As toddlers age into the preschool years, their dependency on their parents usually begins to ebb. However, a new study led by Penn State researchers has revealed that physically or psychologically aggressive parenting, such as spanking or shouting, can disrupt this pattern to the detriment of both child and mother, with the child requiring more external regulation, rather than less, as they age.

The research, led by doctoral student Jianing Sun and Professor of Psychology Erika Lunkenheimer and published in Child Development, validates part of a long-standing theory that parents act as the primary physiological regulators for their young children, according to Lunkenheimer. The theory suggests that a parent’s calmer and more regulated state allows the child to better regulate their body’s response in moments of stress — and that this “co-regulation” process becomes more balanced as children age. It is thought that physiological regulation is a two-way street, with parents and children influencing one another’s nervous systems, but the researchers hypothesized and found that the impact from parents to children is more predominant in the preschool years.

“Young children are dependent on their parents’ responses not just to get their needs met, but also to learn appropriate rhythms for regulating their physical and emotional states,” said Lunkenheimer, who is also a co-funded faculty member of the Social Science Research Institute and associate director of the Child Maltreatment Solutions Network. “According to theory, parents’ sensitive and consistent responses foster safety and security, so the child’s nervous system can settle. Beyond parenting behavior, our work suggests that a parent’s calmer, better-regulated physical state while parenting also plays a key role, laying the foundation for how children regulate stress in their body over time.”

Lunkenheimer explained that as preschoolers age, they begin to self-regulate with less dependency on their parents’ input, but there has been very little if any testing of this theory on the biological level. And there’s been even less focus in the field on measuring what happens if the parent’s and child’s co-regulation of stress is disrupted by harsh parenting. According to Lunkenheimer, mothers are at risk of parenting more harshly if they themselves were harshly parented or maltreated as children, and that risk increases when they feel overwhelmed and have more stressors, such as parenting challenges, family conflict, financial or employment difficulties, or greater mental health symptoms.

“We found that lower-risk, less harsh mothers regulated their young children’s physiology during challenging interactions and that maternal influence weakened as the child developed with age,” said first author Sun, a doctoral student in developmental psychology at Penn State. “However, opposite patterns were found for harsher mothers, who showed increasing external regulation of children’s stress physiology and whose children showed more physiological regulatory difficulties as they aged, reflecting their greater risk for developing regulatory problems.”

The researchers observed 129 at-risk mother-child pairs twice, once when the child was three years old and again one year later. Prior to the observations, mothers answered questionnaires about their parenting style, reporting on harsh parenting behaviors, such as if and how often they yell or resort to physical discipline. During the observations, children were given a challenging puzzle task, and mothers were told they could offer verbal guidance but should not complete the puzzle for them.

The pairs were also outfitted with heart and breathing monitors to track their respiratory sinus arrhythmia (RSA), a physiological measurement of how the heartbeat varies with breathing. Changes to RSA over time can act as a measurement of regulation — for example, a person may regulate their system by taking deeper breaths or pausing to calm a rapid heartbeat. RSA dysregulation can continue, however, if a person remains or becomes more stressed.

“When we’re in a challenging situation, the parasympathetic branch of the autonomic nervous system — which controls heart rate and breathing — shifts as our fight or flight response increases to meet that challenge,” Lunkenheimer said, explaining that RSA is an indicator of that change. “RSA has emerged as a sensitive, cost-effective, non-intrusive biological measure. It’s relatively easy to capture in the lab while parents and children are interacting during shared tasks, and it responds quickly. We can see RSA changes based on how mothers and their children interact within five to 30 seconds.”

For this study, the researchers measured RSA in 30-second intervals and found that the mother’s RSA in one interval could predict the child’s in the next, offering evidence that mothers can regulate their child’s physiological state, Sun explained.

“We found that the mother’s RSA in one interval could predict the child’s in the next, offering evidence that mothers can regulate their child’s physiological state,” Sun said. “We also found that in less-harsh mothers, this influence lessened as the child aged from three to four, indicating the child depended less on their mother for this biological regulation,” Sun said. “However, the influence increased in harsher mothers and their children.”

This increase suggests that children who are harshly parented do not regulate stress as well as their peers, which leads to them needing even more external regulation help as they age, Lunkenheimer explained. She said these findings may shed new light on why children who are harshly parented or maltreated show more rigid, less functional stress response systems, possibly as a result of a high-stress environment.

“We found harshly parented children also showed greater RSA inertia: Once challenged, it took longer for their elevated stress level to come back down to baseline,” Lunkenheimer said. “These children may not be receiving the inputs needed to develop their regulatory systems properly — their regulatory system can become more rigid or less responsive.”

Lunkenheimer noted that the team learned much from this study, in significant part due to Sun’s sophisticated statistical work, and that there are several pathways to continue exploring the parent-child co-regulation process, including possible targets for intervention to help at-risk mothers and children better regulate.

“This study did not assess parenting behaviors or interventions, but it provides additional support of what I have found over my career in multiple studies: Children have the best outcomes if parents are sensitive and attuned to their child while also remaining flexible and able to regulate themselves,” Lunkenheimer said. “And that can be really hard — you might be attuned to your child, but then sometimes they throw a huge tantrum when you’re already feeling overwhelmed. Parenting is not always easy, but our work suggests that if you take a moment to regulate yourself — maybe even just pausing and taking a few deep breaths before responding to your child — there’s an important benefit in your child learning how to regulate themselves.”

Co-authors include Longfeng Li, assistant professor of human development and family science at Florida State University who completed a postdoctoral fellowship at Penn State under Lunkenheimer’s mentorship; and Sy-Miin Chow, professor of human development and family studies, Social Science Research Institute co-funded faculty member and director of the Quantitative Development Systems Methodology Core at Penn State.

The Eunice Kennedy Shriver National Institute of Child Health and Human Development and the National Center for Advancing Translational Sciences funded this work.

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