Afraid is better (Image: Tsuneo Yamashita/Getty)

Even at the tender age of 3, children who will go on to be convicted of a crime are less likely to learn to link fear with a certain noise than those who don’t. This may mean that an insensitivity to fear could be a driving force behind criminal behaviour.

Adult criminals tend to be fearless, but whether this characteristic emerges before or after they commit a crime wasn’t clear, says Adrian Raine, a psychologist at the University of Pennsylvania in Philadelphia.

To find out, Raine and colleague Yu Gao turned to data from a 1970s study, collected as part of a decades-long project to understand the biological and environmental factors underlying mental illness.


Back then, researchers led by Raine’s former research supervisor had measured the sweat response of about 1800 3-year-olds in Mauritius when they were exposed to two different sounds. One sound was always followed by a noisy blare, the other by nothing. The children learned to anticipate which sound preceded the blare, and sweated in response to it – an indicator of fear.

Decades later, Raine’s own team looked to see if any of the subjects had criminal records and found 137 that did. The team discovered that, as toddlers, these people had sweated significantly less in anticipation of the blare compared with subjects of similar race, gender and background for whom no criminal record was found.

Reducing crime

“I think it’s a very interesting, potentially important finding,” says Joseph Newman, a psychologist at the University of Wisconsin-Madison.

However, he cautions that the existence of early predictors of criminal behaviour does not mean that some children are born criminals. “There are many causes of crime, and there are many things that underlie fear conditioning,” he says.

The differences in fear sensitivity are likely to be innate, at least in part: dysfunction in the amygdala, a brain area important for processing fear, has previously been linked to psychopathic behaviour, and genetic factors must underlie some of these differences.

However, numerous children who showed muted responses to fearful cues never fell foul of the law, Raine says. “Is this a throw-away-the-key approach to criminals? Absolutely not,” he says.

Raine emphasises that environment can make someone less likely to commit a crime. He points to other studies from his team, also based on data from Mauritius, which indicate that manipulating a child’s surroundings with improved nutrition, more exercise and cognitive stimulation, can reduce the chance they will commit a crime later on in life.

Journal reference: American Journal of Psychiatry, DOI: 10.1176/app1.ajp.2009.09040499