Retained Primitive Reflexes

The human infant is born at a premature stage of its development in terms of its motor skills compared to many other animals. A baby cannot even lift their head compared to many animals who can get to their feet within minutes of being born. Yet in the first nine months after birth the child’s motor skills undergo a remarkable development. Within 6 weeks they can raise their head off the ground when lying on their tummy, a few weeks later they can support their weight on their forearms, the child then learns to roll, then they learn to creep on their stomach which is followed by the ability to sit semi-upright. By 6 months of age the child begins to crawl on hands and knees and by 12 months they begin to walk. The preparation for each of these stages is accompanied by particular stereotyped reflex motor movements. These reflexes are automatic involuntary movements, which are under the control of the most primitive part of the brain (brainstem). Ideally each of these reflexes is short lived and has fulfilled its function once the child reaches the developmental milestone when it is replaced by more complex responses (postural reflexes), which are controlled by the more sophisticated regions of the brain (cortex). The reflexes may be retained in some children if they do not fulfill their desired function or may be evidence of immaturity or delayed development of the central nervous system. Factors such as prematurity, birth trauma, stress during pregnancy and genetic factors may affect the attainment of these developmental milestones.

Many children who demonstrate retained reflexes have difficulty suppressing unwanted movements. For example if the child is asked to move their left arm and right leg at the same time often their other body parts will move also (ie. the right arm or left leg), which is called overflow. Consequently the child is prone to fidgeting, is often clumsy, has difficulty with eye-hand co-ordination, handwriting and balance.

Eye tracking skills are particularly affected by retained reflexes. In order to read fluently we need to move our eyes smoothly from one word to the next. These eye movements are known as saccades. Saccades can be voluntary which are under our conscious control or they can be reflexive. Reflexive saccades move our eyes in the direction of any stimulus in our peripheral vision which attracts our attention. The majority of people are able to suppress these reflexive saccades but many children especially those with ADHD and dyslexia cannot, which affects their ability to track across the page causing them to frequently lose their place and forcing them to use their finger as a marker.

Retained reflexes can affect children in more subtle ways. One parent told me that she could never figure out why her child continually kicked those next to him when he was learning to dance, it was because of these reflexes! When a dance move required only the movement of his arms his legs would move involuntarily and vice versa when a move required that he move only his feet his arms would move reflexively.

One of the most notable reflexes which affects vision and learning is the Asymmetric Tonic Neck Reflex (ATNR). This reflex develops 18 weeks after conception and aids the baby’s ability to move down the birth canal at delivery. Effectively when the baby moves their head to one side, the arm and leg on that side extend and the arm and leg on the other side flex. This reflex is responsible for the ‘kick’ an expectant mother feels when the child moves in the womb for the first time. The reflex also aids the baby after they are born, in the first few weeks of life the ATNR can be readily seen when a baby lying on their back turns their head to one side. This head rotation causes an extension of the arm. The new born is not aware that their hands are part of themselves therefore any movement of the hand in their visual field attracts their attention and stimulates fixation. As a result head, hand and eye movements are locked together into a single movement. In effect during these first few weeks the baby is learning eye-hand co-ordination by focusing and aiming their eyes on their hand. If the child has a weak ATNR, if the reflex is haphazard or lacks precision then these skills may develop poorly.

At around 6 months of age the ATNR is gradually inhibited, which means eye and hand movements are gradually free of head movements. Unfortunately for many children the reflex persists meaning that every time the child moves their eyes their head will move and vice versa. Eye movements are more efficient if the head is still and acts as a stationary reference point as this creates greater stability of the image on the retina. Children who move their head when reading are more likely to be slow dysfluent readers.

A retained ATNR greatly affects the development of bilateral integration or the ability to perform cross lateral movements. For example when learning to crawl it is important that each side of the body moves equally and in concert. If one side of the body is rigid and extended whilst the other is flexed and floppy the child will be unable to crawl effectively. Many children who demonstrate a retained ATNR often have a history of not crawling, crawling for short periods or crawling inefficiently such as commando crawling. Swimming is another highly cross-lateral skill, children who demonstrate a retained ATNR often have difficulty in the pool. As a result of the difference in muscle tone between the two sides of the body these children also have difficulty using both hands at the same time which causes them to drop objects and appear generally clumsy. Balance can be adversely affected if the reflex is strongly retained in the legs, as the head looks from left to right one leg becomes rigid the other floppy, which upsets their centre of gravity.

A retained ATNR is a major cause of handwriting difficulties, every time the child turns their head to the right, their right arm and fingers reflexively stretch or extend. To hold a pencil when writing our fingers need to be flexed. The child may compensate for this reflexive stretching of their fingers by holding the pencil with an unusual grip or applying excessive pressure, which causes messy writing and cramping of the hand.

The ATNR affects a child’s ability to cross their midline (centre of the body). If the child is asked to pick up a block on their right side and then place it at the left edge of the table when the child turns their head to the left the right hand will become floppy causing them to drop the block. Consequently many children develop strategies of avoiding crossing their midline. When writing instead of beginning at the left margin the child may start in the middle of the page. They may try to pass a crayon from their right hand to their left hand rather than try to cross the midline, as a result the child may continue to alternate hands when writing rather than developing a dominant hand (side).

This reflex can still impair us later in life, many car accidents have been attributed to this reflex. If we turn our head to look over our shoulder into the blindspot our arm which is holding the steering wheel can move reflexively causing the car to veer off course.

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