Child abuse: nature or nurture?

Pictured below Vervet monkeys
Monkeys that are abused as infants develop a specific brain change that makes them more likely to mistreat their own offspring, a new study shows.

The findings may help explain why child abuse in humans often perpetuates from one generation to the next, the researchers say.

Dario Maestripieri at the University of Chicago in Illinois, US, and colleagues found that baby rhesus monkeys that endured high rates of maternal rejection and mild abuse in their first month of life produced less of the brain chemical serotonin. Low levels of serotonin are associated with anxiety and depression and impulsive aggression in both humans and monkeys.

The team followed a group of newborn rhesus monkeys with mothers that abused and rejected them. They also studied eight newborn monkeys taken from their birth mothers and placed with abusive ones instead.

Passed down

Analysis of the monkeys’ brain fluid revealed that those reared by abusive mothers or abusive foster mothers had 10% to 20% less serotonin than monkeys who had grown up without maternal abuse. This supports the idea that the drop in serotonin results from mistreatment, rather than a genetic predisposition, says Maestripieri.

Researchers followed the female monkeys into adulthood and found that about half of them abused their own offspring. Those that did abuse their offspring were the ones with the lowest serotonin levels.

The new findings could explain why people who are abused as children may be more likely to be abusive themselves as adults, Maestripieri suggests.

Skills lessons

The study findings suggest that it may be helpful to give abused children antidepressant drugs that raise their serotonin levels, but the prescribing of such drugs to children has become controversial, since some research suggests they may increase suicidal thoughts in youngsters. And experts stress that a drug will not erase the various, long-lasting effects of abuse.

“Chemicals alone aren’t going to fix the problem,” agrees Karen Costa, clinical director of the Child Abuse Prevention Association in Independence, Missouri, US. She explains that therapy plays a key role in treating victims and that parenting skills lessons can help prevent abusive situations occurring in the first place.

Maestripieri agrees that low levels of serotonin alone do not fully explain abuse, which is a complex behaviour. Even if abusive people are shown to have low levels of serotonin, this does not mean they cannot stop their abusive behaviour, he points out. “Biology is never an excuse for anything.”

Journal reference: Behavioral Neuroscience DOI: 10.1037/0735-7044.120.5.1017)

Source: New Scientist