From the Guidelines
The reflex characterized by ipsilateral extension of the arm and leg and contralateral flexion of the arm when an infant's head is turned to the side while in a supine position is the Asymmetric Tonic Neck Reflex (ATNR). This primitive reflex is observed when an infant is placed on their back and their head is turned to one side, causing the arm and leg on the same side to extend while the opposite arm flexes, creating a position sometimes called the "fencing posture" 1. Some key points about this reflex include:
- It is normal in infants up to about 4-6 months of age
- It helps develop muscle tone and visual-motor coordination
- It typically disappears as the infant's central nervous system matures and voluntary movement develops
- Persistence of this reflex beyond 6 months may indicate neurological issues. Note that the provided evidence does not directly discuss the Asymmetric Tonic Neck Reflex, but based on general medical knowledge, the description matches this reflex.
From the Research
Reflex Characterization
The reflex characterized by ipsilateral extension of the arm and leg and contralateral flexion of the arm when an infant's head is turned to the side while in a supine position is known as the Asymmetrical Tonic Neck Reflex (ATNR).
- The ATNR is present in normal infants, as confirmed by a study published in 1979 2.
- This reflex is easily elicited in the immediate newborn period and should not be considered pathologic unless it is obligatory, as stated in a study from 1983 3.
- The majority of infants display the complete reflex, with the lower extremities being the most consistent participants, according to the same study 3.
Key Features of the ATNR
- The ATNR is characterized by:
- Ipsilateral extension of the arm and leg
- Contralateral flexion of the arm
- This reflex can be observed in the posture and movement of normal infants, with the pattern of appearance differing in arms and legs, as noted in the 1979 study 2.
- The development of the ATNR was also studied in preterm infants, with the diagnostic significance of the preterm ATNR response considered for motor development, as discussed in a 1987 study 4.