Developmental Reflexes: A Disappearing Act

Developmental Reflexes

Developmental reflexes, also known as primitive reflexes or neonatal reflexes, are generally present at birth (exceptions include the Landau and parachute reflexes) and offer a useful way to assess neurological function in infants.

Developmental reflexes develop during gestation, persisting for several months after birth to prepare the infant for the acquisition of specific skills. In other words, as the CNS matures, the reflexes are inhibited to allow the infant to make purposeful movements. For example, while the asymmetric tonic neck reflex is present, an infant is unable to roll over, bring the hands to midline, or reach for objects. This reflex disappears between 3 and 4 months of age, around the same time that these skills begin to emerge. Similarly, the Moro reflex interferes with head control and sitting equilibrium. As this reflex lessens and disappears by 6 months of age, the infant gains progressive stability in a seated position.

Postural reactions also begin to develop after birth. For example, protective extension allows the infant to catch themselves when falling forward, sideways, or backwards. These reactions develop between 6 and 9 months of age, the same time that infants typically learn to move into a seated position, crawling, etc. Soon afterward, infants develop equilibrium responses that permit pulling to stand and walking. 

Source: Gerber et al. Developmental milestones: motor development. Pediatr Rev. 2010 Jul;31(7):267-76

Interestingly, following their disappearance, developmental reflexes may reappear later on in life in the presence of degenerative disorders, particularly those affecting the frontal lobes.

Developmental reflexes are considered abnormal if they are

  • absent during the neonatal period
  • asymmetric (suggesting hemiplegia or monoplegia)
  • persistent beyond the age by which they should have normally disappeared

Developmental Reflexes Present at Birth

Rooting reflex

  • Reflex: When the infant’s cheek or mouth is touched, the rooting reflex causes the infant to turn their head toward the stimulus 
  • Disappears at 3-4 months of age, but may persist longer in sleep
  • Example

Sucking reflex

  • Reflex: Placing something in the infant’s mouth (e.g., nipple of breast or bottle) causes them to suck and draw liquid into the mouth
  • Disappears at 3-4 months of age, but may persist longer in sleep

Stepping reflex

  • Reflex: When an infant is held in an upright vertical position while touching the feet to a flat surface, the feet move in an alternating stepping motion
  • Disappears at 3-4 months of age
  • Example

Moro reflex

  • Reflex: A sudden downward position change of an infant’s head leads to symmetric extension and abduction of the fingers and arms, followed by flexion of the arms 
    • An asymmetric response can signify a fractured clavicle, brachial plexus injury, or hemiparesis
    • Absence of the Moro reflex in a term newborn is ominous, suggesting significant dysfunction of the CNS
  • Disappears at 3-6 months of age
  • Example

Palmar / plantar grasp reflex

  • Reflex: Placing a small object or finger in an infant’s palm (or just beneath toes) causes fingers (or toes) to curl around object or finger 
  • Palmar grasp disappears at 3-4 months of age (allows for maturing grasp); plantar grasp disappears at 9-12 months of age (allows for walking)
  • Example

Withdrawal reflex

  • Reflex: An infant reflexively moves their hand or foot away from painful stimuli
  • Present for life

Asymmetric tonic neck reflex

  • Reflex: When supine, turning an infant’s head to the side leads to extension of the arm and leg on the side the head is turned while flexing the opposite arm and leg 
    • An obligatory tonic neck response, in which the infant becomes stuck in the fencing posture, is always abnormal and implies a CNS disorder
  • Disappears at 3-4 months of age (allows for rolling over)
  • Example

Crossed adductor reflex

  • Reflex: Tapping an infant’s patellar tendon on one leg causes contraction in the opposite leg
  • Disappears at 6-7 months of age
  • Example

Babinski reflex

  • Reflex: Stroking the bottom of an infant’s foot causes toes to dorsiflex and fan out while the foot twists in 
  • Disappears at 9-10 months of age
  • Example

Developmental Reflexes that Present After Birth

Landau reflex

  • Reflex: When an infant is suspended horizontally and prone, flexing an infant’s head against the trunk, leads to the legs flexing against the trunk 
  • Appears at 3-4 months of age; disappears at 1-2 years of age
  • Example

Parachute reflex

  • Reflex: When an infant is suspended in the prone position or head downwards, suddenly moving the infant downward causes the hands and fingers to extend forward and spread 
  • Appears at 7-9 months of age (making this reflex a prerequisite to walking); present for life
  • Example