A behavior-analytic understanding of crib death

Lewis P. Lipsitt
Brown University

A verifiable theory of crib death must honor the verities of behavior that are implicated in crib death as well as other conditions of human development, including perinatal risks, that are also clearly involved. Most SIDS deaths occur between two and five months of age; this means that there are protective factors, not least of which may be the behavior of the baby, which spare babies before two months of age but then somehow become less effective. I submit that in the first weeks of life the respiratory occlusion reflex, which occurs in response to threats of smothering or other noxious stimulation around the nose and mouth of the baby, is very effective as an initial defense against smothering. While there are individual differences in the strength of this response, most newborns have a sufficiently strong reflex, manifested in head lifting and swaying, to gain a clear path to breathing when blockage occurs.

Infantile reflexes wane with advancing age between birth and two months of age. But during this period, much learning can occur. Specifically, the baby is reinforced on each occasion that the threat of respiratory occlusion occurs and is followed by a successful, breath-restoring, “escape response.” Over the first two months, babies learn to respond anticipatorily to threats and become adept at engaging in avoidance responses that keep them in “safe territory” for clear breathing. This development of learned expertise is seen especially convincingly as the mother feeds her baby, who adjusts his or her head at the breast in a posture that, increasingly adeptly, avoids occlusion of the nostrils while latching on to the nipple. The mother can usually be seen facilitating this accomplishment as she adjusts contact with the baby’s mouth and nose to reduce the likelihood of occlusion. Thus both classical and operant learning on the baby’s part are likely involved in the process, coupled with operant postural adjustments of the mother.

Why does the age of two months mark the beginning of the period of jeopardy for the small number of babies (two in 1,000) that succumb to crib death? The data and writings of Myrtle McGraw provide some cogent and relevant behavior analyses to help answer this question. Most human babies, she said, undergo a successful behavioral transition during the first two months from a “reflexive” stage of neurobehavioral development to arrive at a stage (usually by 5 months of age) marked by “learned” responses that mimic the initial reflexes. Thus the stepping reflex devolves into walking behavior, and the grasp reflex, initially strong and obligatory, becomes slow, deliberate and effective in reaching for and holding objects. According to McGraw, a developmental or maturational transition occurs as the torch is passed from sub-cortical to cortical mediation of behavior. These neurophysiological changes go hand in hand with experiential processes to promote the acquisition of increasingly complex learned behaviors.

Some babies, viable for the first two months of life, may become especially vulnerable to crib death if they fail to acquire sufficiently strong defensive behaviors needed to prevent respiratory occlusion after the waning of the life-preserving reflex. The recent success of the back-to-sleep directive, urging that babies sleep on their backs rather than in the prone position, supports this neurobehavioral hypothesis. The SIDS rate has been reduced by one-half since the widespread implementation of this caution.

Needed especially at this time are studies to illuminate the specific behavioral mechanisms involved in the acquisition of life-preserving behaviors during development. Behavior analyses of these critical processes may lead to specific interventions that could be used to further reduce the incidence of crib death. An interesting possibility is that newborns with a weak respiratory occlusion reflex might be provided with compensatory training designed to enhance the strength of neuromuscular responses associated with lifting the face, moving the head from side to side, and freeing the respiratory passages for breathing.

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