In what is apparently the first investigation to look at the neuronal effects of spanking alone rather than its effects when accompanied by other kinds of physical punishment, researchers found that children who had been spanked showed greater brain activity after being exposed to threatening stimuli than those who had never been spanked, closely mirroring a pattern seen in children who have experienced more severe forms of maltreatment.

The study, conducted by University of North Carolina at Chapel Hill, Harvard University and University of Washington researchers and published in Child Development on April 9, adds to a growing body of evidence that corporal punishment — a practice that is legal in over 130 nations, including the United States — could elevate the risk of mental health and developmental issues in some individuals.

Jorge Cuartas, a doctoral student in education and human development at Harvard and the study's lead author, explained that our brains are fine-tuned to detect threats in the environment and respond quickly in order to avoid potential danger. "If we are exposed to those threatening experiences on a regular basis, that can produce long-lasting changes in our brain for us to be more prepared to respond to future threats," Cuartas told The Academic Times. "Spanking, in particular, can have such consequences, according to this study."

Prior investigations have shown that corporal punishment is associated with externalizing or internalizing behaviors, as well as with aggression, anxiety and depression, Cuartas said. But scientists hadn't yet determined spanking's effects in isolation.

To focus on the effects of spanking by itself, the researchers utilized a longitudinal dataset made up of children tracked and assessed throughout their childhood, starting between the ages of 3 and 5. At the time of the study, the children were between the ages of 10 and 12. Children who had faced more severe forms of punishment or abuse were excluded from the study so that the scientists could pinpoint how spanking, in particular, impacted childhood development.

In the study, 40 children who had been spanked and 107 children who hadn't been spanked participated in functional magnetic resonance imaging scans while being exposed to a series of rapidly changing faces, presented in nine blocks. Each block consisted of 36 actors with the same facial expression, and the blocks alternated between neutral faces, fearful faces and indistinguishable, scrambled faces, meant to resemble random static. 

Both children who had been spanked and children who had not been spanked showed more activity in several regions of the brain when viewing fearful faces than when viewing neutral ones. But compared with the children who had never been spanked, those who had been spanked displayed more pronounced levels of activity, especially in the medial and lateral prefrontal cortex — areas of the brain responsible for cognitive function, including attention control, decision-making and emotion maintenance. Similar neural responses have been observed in children who have experienced more severe forms of violence. 

Surprisingly, the researchers did not detect significant differences in amygdala activity between populations that were spanked and those that were not. The amygdala, part of the brain's salience network, helps the brain detect relevant stimuli and identify threats in one's surroundings. The network has been shown to be more active in children who have previously been exposed to violence, as established in at least seven prior studies, according to the paper.

The findings lend credence to the dimensional model of adversity, a framework that suggests adverse childhood experiences can "have similar influences on emotional and neural development that will scale in relation to the severity of the threat experienced," the researchers wrote. The model also helps explain the correlation between the presence of violence in childhood and subsequent negative mental and emotional outcomes in adulthood.

Cuartas explained that the underlying motivations for employing corporal punishment — inflicting intimidation and physical pain on children — are the same ones that lead to developmental problems among children. "Corporal punishment, by definition, is the use of physical force to cause children to feel pain or fear, in order to change their behavior," he said. "It's causing children to feel threatened, which is exactly what we know can lead to these neurodevelopmental outcomes for children."

Although the rate of corporal punishment has declined in recent years, around 35% of parents report spanking their kids, according to a JAMA Pediatrics study published in 2020, based on surveys from 2017. Other studies have indicated that spanking is correlated with a higher likelihood of more severe forms of abuse, especially if the spanking involves striking a child with an object.

Cuartas said policy changes to ban corporal punishment in the U.S. and internationally — both in the home and at school — could play a role in avoiding potentially lifelong developmental problems in many children. Parent training programs could also help parents learn healthier, more positive disciplinary strategies.

Although not everyone who is spanked will go on to experience atypical brain development, Cuartas said it would be safer to avoid spanking altogether. "We have to see this research [much] as we think about smoking, for example. We know that not everyone who smokes is going to develop lung cancer or lung disease. But we know that smoking increases dramatically the risk of those types of illnesses," he said. "I think that the accurate thing to say is that corporal punishment can increase risks. And for that reason, we should avoid its use."

The study, "Corporal punishment and elevated neural response to threat in children," published April 9 in Child Development, was authored by Jorge Cuartas, David G. Weissman and Katie A. McLaughlin, Harvard University; Margaret A. Sheridan, University of North Carolina at Chapel Hill; and Liliana Lengua, University of Washington.