What is the Moro reflex?

From the Guidelines

The Moro reflex is a normal, primitive reflex seen in newborn infants, characterized by a distinctive sequence of arm and leg movements in response to a startling stimulus, as evidenced by its mention in the context of neurologic excitability in neonatal narcotic abstinence syndrome 1. The Moro reflex is typically triggered by a loud noise, sudden movement, or loss of support, causing the infant to throw their arms outward with palms up and fingers spread, followed by bringing the arms back to the center of the body in an embracing motion. This reflex is often accompanied by crying and may include leg extension. Some key features of the Moro reflex include:

• Arm extension and abduction with palms up and fingers spread
• Followed by arm adduction and flexion, often with a crying response
• May be accompanied by leg extension
• Typically disappears by 3-6 months of age
• Serves as an important neurological marker during infant development, indicating proper brain and nervous system functioning, as seen in the context of neonatal drug withdrawal, where an exaggerated Moro reflex is a clinical feature of neurologic excitability 1. Healthcare providers routinely check for this reflex during newborn examinations and well-baby visits to assess neurological development. Persistence of the Moro reflex beyond 6 months may indicate potential neurological issues and should be evaluated by a healthcare provider. In the context of neonatal narcotic abstinence syndrome, an exaggerated Moro reflex is a clinical feature of neurologic excitability, highlighting the importance of this reflex in assessing infant neurological development 1.

From the Research

Definition and Characteristics of the Moro Reflex

• The Moro reflex (MR) is a primitive reflex that disappears after the first three months of life 2.
• It is characterized by a quick extension-adduction of both arms, followed by orientation of the body, head, and eyes towards a human person, and full extension-abduction of both arms with spreading of the fingers, crying, and a distressed face 3.
• The Moro reflex is due to the activation of an archaic neural circuit present in the newborn, which is later inhibited by the upper brain structures 2.

Neural Mechanism and Location

• The neural centre underlying the Moro reflex is located in the lower part of the brainstem, possibly in the pons 2, 4.
• The reflex can be elicited in anencephalic infants, suggesting that the neural mechanism is located in the brainstem rather than the cortex 2.
• The Moro reflex may involve the activation of the fear and separation-distress systems 3.

Phylogenetic Significance and Ritualization

• The Moro reflex has been proposed to have a phylogenetic significance as a ritualized behavior of nonverbal communication 3.
• The reflex may have evolved as a means of communication, with the gestures associated with the Moro reflex, such as crying and orientation towards a human person, serving as a request to be picked up in the arms 3.
• The Moro reflex may be related to other primitive reflexes, such as the grasp reflex, and may play a role in the hierarchical interrelation among these reflexes 4.

Clinical Significance

• The absence of the Moro reflex during the neonatal period and early infancy is highly diagnostic, indicating a variety of compromised conditions 4.
• The Moro reflex may be related to epileptic spasms and generalized tonic-clonic seizures, which may involve the pathological activation of the same neural archaic circuit involved in the genesis of the Moro reflex 2.