Reflexes in newborns

Type of psychology: Developmental psychology

Human infants are born with a repertoire of skills that help them adapt to their new environment immediately after birth. By exploring the nature and bases of these early abilities, researchers have gained a better understanding of processes that govern development during the earliest periods of the human life cycle.

Introduction

For many years, it was thought that newborns were completely helpless, fragile and hardly ready for survival in the relatively unprotected world into which they were born. Extensive research has now shown that healthy neonates are born with a set of prepared reactions to the environment that aid their survival. These prepared, inborn reactions are referred to as reflexes.

From the moment of birth, breathing must be self-sufficient, requiring that newborns use their lungs for the first time. They must actively approach, consume, and digest food. During the prenatal period, a fetus receives nutrients passively from the mother, and it discharges waste into the mother’s bloodstream. For the first time, newborns must use their lungs, skin, kidneys, and gastrointestinal tract to regulate digestion and waste elimination.

In addition, newborns are much less protected in the extrauterine environment than they were in the uterus from which they emerged. The developing fetus experiences a world of constancy because of the insulating effects of life in amniotic fluid. At birth, however, newborns first experience fluctuations in air temperature, light, sound, and touch. Neonates will therefore need to be prepared to maintain a relatively constant body temperature and a degree of internal homeostasis—the tendency to maintain internal stability by responding in a coordinated fashion to any changes in the external world—immediately after birth. Reflexes assume many of these functions automatically. From the moment of birth, reflexes are elicited by stimuli in the extrauterine environment. Reflex action is controlled largely by subcortical brain centers in the central nervous system.

Role of Central Nervous System

The human central nervous system (CNS) is organized hierarchically. Simple, uncoordinated actions are controlled by lower, or subcortical, brain centers; coordinated, planned actions are controlled by higher, or cortical, brain centers. Reflexes are among the simplest patterns of action exhibited by humans and are controlled by lower brain centers. The lower brain centers are the most highly developed at birth, and they control the majority of human behavior until they are supplanted by higher cortical brain centers. A few months after birth, the cortical brain centers begin to assume control of the previously reflexive behaviors. That is, as humans develop voluntary control over their behavior, reflexes previously elicited automatically by stimulation no longer respond. This is evidenced by the disappearance of many reflexive behaviors between three and nine months after birth.

Early Survival Responses

The most fundamental reflexes exhibited in newborns involve reactions to unpleasant or life-threatening stimuli. These reflexes protect them from further aversive or possibly life-threatening situations. For example, several reflexes allow newborns to maintain a clear airway for normal breathing. This is important because regular breathing rhythms are not firmly established in newborns; normal, healthy newborns occasionally neglect to breathe for brief periods of time. When this occurs, carbon dioxide builds up in their bloodstreams, and the breathing reflex is triggered. This causes the neonates to start breathing again. Should neonates experience a clogged airway because of mucus or some other obstruction, a reflexive sneeze or cough may serve to remove the obstruction. If something covers a newborn’s face, threatening the passage of air, the defensive reflex is activated, whereby the newborn swats at the object.

Similarly, neonates respond reflexively to the presence of food. At birth, lightly stroking the cheek of an infant will produce a rooting reflex. The rooting reflex is characterized as a head turn accompanied by mouth opening. This turn positions the baby for nutrient seeking via sucking. The sucking and swallowing reflexes enable neonates to consume nutrients, a process that is aided significantly by the activation of other parts of the human digestive tract.

Neonates respond reflexively to changes in temperature and touch. For example, heat causes neonates’ blood vessels to expand so that more heat can be dispersed through the skin. Conversely, cold causes neonates’ blood vessels to contract so that heat can be conserved inside their bodies. Neonates respond to painful physical stimulation such as a pinprick on the foot by reflexively withdrawing the limb. Similarly, neonates respond to loud noises or bright lights by turning away from the source of the aversive stimulus.

Perhaps one of the most general reflexes is the crying reflex. Crying is an important reflex that alerts caregivers that all is not well. Crying is especially important for maintaining homeostasis. Infants cry when they are overstimulated, understimulated, hungry, too cold or hot, in pain, or otherwise uncomfortable. Crying serves to communicate to caregivers as well as to release energy, ward off danger, and possibly clear an air passage.

Primitive Reflexes

Newborns also exhibit a variety of reflexive actions that have no clear survival value. These nonadaptive reflexes are referred to as primitive reflexes. Primitive reflexes disappear early in the first year of life. Several of these primitive reflexes are interesting precursors of abilities that will be exhibited later in life. For example, neonates exhibit an early stepping reflex that closely resembles mature walking. This quickly disappears at about eight weeks of life and reemerges at about twelve to fifteen months as infants take their first true steps. Similarly, newborns will reflexively swim if placed in a prone position on a water surface. Newborns also grasp when the palm is touched. Early versions of both swimming and grasping will disappear in the first three months and, in the case of grasping, will give way first to slapping movements and then to progressive dexterity and the gripping with the palm and fingers at about six months.

Evolutionary accounts of the existence of primitive reflexes in humans suggest that they are remnants of survival reflexes that exist in humans’ evolutionary ancestors. For example, the Moro reflex is a startle reflex observed when an infant is held in a supine position on his or her back and is then suddenly lowered several centimeters. The infant opens his or her arms and then pulls them toward the center of the chest as if grabbing onto something. The Moro reflex serves as a very adaptive clinging response among primates (for example, chimpanzees), which require their infants to hold on to their mother as they travel. For modern humans, however, it is a primitive reflex with no apparent survival value, though its presence in newborns and disappearance within the first six months of life is indicative of normal neurological development.

Practical Applications

Reflex integrity is an important component of several newborn screening instruments. The Brazelton Neonatal Behavior Assessment Scale explores a newborn’s responsiveness to several environmental stimuli as a function of neurological functioning. The Brazelton scale assesses the strength of twenty reflexes as well as a newborn’s ability to respond to twenty-six situations such as orienting to and from a tester’s voice. If an infant is extremely unresponsive, a low Brazelton score may indicate the existence of brain damage or other neurological dysfunction.

Lewis Lipsitt, a researcher studying newborn reflexes, found an important relationship between the integrity of a child’s nervous system and the development of reflexes. Lipsitt conducted research on sudden infant death syndrome (SIDS), a complication in which apparently healthy infants suddenly stop breathing and die in their sleep. The cause of this disorder is unknown. Lipsitt noted that up to 95 percent of SIDS deaths occur when the infants are between two and five months of age, just the time when the neonatal reflexes are moving from subcortical to cortical control. Lipsitt therefore proposed that some infants have a specific disability that keeps them from assuming voluntary control of previously involuntary survival reflexes. As a result, they fail to defend against blockages to their airways in some situations, especially when sleeping. Lipsitt’s work has led to worldwide recognition that the safest sleeping posture for babies in the first six months of life is on the back, because it reduces the risk of airway blockage.

Development in Infancy

The focus on reflexes in newborns has grown because of interest in understanding the rapid development of humans during infancy. Infancy is now understood as the period of most rapid development in a human’s entire life span. During the first two years of life, an infant’s brain will reach 75 percent of its eventual weight. Physical growth will accompany brain growth to enable an infant to display an array of complex motor and cognitive skills that emerge in rapid succession. Developmental psychologists have made considerable progress in understanding this period of development. This progress has been aided by advances in technology and research methods, primarily in the area of brain physiology and function.

Researchers now understand, in contrast to earlier thinking, that humans are born with a variety of skills that aid their survival during this particularly vulnerable developmental period. Previously, researchers, physicians, and parents had assumed that infants were fragile and helpless. Infants are indeed more prepared for life than was previously thought. All major sense organs are functioning at birth, and newborns are capable of learning and experiencing their world actively very shortly after birth.

Nineteenth century psychologist William James described infants as born into a blooming, buzzing confusion. This is clearly far from the truth. Reflexes play an important role in the realization of many early developing abilities. Researchers have used them as a window on the developing nervous system and have understood significant variation in neurological development from the pattern of reflexes. Infants interact with the world reflexively until they have matured enough to engage in more active exploration of their world.

Bibliography

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