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Possible indicators of a retained Asymmetrical Tonic Neck Reflex:

- Difficult, prolonged birth, or unusually quick delivery
- Overall lack of muscle tone, or tension in the neck and shoulders
- Poor sense of left and right, and/or mixed laterality: eg left handed but right footed
- Difficulty coordinating the two sides of the body: runs or walks with an unusual gait, trouble with swimming (especially front crawl)
- Clumsy, poor balance
- Poor hand-eye coordination
- Underdeveloped fine motor skills
- Poor visual skills (especially eye tracking and convergence)
- Struggles with fluent reading or writing: person may express themselves much better verbally than they can in their written work, or they may find reading or writing very tiring

What is the
Asymmetrical Tonic Neck Reflex (ATNR)?

The Asymmetrical Tonic Neck Reflex (ATNR) is a primitive reflex found in pre-birth (from about 18 weeks gestation) and new-born babies.  When the baby's head is turned to one side, the ATNR will cause the limbs on that side to stretch out, whilst the limbs to the other side bend.  If the head is then turned the other way, the pattern in the limbs changes accordingly.  This movement is thought to play a role in the birth process: to pass through the pelvis of the mother during birth involves rotation of the head of the baby.  The resultant asymmetric flexion and extension of the limbs due to the ATNR will then help the shoulders to pass the through the pelvis also.

Both in utero and post-birth, the ATNR plays important roles in development:

- It stimulates the development of muscle tone in the baby: movements of the head cause movement in all limbs, and thus the baby is constantly obliged to use its developing limb muscles, which grow stronger as a result.  This will be crucial if the tiny baby is to develop is the physical strength to develop independent movement later on. 

- It provides essential stimulation to the inner ear of the foetus as it moves around in utero, and neural connections to the inner ear begin to be made, helping the very early development of the vestibular system (which will be responsible for balance and play a large role in sensory integration).

- Through the asymmetric movement resulting from the ATNR, the infant starts to develop a sense of physical midline.  The human brain is divided into two halves, the midline between them extending to divide the whole body into left and right.  Awareness of this midline is essential to the individual’s sense of proprioception (of where the various parts of the body are at any time), and to the ability to execute coordinated movement.  A strongly developed physical midline is also crucial to the action of the vestibular system, allowing the infant to orientate itself in response to gravity.  

- The ATNR helps the baby to develop a wider sense of physical self in its early months.  No matter which way the baby turns its head, the ATNR will ensure that a hand is visible in the near field.  A link between eyes and hand thus starts to develop, as the baby slowly becomes aware that its hand is part of itself. 

What happens if the ATNR is retained?

As one of a number of primitive reflexes, the ATNR should not remain active into childhood: having done its job, it should be inhibited by the time the infant is roughly 6 months old, as it achieves voluntary limb control. 

If the ATNR does not inhibit, the infant is likely to have a poor sense of their own physical midline.  Integration and coordination of the left and the right sides of the body can be compromised.  As such, the first sign of a retained ATNR is often that the infant doesn’t learn to crawl properly at the usual time: it is very difficult to crawl with the usual cross pattern of movement if coordination between the two sides of the body is compromised.  These infants will still attain mobility through “bum shuffling” or other adaptations of the crawling pattern, and thus the interruption in their development will often not be noticed.  However, crawling is an important milestone as it provides important feedback to the vestibular system, beginning the integration of information from the senses of balance, proprioception, and vision.  A child who never crawls may thus have difficulty developing good hand-eye coordination and may have poor visual perception skills.

Other issues resulting from a poorly developed sense of physical midline may also trouble a child with a retained ATNR.  This child will have real difficulty mastering actions that require them to cross their midline or coordinate their two sides.  For instance, they may appear clumsy when trying to pass an object from one hand to the other; they may not fully develop laterality; they may have difficulty reading or writing as their eyes cannot fluently track through the midline.  In addition, they may have difficulty with walking or running, and find this very tiring, or they may be poor at swimming, particularly in executing front crawl: these issues may be exacerbated by the poorly developed muscle tone that can result from a retained ATNR.

The child may well overcome some or all of these issues: for instance, mobility will be adequate, and the child will be able to read and write eventually.  However, these tasks will require supreme effort, and therefore multitasking (e.g. thinking while writing) becomes very difficult.  The child is often observed to struggle generally at school, or may suffer specific difficulties, for instance the teacher notices a mismatch between their verbal and written abilities. An ATNR child has to work much harder to learn in a school environment than most of their peers.