Primitive Reflexes

The earliest motor neuromaturational markers are primitive reflexes that development during uterine life and generally disappear between the third and sixth months after birth. Newborn movements are largely uncontrolled, with the exception of eye gaze, head turning, and sucking. Development of the infant’s central nervous system involves strengthening of the higher cortical center that gradually takes over function of the primitive reflexes. Postural reflexes replace primitive reflexes between three and six months of age as a result of this development (Schott and Rossor, 2003). These reactions allow children to maintain a stable posture even if they are rapidly moved or jolted (Box 2-1).

The asymmetric tonic neck reflex (ATNR) or “fencing posture” is an example of a primitive reflex that is not immediately present at birth because of the high flexor tone of the newborn infant. When the neonate’s head is turned to one side, there is increased extensor tone of the upper extremity on the same side and increased flexor tone on the occipital side. The ATNR is a precursor to hand-eye coordination, preparing the infant for gazing along the upper arm and voluntary reaching. The disappearances of this reflex at 4 to 6 months allows the infant mobility to roll over and begin to examine and manipulate objects in the midline with both hands.

The palmar grasp reflex is present at birth and persists until 4 to 6 months of age. When an object is placed in the infant’s hand, the fingers close and tightly grasp the object. The grip is strong but unpredictable. The waning of the early grasp reflex allows infants to hold objects in both hands and ultimately to voluntarily let them go.

The Moro reflex is probably the most well-known primitive reflex and is present at birth. It is likely to occur as a startle to a loud noise or sudden changes in head position. The legs and head extend while the arms jerk up and out, followed by adduction of the arms and tightly clenched fists. Bilateral absence of the reflex may mean damage to the infant’s central nervous system. Unilateral absence could indicate birth trauma such as a fractured clavicle or brachial plexus injury.

Postural reflexes support control of balance, posture, and movement in a gravity-based environment. The protective equilibrium response can be elicited in a sitting infant by abruptly pushing the infant laterally. The infant will extend the arm on the contralateral side and flex the trunk toward the side of the force to regain the center of gravity (Fig. 2-1). The parachute response develops around 9 months and is a response to a free-fall motion, where the infant extends the extremities in an outward motion to distribute weight over a broader area. Postural reactions are markedly slow in appearance in the infant who has central nervous system damage. Children who fail to gain postural control continue to display traces of primitive reflexes. They also have difficulty with control of movement affecting coordination, fine and gross motor development, and other associated aspects of learning, including reading and writing. Table 2-2 is a list of the average times of appearance and disappearance of the more common primitive reflexes.

FIGURE 2-1 The protective equilibrium response is demonstrated in an infant being pushed laterally. Note the extended contralateral arm.

TABLE 2-2 Primitive Reflexes

Gross Motor Skills

One principle in neuromaturational development during infancy is that it proceeds from cephalad to caudad and proximal to distal. Thus, arm movement comes before leg movement (Feldman, 2007). The upper extremity attains increasing accuracy in reaching, grasping, transferring, and manipulating objects. Gross motor development in the prone position begins with the infant tightly flexing the upper and lower extremities and evolves to hip extension while lifting the head and shoulders from a table surface around 4 to 6 months of age. When pulled to a sitting position, the newborn has significant head lag, whereas the 6-month-old baby, because of development of muscle tone in the neck, raises the head in anticipation of being pulled up.

Rolling movements start from front to back at approximately 4 months of age as the muscles of the lower extremities strengthen. An infant begins to roll from back to front at about 5 months. The abilities to sit unsupported (about 6 months old) and to pivot while sitting (around 9 to 10 month of age) provide increasing opportunities to manipulate several objects at a time (Needleman, 1996). Once thoracolumbar control is achieved and the sitting position mastered, the child focuses motor development on ambulation and more complex skills. Locomotion begins with commando-style crawling, advances to creeping on hands and knees, and eventually reaches pulling to stand around 9 months of age, with further advancement to cruising around furniture or toys. Standing alone and walking independently occur around the first birthday. Advanced motor achievements correlate with increasing myelinization and cerebellum growth. Walking several steps alone has one of the widest ranges for mastery of all of the gross motor milestones and occurs between 9 and 17 months of age. Milestones of gross motor development are presented in Table 2-3 and Figure 2-2. The accomplishment of locomotion not only expands the infant’s exploratory range and offers new opportunities for cognitive and motor growth, but it also increases the potential for physical dangers (Vaughan, 1992).

TABLE 2-3 Cognitive and Language Communication Skills Development