The tonic neck reflex, also known as the asymmetrical tonic neck reflex (ATNR), is an involuntary, automatic response present at birth. It is one of several primitive reflexes that indicate a baby’s healthy nervous system development. This reflex is a temporary and expected phase in an infant’s initial months of life.
Understanding the Reflex
The tonic neck reflex is often called the “fencing pose” or “fencing reflex” due to the posture a baby assumes. It is observed when an infant is lying on their back and their head is gently turned to one side. As the head turns, the arm and leg on the side the face is pointing towards will extend.
Simultaneously, the arm and leg on the opposite side of the body will flex. For instance, if a baby’s head turns to the right, the right arm and leg will extend, while the left arm and leg will bend. This creates an asymmetrical body alignment.
The reflex is subtle and best observed when the baby is calm. Pediatricians routinely check for it to assess neurological function. Parents can also observe it at home by gently turning their baby’s head while they are lying down.
The Purpose of the Reflex
The tonic neck reflex serves several functions in early motor and sensory development. It develops in the womb, assisting the baby during birth.
After birth, the reflex contributes to hand-eye coordination. As the head turns and the arm extends, it helps infants discover their hands, track objects visually, and prepares them for voluntary movements like reaching and grasping.
The reflex also establishes body awareness and helps break up symmetrical movement patterns. This prepares infants for later, more complex motor skills like rolling over and crawling, which require independent movement of body sides. It also aids in muscle tone development and helps the baby learn to orient themselves in space.
Normal Development and Persistence
The tonic neck reflex is present at birth and integrates, or disappears, as higher brain centers mature. This integration usually occurs between 4 to 7 months of age. Its fading allows for the emergence of more voluntary and coordinated movements.
If the tonic neck reflex persists beyond 7 months, it can indicate developmental delays or neurological considerations. A retained reflex may interfere with advanced motor skills, hindering a child’s ability to roll, bring hands to the midline, or develop proper balance and coordination.
Children with a persistent ATNR can experience difficulties with hand-eye coordination, visual tracking, or crossing the body’s midline. These challenges can affect activities such as writing, reading, and engaging in sports. If there are concerns about the persistence of this or any other primitive reflex, consulting a healthcare professional is advisable for proper evaluation and guidance.