The Asymmetrical Tonic Neck Reflex (ATNR) is an involuntary movement pattern observed in infants, considered one of the primitive reflexes present from birth. This reflex is a fundamental part of early brain development, helping a baby interact with their environment before purposeful movements develop. It is sometimes referred to as the “fencer’s pose” due to the distinct posture an infant assumes when activated. The ATNR is an automatic response originating in the brainstem, indicating nervous system function and supporting early development.
How the Reflex Manifests
The ATNR is triggered when an infant’s head is turned to one side. The arm and leg on the same side extend or straighten. Simultaneously, the limbs on the opposite side will flex or bend inward, creating a distinctive posture. For example, if a baby’s head is turned to the right, their right arm and leg will extend, while their left arm and leg will bend.
Infants often display this reflex when lying on their back. Observing this reflex helps professionals assess the healthy functioning of a baby’s central nervous system.
Typical Developmental Progression
The Asymmetrical Tonic Neck Reflex begins developing as early as 13 to 18 weeks into pregnancy and is fully present at birth. It plays a role in the birthing process. This primitive reflex is expected to naturally integrate, or disappear, as the infant’s brain matures and more voluntary motor skills develop.
The ATNR should integrate between 5 to 7 months of age, though it can sometimes take up to 9 to 12 months for full integration. Integration signifies that the reflex no longer dictates limb movement, and the baby begins to make intentional, coordinated actions. The presence of the ATNR beyond this expected timeframe is considered atypical development.
Why This Reflex Matters
The ATNR serves several important purposes in early infant development. It is involved in developing hand-eye coordination, influencing a baby’s ability to reach out and explore their surroundings. This reflex also contributes to muscle tone and the development of the vestibular system, which is connected to balance and spatial orientation.
The ATNR promotes unilateral movement patterns, which are foundational for later bilateral coordination. It prepares the infant for more complex movements such as rolling, creeping, and crawling. The reflex also influences visual skills, including depth perception, visual fixation, and tracking moving objects.
When the Reflex is Atypical
When the Asymmetrical Tonic Neck Reflex does not integrate within the typical timeframe, it is referred to as a “retained ATNR.” This persistence can indicate an underlying issue and affect a child’s ongoing development. Factors contributing to a retained ATNR include a traumatic birth process, C-section delivery, insufficient tummy time in infancy, or chronic ear infections.
A retained ATNR can lead to various developmental challenges. Children might exhibit difficulties with balance, especially when moving their head from side to side. It can interfere with visual tracking, making it hard to follow a line of text or focus from near to far, potentially impacting reading, spelling, and writing abilities. Challenges with fine motor skills, such as handwriting difficulties or an excessively tight grip on utensils, are also observed. These children may also struggle with tasks requiring both sides of the body to work together, like catching a ball or riding a bicycle. If there are concerns about a child’s developmental progress, consulting a pediatrician or developmental specialist is recommended.