Primitive reflexes

Primitive reflexes are reflex actions originating in the central nervous system that are exhibited by normal infants but not neurologically in tact adults, in response to particular stimuli. These reflexes disappear or are inhibited by the frontal lobes as a child moves through normal child development.^[1] These primitive reflexes are also called infantile, infant or newborn reflexes.

Older children and adults with atypical neurology (for instance, people with cerebral palsy) may retain these reflexes and primitive reflexes may re-appear in adults due to certain neurological conditions including, but not limited to, dementia, traumatic lesions, and strokes.^[2][3] An individual with cerebral palsy and typical intelligence can learn to suppress these reflexes, but the reflex might resurface under certain conditions such as during an extreme startle reaction. Reflexes may also be limited to those areas affected by the atypical neurology, such as individuals whose cerebral palsy affects only their legs retaining the Babinski reflex but having normal speech. In individuals with hemiplegia, the reflex might be seen in the foot on the affected side only.

Primitive reflexes are also tested with suspected brain injury to test the functioning of the frontal lobe. If they are not being suppressed properly they are called frontal release signs. Atypical primitive reflexes are also being researched as potential early warning signs of autistic spectrum disorders.^[4]

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Moro reflex

Main article: Moro reflex

  This is sometimes referred to as the startle reaction, startle response, startle reflex or embrace reflex. It is more commonly known as the Moro response or Moro reflex after its discoverer, pediatrician Ernst Moro.

The Moro reflex is present at birth, peaks in the first month of life and begins to disappear around 2 months of age. It is likely to occur if the infant's head suddenly shifts position, the temperature changes abruptly, or they are startled by a sudden noise. The legs and head extend while the arms jerk up and out with the palms up and thumbs flexed. Shortly afterward the arms are brought together and the hands clench into fists, and the infant cries loudly.^[5] The reflex normally disappears by three to four months of age,^[6] though it may last up to six months.^[7] Bilateral absence of the reflex may mean damage to the infant's central nervous system while a unilateral absence could mean an injury due to birth trauma such as a fractured clavicle or injury to the brachial plexus. Erb's palsy or some other form of paralysis is also sometimes present in such cases.^[6]

Walking/stepping reflex

  The walking or stepping reflex is present at birth; though infants this young can not support their own weight, when the soles of their feet touch a flat surface they will attempt to 'walk' by placing one foot in front of the other. This reflex disappears as an automatic response and reappears as a voluntary behavior at around a year old.

Rooting reflex

The Rooting reflex is present at birth and assists in breastfeeding, disappearing at around four months of age as it gradually comes under voluntary control. A newborn infant will turn their head toward anything that strokes their cheek or mouth, searching for the object by moving their heads in steadily decreasing arcs until the object is found. After becoming used to responding in this way (if breastfed, approximately three weeks after birth), the infant will move directly to the object without a "search".

Sucking reflex

The sucking reflex is common to all mammals and is present at birth. It is linked with the rooting reflex and breastfeeding, and causes the child to instinctively suck at anything that touches the roof of their mouth. There are two stages to the action:

1. Expression: activated when the nipple is placed between a child's lips and touches their palate. They will instinctively press it between their tongue and palate to draw out the milk.
2. Milking: The tongue moves from areola to nipple, coaxing milk from the mother to be swallowed by the child. Coordination on of these movements with breathing and swallowing is instinctual, but not perfect.

Tonic neck reflex

Main article: Asymmetrical tonic neck reflex

The tonic neck reflex, asymmetric tonic neck reflex or 'fencing posture' is present at birth and disappears at around four months. When the child's head is turned to the side, the arm on that side will straighten and the opposite arm will bend (sometimes the motion will be very subtle or slight). If the infant is unable to move out of this position or the reflex continues to be triggered past six months of age, the child may have a disorder of the upper motor neurons.

Palmar grasp reflex

  The palmar grasp reflex appears at birth and persists until five or six months of age. When an object is placed in the infant's hand and strokes their palm, the fingers will close and they will grasp it. The grip is strong but unpredictable; though it may be able to support the child's weight, they may also release their grip suddenly and without warning. The reverse motion can be induced by stroking the back or side of the hand.

Plantar reflex

Main article: Plantar reflex

The plantar reflex or plantar grasp is present at birth and fades around the infant's first birthday. The plantar reflex causes the infant's toes to curl up tightly when something rubs the ball of their foot.  

Babinski reflex

Often confused with the plantar reflex, the Babinski reflex is also present at birth and fades around the first year. The Babinski reflex appears when the side of the foot is stroked, causing the toes to fan out and the hallux to extend. The reflex is caused by a lack of myelination in the corticospinal tract in young children. The Babinski reflex is a sign of neurological abnormality in adults.

Galant reflex

Main article: Galant reflex

The galant reflex, also known as Galant’s infantile reflex, is present at birth and fades between the ages of four to six months. When the skin along the side of an infant's back is stroked, the infant will swing towards the side that was stroked. If the reflex persists past six months of age, it is a sign of pathology. The reflex is named after the Russian neurologist Johann Susman Galant.^[8]

Other primitive reflexes tested in adults

As mentioned these are generally referred to as frontal release signs although this may be a misnomer. They include the palmomental reflex, snout reflex, glabellar reflex or "tap", in addition to some of those mentioned above .

References