Primitive reflexes are involuntary movement patterns that are present at birth, serving as the body’s earliest responses to specific stimuli. These reflexes are programmed into the central nervous system to help with survival and early motor development. The Asymmetrical Tonic Neck Reflex (ATNR), often called the “fencing posture,” is one such automatic movement pattern. For higher-level motor skills and voluntary movement to develop, these primitive reflexes must eventually fade away, or “integrate,” as the nervous system matures.
What Exactly is the ATNR Reflex?
The Asymmetrical Tonic Neck Reflex is a movement pattern that connects the head, eyes, and limbs, creating an automatic, temporary link between them. This reflex is triggered by turning the infant’s head to one side while the baby is lying on their back. When the head turns, the limbs on the side the face is pointing towards will extend, while the limbs on the opposite side will flex or bend. This characteristic posture is why the ATNR is commonly referred to as the “fencing reflex” or “bow and arrow reflex.”
This reflex begins developing quite early, often observed around 18 weeks while the fetus is in utero. In utero, the ATNR contributes to the development of muscle tone and stimulates the vestibular system. After birth, it is believed to help the baby move through the birth canal during delivery. The reflex also plays a role in training the infant’s hand-eye coordination by repeatedly bringing the extended hand into the field of vision.
The ATNR also promotes awareness of the two sides of the body and assists in developing unilateral movement. However, the involuntary nature of the reflex means that the head movement dictates the movement of the limbs. For a baby to reach and grasp an object intentionally, this primitive link must eventually be broken.
The Typical Timeline for Reflex Integration
The ATNR is present at birth and should begin to diminish as the infant grows and gains more purposeful motor control. The expected window for the reflex to disappear is between four and seven months of age. Most often, the reflex is no longer consistently observable by the time a baby reaches six months old. This integration is a sign that the infant’s nervous system is developing as expected and that lower brain centers are yielding control to higher brain functions.
Integration is necessary because the ATNR prevents the baby from performing movements that cross the body’s midline, such as bringing both hands together to grasp a toy. If the reflex remains dominant, every time the baby turns their head, the automatic limb extension makes voluntary, coordinated movement difficult. The fading of the ATNR allows the infant to achieve milestones like rolling over, bringing their hands to their mouth, and eventually pushing up onto their hands and knees for crawling.
The persistence of the ATNR past approximately seven months of age may warrant observation by a healthcare professional. The inability to move the limbs independently of head movement can impede the development of core stability and bilateral coordination, which are necessary for complex motor skills.
Recognizing a Retained ATNR
When the Asymmetrical Tonic Neck Reflex does not integrate within the expected timeframe, it is considered “retained.” The presence of a retained ATNR can interfere with a child’s subsequent motor and learning skills because head movements continue to trigger subtle, reflexive limb movements.
Effects on Motor and Academic Skills
A retained ATNR often manifests in several ways, including difficulty with activities that require crossing the midline of the body, such as touching the left knee with the right hand. This is because the reflex’s pattern of extension on the face side and flexion on the skull side makes it challenging to bring a limb across the body’s center line.
In the classroom, the reflex affects fine motor skills, particularly handwriting. When a child looks down to write, the head turn can subtly trigger the reflex, causing the writing arm to extend or stiffen. This often results in a messy handwriting style, an overly tight grip on the pencil, or the need to write with the paper turned at an extreme angle.
Other indicators of a retained ATNR include:
- Struggles with bilateral coordination, often seen in activities like riding a bicycle or catching a ball.
- Difficulty with visual tracking, such as following words across a page while reading.
- Poor balance when running or jumping.
- Difficulty establishing a consistent hand dominance past the age of seven.
- Challenges with sustained focus and attention during tasks that involve looking from a board to a desk.