Brain circuits may control parental behavior

Scientists from Harvard University have discovered brain circuits in mice that control parental behavior.istockphoto

Parenthood has been the subject of endless advice books, daytime talk shows, and movies. But what really turns new parents into nurturing moms and dads? New research suggests it might start with a simple switch in the brain.

Scientists from Harvard University have discovered brain circuits in mice that control parental behavior, and they were able to induce abrupt transformations — making abusive male mice act like doting fathers, for example — through simple manipulations that one outside researcher called stunning.

Turning mice into good parents did not take lessons, social workers, or an intervention: It was as simple as shining a light to trigger specific brain cells.

“Behaviors such as caring for the young are absolutely essential for the survival of the species, so the fact that in the brain there are centers that make sure animals go through those behaviors at the right time, upon the right stimulation is no surprise,” said Catherine Dulac, a professor of molecular and cell biology at Harvard University, who led the work published Wednesday in the journal Nature. “The fact that we are mammals means we certainly have those neurons as well.”

Dulac is quick to point out the obvious differences between how mice raise their young and how people do; human parenting is a complex enterprise, with layers of social information and complex cognitive processes integrated on top of any primal brain circuits. But she said that the new research gives insight into powerful neural circuits that govern parental behavior at a basic level.

There has been keen interest in neuroscience in finding slight structural differences between male and female brains that might explain gender differences in behavior. But Dulac found that a key brain circuit that controls parental behavior looks identical in male and female mice — a finding that she suggests has implications for fathers’ potential to be as nurturing as mothers.

“When I present this data, I very often have some of my male colleagues come to me and they are just thrilled,” Dulac said. “It’s the same between males and females — they can do it, absolutely.”

The new research also might provide a toehold into understanding the other brain processes involved in parenting, which can go awry in conditions such as post-partum depression.

“These particular findings right here may not be very easily extrapolated to humans at this point,” said Larry Young, a psychiatry professor at Emory University School of Medicine and the researcher who described the results as stunning. But he said the advanced techniques used by the Harvard team provide a new entry point to understand how the brain controls parenting behaviors. Many key questions remain, he said, including how the parenting brain circuits get triggered in the first place.

The Harvard team started out with a simple observation. In animals ranging from rats to lions to monkeys, parental behavior differs drastically between males and females. In some species, for example, a male will attack pups. But the researchers were intrigued by reports in the scientific literature that male mice that normally attack pups cease that aggressive behavior for a short window three weeks after mating — just when their own pups would be born.

They began searching for the brain circuits that might play a role in this phenomenon and focused first on a brain region involved in sensing pheromones, scents that influence the behavior of other animals. The region had been shown to be important in mating and courtship behaviors.

The researchers destroyed those brain cells and found that virgin male mice that typically attacked young pups suddenly began to act like nurturing dads — retrieving the pups, building nests, and grooming them.

Then, the scientists looked for other brain circuits that might be involved, and settled on a promising subset of nerve cells in the middle of the brain.

When they destroyed these neurons, which produce a protein called galanin, in virgin female mice, they found that the mice that normally acted motherly began to act more aggressively, like young males. They attacked the pups, stopped huddling with them, and markedly decreased grooming and building nests.

When scientists destroyed the neurons in mothers nursing pups, the mice no longer retrieved their pups. Males that lost those brain cells never started acting like dads at a time they normally would have been grooming pups and building nests.

Then, using a cutting-edge technique called optogenetics, which uses genetic manipulation to make specific brain cells light-sensitive, the team was able to test what happened when they turned those crucial brain cells on. By essentially flipping a light switch that activated the brain cells, they were able to turn cads into dads, causing virgin males to start grooming pups. These males also became less likely to pick fights with other mice and increased the amount of time they spent moving around.