Infant Development

intro

The newborn infant arrives in the extra-uterine world with numerous movement behaviours that support their survival, interaction with the environment and ability to learn from experience. Movement behaviours present at birth are organised as sensorimotor synergies which can be adapted to changing circumstances and events in the environment. The newborn has three survival behaviours: rooting, the suck-swallow-breathe synergy, and turning the head to free the airway.

These movement behaviours are organised as perceptual-motor synergies  (also referred to as motor patterns) which can be adapted to changing circumstances and events in the environment. Previously these synergies were described as reflexes, but more recent studies have shown that these synergies involve complex patterns of movements adapted to ongoing changes in the environment.

. Rooting

Rooting refers to the infant's tendency to turn their head towards a touch stimulus, applied to the area around the mouth which facilitates turning towards and latching onto the nipple for feeding.

Traditionally rooting was considered to be a stereotypical response to a specific stimulus in other words, it was thought to be a simple reflex. But research has shown that the rooting response adapts to circumstances, for instance, rooting is not elicited when babies or infants touch themselves. [2]

The motion of the infant's head and mouth occurs simultaneously with whole-body movements suggesting rooting is more than a reflex.

2. Sucking

Sucking

Sucking is another newborn behaviour that involves a complex interaction of muscle contractions that are adaptable to the environment. Babies adjust sucking pressure based on the flow of milk by sensing the upcoming flow. “Craig and Lee (1999) found that neonates adjusted their sucking action in a precise and prospective way indicating that they anticipated the upcoming flow of milk.”

Sucking has two phases

creating a temporary vacuum in the mouth region

releasing the milk from the nipple[1

Sucking adaptation can also be seen when newborns suck for comfort instead of food.

3. Head turning to keep airway clear

The ability to lift and turn head to keep airway clear is another perceptual-motor synergy present from birth. [2]

When placed face-down on a supporting surface newborn infants will lift and turn their heads to clear the airway. [2]

Lifting and turning the head involves not only the neck muscles but also requires some adjustments in the upper extremities and trunk muscles to provide some stability to support the neck movements.[1]

The multi-segmented structure of the body provides the basis for producing the varied movement patterns seen in human actions. To simplify control of the many degrees of freedom inherent in a multi-segmented body, spontaneous infant movements are constrained and organised into synergies.

• Lower limb synergy pattern includes intralimb coupling of
  • hip flexion, knee flexion and dorsiflexion
  • hip extension and knee extension

• Upper limb synergy pattern includes a combination of
  • shoulder and elbow extension with extension of the fingers and wrist;
  • flexion of the elbow with finger flexion.

These whole body movements, called general movements or GMs,  are complex and involve the entire body, notably arm, leg, neck, and trunk movements in  variable sequences.

Over the first few months as the infant explores different ways of interacting with the environment and as the frontal motor areas become more active, the strong intralimb coupling lessens as movement are adapted to allow for effective interaction with the environment.

Head Posture

• Head turned to one side In supine the newborn's head is mostly rotated to one side, often with a preference for a particular side, usually to the right. The reason for this tendency is unclear.
• A prominent feature of head rotation in the first two months is the tendency for rotation to be coupled with neck extension and lateral flexion to the opposite side, which is a reflection of the balance in activity between the sternocleidomastoid (SCM) muscles and deep neck flexor muscle activity.
• Over the first few weeks the infant learns to turn the head to the midline, and can sustain the position briefly, especially when supported by visual attention to an interesting person, object or event.
• Typically the head is held in the mid-position for brief periods of time when the infant is actively moving the limbs or is distressed.
• Over the next few weeks the infant will develop the the bilateral antigravity neck muscle strength and control needed to counteract the force of gravity (which creates a turning moment acting on the Center of Gravity (COG) of the head) and maintain the head in the midline for longer periods of time.

Lower Limb Range of Motion, Posture and Kicking

• In infants born at term the range of movement (ROM) of the hips and knees is limited by muscle tightness and increased muscle tone (stiffness) in the lower limbs flexor muscles that result from the flexed posture in the restricted space in the uterus in the last weeks of intrauterine life. This is referred to as neonatal hip flexion contracture.
• During periods of relative quietening of movement
  • the hips are flexed, abducted and laterally rotated and the infant lies with the feet lifted up off the supporting surface (SS)
  • the knees cannot be fully extended and when passively extended they recoil back to a more flexed position.
• Newborn kicking actions
  • characterised by a decrease in the range of hip flexion, along with some extension of the knee
  • the ankle remains in dorsiflexion with the toes in flexion. This relative extension of the hip and knee is followed by a return to the more flexed resting position.

General and fidgety movements

General movements continue to be characterised by writhing movements that involve the head, trunk and extremities in the 1-2 month period. Writhing general movements in the healthy full term infant are described as complex and involve the entire body, notably arm, leg, neck, and trunk movements in variable sequence. They wax and they wane varying in intensity and speed, range of motion, and have a gradual onset and a gradual end. However, towards the end of this period fidgety movements (FMs) are increasingly present.

Writhing general movements in a healthy full term infant are described as complex and involve the entire body, notably arm, leg, neck, and trunk movements in variable sequences. They wax and wane, varying in intensity, speed, and range of motion, and have a gradual onset and end. Rotations around the limb axes and slight changes in the direction of movement create the impression of fluency and elegance.

FMs are small movements of moderate speed with variable acceleration of the neck, trunk, and limbs in all directions. They may appear as early as six weeks after term, but usually occur from around 9 weeks until 16–20 weeks, occasionally even a few weeks longer. They fade out when antigravity and intentional movements start to dominate.

The presence and character of fidgety movements are good indicators of the integrity of the infant's nervous system.