Primitive reflexes are a set of automatic, involuntary movements designed to aid infant survival and motor development. Originating in the brainstem, these reflexes should naturally transition into voluntary movements as the nervous system matures. The Symmetric Tonic Neck Reflex (STNR) helps bridge the gap between lying down and achieving the four-point position necessary for crawling. If this pattern remains active past its typical timeline, it can affect motor skills and learning in older children, necessitating a simple screening test.
The Symmetric Tonic Neck Reflex Explained
The Symmetric Tonic Neck Reflex, or STNR, is a temporary motor pattern that typically appears between six and nine months of age. Its primary function is to help an infant overcome the effects of gravity and rise up onto their hands and knees, establishing the quadruped position. This reflex facilitates the separation of movement between the upper and lower halves of the body.
The reflex is characterized by two distinct actions linked to head movement. When the infant’s head tips down toward the chest, the arms will naturally bend while the legs straighten. Conversely, when the head lifts and tips back, the arms straighten, and the legs bend. This pattern helps the baby engage in the rocking motion that precedes hands-and-knees crawling. The STNR is considered integrated, or no longer active, by around 9 to 12 months of age, allowing for coordinated, independent limb movement. If the reflex is still present beyond this window, it may interfere with more complex motor and visual skills.
Indicators That STNR May Be Active
When the STNR remains unintegrated in an older child, the involuntary movement pattern can manifest as several observable physical and behavioral difficulties. One common sign is a slumped or poor posture, especially when sitting at a desk or table, because maintaining a straight back may activate the reflex. The child may seem to struggle against their own body, leading to constant fidgeting or an inability to sit still comfortably in a chair.
Visual tracking difficulties are also frequently associated with a retained STNR, particularly when copying information from a whiteboard or blackboard to a paper on the desk. The repeated head movement required to look up and then down can trigger the reflex, causing involuntary tension or movement in the arms, which disrupts the task. Other physical indicators include:
- Poor hand-eye coordination.
- A perceived clumsiness.
- A tendency to sit in a “W” position on the floor, which provides greater stability by locking the legs.
- Difficulties with swimming, particularly synchronizing arm and leg movements.
Step-by-Step STNR Testing Procedure
A preliminary screening for a retained STNR can be performed safely at home by a parent. Begin by having the child remove their shoes and kneel on a soft, flat surface, such as a carpet or mat. Instruct the child to assume the quadruped, or “all fours,” position, with their hands directly under their shoulders and their knees under their hips, forming a tabletop shape.
The child should keep their arms straight and their back flat, ensuring their head is in a neutral position, looking at the floor slightly in front of their hands. This starting position establishes a baseline posture before the movement begins. You will then guide the child through two distinct head movements, observing their arms and legs for any involuntary shifts in muscle tone or position.
For the first movement, instruct the child to slowly and fully tuck their chin to their chest, looking backward towards their belly button. They should hold this head-down position for approximately five seconds while maintaining the tabletop shape. Closely watch the child’s arms for any tendency to bend or flex at the elbows, and their legs for any tendency to straighten or push back.
Next, instruct the child to slowly lift their head and look straight up toward the ceiling, extending their neck fully and holding this head-up position for five seconds. During this movement, observe the child’s arms for any involuntary tendency to straighten or lock the elbows, and their legs for any bending or flexing at the knee. Repeat the full sequence of head-down and head-up movements three times for a reliable observation.
Interpreting Test Outcomes
Interpreting the results of this at-home screening involves comparing the observed movements to the expected pattern of an active reflex. A positive result, indicating that the STNR may be retained, occurs if the child exhibits the involuntary limb movements. Specifically, the reflex is active if the arms bend when the head is tucked down, or if the legs bend when the head is lifted up.
A retained reflex is also suggested if the child loses their balance, shifts their weight backward toward their heels, or is unable to maintain the starting position without significant effort or wobbling during the head movements. These reactions show that the brainstem-controlled reflex is overriding the child’s voluntary motor control. Conversely, a negative result, indicating the reflex is likely integrated, is observed if the child maintains a smooth, stable tabletop position throughout both the head-down and head-up movements, with no involuntary bending or straightening of the arms or legs. The child’s movement should be fluid and controlled. If this simple screen suggests the reflex is still active, it is recommended to consult with a qualified professional, such as an occupational therapist, physical therapist, or developmental pediatrician. This at-home screening is a tool for preliminary observation, not a formal medical diagnosis.