

What Should the Vision Therapist Take Away?

Perhaps ATNR gives us one of the clearest examples yet of why Primitive Reflexes should never be considered in isolation. Turning the head involves the neck, but it can also influence posture. It changes what the eyes see, and it changes the relationship between the body and the environment. The arms and hands may be involved. Balance may be involved. Eye-hand coordination may be involved. When the patient is performing a real-world task, all of those systems have to cooperate.

So perhaps instead of simply asking:

“Does this patient have a retained ATNR?”, we just observe.

What happens when the head turns? What happens to the arms? What happens to posture? Can the eyes move without the head? Can the head move without changing what the hands are doing? Can the patient reach across the body? Can one hand work independently while the other stabilizes? Can the patient maintain visual accuracy while movement becomes more complicated? How much effort does all of that require?

Because ultimately, the goal isn’t simply to make a reflex test negative; instead, the goal is increasingly flexible movement. The head should be able to turn while the hands continue their job. The eyes should be able to cross from one side of space to the other. The hands should be able to work together or independently. One side of the body should be able to cooperate with the other without being dictated by where the face happens to be pointing, and vision should be able to guide all of it.

A retained ATNR is not a diagnosis. It doesn’t explain every reading, writing, coordination, or attention problem we see. It’s just another observation, another piece of information. Perhaps it is also another opportunity to understand how the person sitting in front of us has learned to connect seeing with doing.

Stay tuned for Part Five: the Symmetrical Tonic Neck Reflex (STNR) and the developing relationship between the upper and lower body, posture, and near vision.

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