Predicting Externalizing Behavior in Infants

Yukta Kulkarni ’22

Figure 1:  Infants can respond to the environments they grow in and react accordingly.

The minds of children are malleable and easily influenced by the circumstances they are placed into. Their experiences in early life can elicit certain actions according to the emotions they may not be able to process and control. This can be defined as externalizing behavior. More often than not, children who face trauma or stress such as abuse or poverty have higher rates of behavioral issues and outbursts throughout their life, some even starting before they reach the age of one. Biologically, modifications in stress-response systems are seen in these children. Dr. Allison Frost and her team focused on two such systems called the hypothalamic-pituitary-adrenal axis (HPA) and the autonomic nervous system (ANS). They wanted to determine if the two markers of the aforementioned systems, salivary cortisol and alpha-amylase, respectively, interact with each other and if these interactions could predict how an infant would react to stress.

The researchers focused on poverty as the stressor, including 179 parents and their infants (6-20-month-olds) living in predominantly low-income households. It was determined who could participate in the study by administering a socioeconomic questionnaire. Those who fit the criteria collected their infant’s saliva samples three times a day – once when they woke up, 30 minutes after waking up, and before they went to sleep – for three days. The saliva data was analyzed and illustrated in regression models. The parents also had to take the Infant Externalizing Questionnaire to determine the level of aggressive behavior the infant was expressing, as well as if the infant was being defiant. The results of the analysis show a significant connection between cortisol and alpha-amylase effects in the morning. When infants in this study showed fewer amounts of externalizing behavior in the morning, their cortisol levels were low, while their alpha-amylase levels were high.

These findings are important because it demonstrates that multiple systems sometimes simultaneously affect the behavior of people. This especially affects infants since they are young and can be easily influenced. This can also change the way parents view their children during a tantrum. If they are educated on how infants process information and react, parents can alter the circumstances the children are placed in. More studies need to take place to concretely conclude that the relationship between salivary cortisol and alpha-amylase can lead to fewer or more outbursts of externalizing behavior. 


[1] A. Frost, et al., Externalizing behavior and stress system functioning in infants exposed to early adversity: A multi-system exploration. Developmental Psychobiology 63, 1255-1265 (2021). doi: 

[2] Image retrieved from: 


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