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In Part Four, we explored the Asymmetrical Tonic Neck Reflex and the developing relationship between the eyes, the hands, and the two sides of the body. ATNR gave us an opportunity to think about what happens when the head turns and how the nervous system eventually learns to keep that movement from automatically dictating what the arms and legs will do.

With the Symmetrical Tonic Neck Reflex, or STNR, we’re going to move the head again, but this time, instead of turning it from side to side, we’re going to look up and down, and observe as something interesting happens.

When the head moves upward into extension, the arms tend toward extension while the legs tend toward flexion. When the head moves downward into flexion, the relationship reverses: the arms tend toward flexion while the legs tend toward extension. For the developing infant, this relationship between the head, upper body, and lower body may help support an important transition toward quadruped movement and crawling. Eventually, though, we need something much more sophisticated.

We need to be able to look down without our arms collapsing beneath us. We need to look up without our lower body automatically changing position. We need the upper and lower portions of the body to cooperate, but we also need them to operate independently when the task demands it. And for those of us working in Vision Therapy, STNR raises an especially interesting question:

What happens when looking changes what the rest of the body wants to do?

What Is the Symmetrical Tonic Neck Reflex?

The Symmetrical Tonic Neck Reflex is a developmental motor response associated with flexion and extension of the head and neck. Unlike ATNR, which creates different responses on the two sides of the body, STNR creates a relationship between the upper and lower portions of the body.

Head up: the arms tend toward extension and the legs toward flexion.

Head down: the arms tend toward flexion and the legs toward extension.

This pattern becomes particularly interesting when the infant begins spending more time on hands and knees. Now the nervous system has to coordinate the head, arms, trunk, hips, and legs while maintaining the body against gravity. Movement of the head changes the demands placed on the rest of the system. STNR is often described as appearing later than many of the primitive reflexes and becoming increasingly regulated during the first year of life. As with the other reflexes we’ve discussed, however, exact developmental timelines should probably be treated with some humility. Studies of typically developing infants have not always found STNR at the same ages or with the same frequency.

That shouldn’t be terribly surprising since development rarely reads the textbook. Perhaps, once again, the more useful concept isn’t that STNR simply “disappears.” The nervous system becomes increasingly capable of moving the head without requiring the upper and lower body to follow an obligatory pattern. Similar to what we discussed with ATNR, subtle STNR-like effects can still be measured in healthy adults. So maybe the question isn’t simply “Is STNR present?”

Perhaps the better question is:

How much influence does looking up or down still have over what the rest of the body is trying to do?

Separating the Upper and Lower Body

STNR gives us an interesting way to think about something most of us rarely consider: the upper and lower body have to learn how to work together without always doing the same thing.

Consider an infant on hands and knees where the arms are supporting the upper body while the hips and legs are supporting and eventually propelling the lower body. The head needs to move so the infant can look around. Weight has to shift from one limb to another. Eventually, one arm has to leave the floor while the opposite leg moves. That’s a lot of organization as crawling is not simply four limbs moving. Crawling requires changing weight distribution, postural control, reciprocal movement, sensory feedback, head control, and an ongoing relationship with gravity and the visual environment. STNR sits right in the middle of that conversation.

If looking down encourages the arms to flex while the legs extend, and looking up encourages the opposite pattern, then development eventually requires the nervous system to become less controlled by that relationship. The infant has to develop better options, and perhaps that’s a useful way to think about integration: the nervous system develops better options.

The Physical Side of a Retained STNR

If STNR continues to exert more influence over movement than expected, head flexion and extension give us a fairly simple variable to manipulate.

Look up. What changes?

Look down. What changes?

Do the elbows bend? Do the arms straighten? Does the pelvis shift? Do the knees change position? Does the trunk move? Does balance change? Can the patient maintain the same posture while the head moves? Put the patient on hands and knees and the relationship may become even more interesting. Can the patient maintain quadruped while looking up and down? Does the body rock forward or backward? Do the elbows repeatedly unlock? Does the patient sit back toward the heels? Does the pelvis rise? Does the trunk lose its organization?

Then change the task. Ask the patient to reach for something while maintaining quadruped. Add reciprocal movement. Add visual fixation. Move the target. Ask the patient to look somewhere different from where the hands are working. Again, none of these observations by themselves diagnose a retained STNR or explain a coordination problem. They simply let us ask a neurological question:

Can the head change position while the upper and lower body continue doing what the task requires?

Research examining persistent Primitive Reflex activity, including STNR, has found associations with differences in motor performance in preschool children, but as we’ve discussed throughout this series, association doesn’t tell us that STNR caused the motor difficulty, and the presence of some reflex influence does not automatically make it pathological.

Context matters. Degree matters. Overall function matters.

And Then We Sit at a Desk

This may be where STNR becomes especially interesting for Vision Therapists, since eventually, most children stop spending their days crawling around on hands and knees. They sit at a desk, and we ask them to look down – a lot. They look down at a book, they look down at handwriting, they look down at worksheets, they look down at a tablet, they look back up at a teacher or a board and then back down to the desk. Over and over again.

Of course, looking down at a page is not the same neurological task as flexing the head while maintaining quadruped, and we should be very careful about making that leap, but the developmental question is interesting. Can the head move into a useful position for near work while the shoulders, arms, trunk, and lower body remain appropriately organized? For most of us, the answer is yes, and we never give it another thought.

Until it isn’t. Same as ATNR.

Posture and Near Vision

Near vision is often discussed in terms of accommodation, convergence, fixation, pursuits, saccades, and binocular coordination, and those systems matter enormously, but the eyes don’t arrive at the desk by themselves. They arrive attached to a head, the head is attached to a neck, the neck sits on a trunk, and the trunk sits over a pelvis. Somehow, the entire system has to remain organized while the eyes perform a highly demanding visual task. A child reading or writing at a desk has to maintain a workable head position, support the trunk against gravity, stabilize the shoulders sufficiently for the hands to work, maintain balance in sitting, and repeatedly move the eyes through near space.

That doesn’t mean STNR causes poor posture, nor does it mean retained STNR causes convergence insufficiency. It also doesn’t mean STNR explains why a child lies across the desk, hooks a leg around the chair, props the head on a hand, or constantly changes position, but if changing head position reliably changes postural organization, that seems like information worth noticing. Once again, the plan is unchanged:

Observe.

What Happens When We Look Up and Down?

Try changing one thing.

Have the patient sit comfortably and maintain fixation on a near target, then move the target lower. What changes? Bring it higher, observe what changes. Have the patient maintain the same arm position while looking up and down.

Ask them to perform a fine-motor task while changing gaze between near and far. Have them read something on the desk, then look at something across the room, then return to the page. What occurs if we add balance or movement? What happens to the head? What happens to the shoulders? What happens to the trunk? Does the patient move the entire body to follow the visual target? Does accuracy change? Does the task require more effort? Does posture gradually collapse as the visual demand continues?

None of those findings prove that STNR caused a visual problem, but they may tell us something important about how well vision, head position, posture, proprioception, and movement are cooperating.

Vision Is Part of Posture

One of the recurring themes in this series is that vision isn’t something that happens independently from the rest of the body. Vision helps organize movement, movement changes visual information, posture changes where the eyes are in space, and where the eyes are directed can change what the body needs to do. STNR just gives us another way to explore that relationship.

Imagine looking down to thread a needle, tie a shoe, write your name, build something with small blocks, or read a paragraph. The visual system has one job while the hands may have another. The head has to find a useful position, and the body has to support all of it. As the task becomes more complicated, the nervous system has to allow those systems to cooperate without requiring them to move as one unit. That’s a very different idea from saying:

“Retained STNR causes a near vision problem.”

We don’t have evidence to make that statement. What we can say is that visual tasks occur within a postural and motor system, and STNR gives us one possible window into how independently those systems can operate.

What Might This Look Like in the Vision Therapy Room?

As with Moro, TLR, and ATNR, a checklist of “STNR symptoms” might not be the most advantageous. Instead, manipulate the relationship. Change head position, change posture, change the visual demand, change what the hands are doing.

Then observe.

Can the patient maintain quadruped while moving the head? Can the arms and legs maintain their jobs? Can the patient reach without losing the posture? Can the eyes move without requiring the entire head and trunk to follow? Can the patient look down while the upper body remains stable? Can the patient move repeatedly between near and far without reorganizing the entire body each time?

Then increase complexity. Add a metronome, add balance, add a cognitive task, add a second visual target, add movement. The question isn’t whether the patient looks perfect.

The question is: at what point does the system stop being flexible?

That may be much more useful than simply assigning a reflex score.

What About Reading and Attention?

This is another place where STNR is often given more explanatory power than the research supports. Persistent Primitive Reflexes have been studied in relation to motor performance, learning, academic skills, and attention. A recent systematic review found reported relationships between persistent Primitive Reflexes and aspects of motor and cognitive development, including reading, spelling, and mathematics, while also emphasizing the limited and heterogeneous nature of the literature.

STNR has also been specifically examined in relation to ADHD. A 2023 systematic review and meta-analysis found a moderate association between STNR persistence and ADHD, but the authors themselves emphasized that research in this area is still in its early stages and that longitudinal or experimental research is needed to establish causation.

So once again:

A retained STNR does not diagnose ADHD. It doesn’t explain why a child cannot pay attention. It doesn’t mean STNR caused a reading problem. It doesn’t mean that “integrating STNR” will treat ADHD or a learning disorder.

Association still isn’t causation.

Perhaps what the observation can do is make us curious about the amount of effort required to maintain the physical foundation beneath a visual and cognitive task. If sitting upright, stabilizing the head, maintaining the shoulders, controlling the hands, and looking repeatedly across near space require more effort than expected, could that make a demanding academic task harder? Perhaps.

But that’s a question. Not an answer.

What About the Visual System Itself?

There is emerging research examining Primitive Reflex persistence alongside fixation and ocular-motility measures. A 2024 study examined ATNR, STNR, TLR, and Moro in relation to several eye-movement variables and reported changes in fixation and ocular-motility measures following an intervention intended to inhibit those reflexes.

That’s interesting, but it should not be turned into more than it is. The study does not establish that retained STNR causes an ocular motor disorder, nor does it establish that STNR integration is a proven treatment for a specific binocular vision diagnosis. It does give researchers, and perhaps clinicians, a reason to continue asking questions about relationships among motor development, posture, Primitive Reflex activity, and ocular motor function. And that’s exactly where we should leave it.

Interested. Curious. Careful.

What Happens After Brain Injury?

STNR also gives us an interesting way to think about the patient after concussion or other acquired brain injury. We already know that traumatic brain injury can disrupt systems involving eye movements, convergence, accommodation, vestibulo-ocular function, balance, postural control, attention, and sensory tolerance. What we do not know is that concussion routinely causes a developmental STNR to suddenly “come back.” As we saw with ATNR, that may be an oversimplified way of thinking about the nervous system. Subtle STNR effects have been demonstrated even in healthy adults. In neurological injury, primitive or tonic motor influences may become more apparent when higher-level motor regulation is disrupted. So perhaps the better question after brain injury isn’t: “Did the concussion bring STNR back?”

Perhaps it is:

Has the injury changed the nervous system’s ability to keep head movement, posture, vision, and limb control appropriately independent while they are being used together?

Have the patient move the head while maintaining posture. Change visual distance. Add balance. Add upper-extremity movement. Move from sitting to standing. Try a visual task while the body is moving. If performance changes dramatically as systems are combined, that is useful information. It still doesn’t prove that STNR “returned.” It tells us that a nervous system that once coordinated multiple demands automatically may now be working much harder to do so.

And that distinction matters.

What Does the Research Actually Tell Us?

Once again, this is where we separate what we know from what we suspect. We know that STNR is a developmental motor response involving a relationship between head flexion and extension and upper- and lower-extremity posture. We know that measurable STNR-like effects can still be demonstrated in healthy adults. Research has reported associations between persistent Primitive Reflex activity, including STNR, and differences in motor performance in children.

Research has also examined STNR in relation to ADHD and other developmental outcomes, although causation has not been established and the overall evidence remains limited. Emerging research has examined Primitive Reflex persistence in relation to ocular-motor findings, while we have substantial evidence that concussion and traumatic brain injury can disrupt visual, vestibular, balance, and postural systems.

What we do not currently have sufficient evidence to say is:

• Retained STNR causes convergence insufficiency
• Retained STNR causes accommodative dysfunction
• Retained STNR causes poor eye tracking
• Retained STNR causes poor posture
• Retained STNR causes reading difficulties or dyslexia
• Retained STNR causes ADHD
• Retained STNR causes handwriting problems
• Integrating STNR will treat any of those conditions
• Concussion routinely causes developmental STNR to return

Those statements move far beyond what the evidence currently supports. Once again, refusing to make those claims doesn’t make STNR less interesting.

Hopefully, it makes us better observers.

What Should the Vision Therapist Take Away?

Perhaps STNR gives us another opportunity to think about something that seems incredibly simple once the nervous system has learned how to do it.

Look up. Look down. Keep doing everything else.

The head should be able to change position without automatically determining what the arms and legs do. The upper and lower body should be able to cooperate without being locked together. The hands should be able to perform one task while the eyes perform another. The body should be able to maintain a useful posture while vision moves through space, and when the task changes, the nervous system should have options.

That’s really what we’re looking for – options.

Can the patient look down without the whole body collapsing into the movement? Can they look up without losing what the hands are doing? Can they move from near to far? Can they maintain posture while the visual demand increases? Can they combine movement, vision, balance, and cognition without one system taking over everything else?

A retained STNR is not a diagnosis. It doesn’t explain every postural, visual, reading, coordination, or attention problem we see. It’s another observation – another piece of information. Perhaps it is also another opportunity to understand how the person sitting in front of us learned to separate movement that once belonged together, so those same movements could eventually work together in far more sophisticated ways.

Stay tuned for Part Six: the Spinal Galant Reflex and the developing relationship between the trunk, movement, and the space around us.

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