Mothers more sensitive to crying babies thanks to hormone, study says

As any bleary-eyed new mother will confirm, the sound of a baby’s cry is almost impossible to ignore, no matter how tired you are feeling. Now scientists have uncovered clues that could help explain why parents are so sensitive to the sound of crying.

A study found that the so-called “cuddle hormone”, oxytocin, which surges following childbirth, changes the way auditory signals are processed in the brains of mice. In effect, the hormone was amplifying the cries of baby mice in the brains of mothers.

“We found that oxytocin turns up the volume of social information processed in the brain,” said Robert Froemke, who led the study at New York University.

When virgin mice were artificially given oxytocin, they too began to hear the crying sounds differently and even began to respond to the cries in the way a mother mouse would, fetching the pups, picking them up by the scruffs of their necks and returning them to the nest.

“It seemed to transform the virgin brain into the more experienced mother,” said Froemke.

Previously it was known that oxytocin is produced during breast feeding and, in general, helps promote bonding between mother and baby, but precisely how it works on the brain has been unknown.

The latest study, in Nature, shows that the hormone changes the way basic sensory signals are processed in the mouse brain.

Further experiments showed that oxytocin was binding to unique receptor cells in the left side of the brain’s cortex, which processes social and auditory information.

The oxytocin did not have the effect in all of the mice, but the researchers were not able to say whether this was due to some animals being “less maternal” than others.

“Maybe these animals just don’t hear very well and so don’t respond,” said Froemke.

Robert Liu, a neuroscientist at Emory University in Atlanta, Georgia, who was not involved in the research, said that it is plausible that the hormone has a comparable effect in humans. “My wife can hear our young child crying in the middle of the night and I don’t even wake,” he said. “I think something similar is happening in the auditory cortex in humans, but you’d need to look for oxytocin receptors in the brain to know whether it is oxytocin causing the effect.”

The findings could lead to a better understanding of how oxytocin and other hormones could be used to treat behavioural problems resulting from disease or trauma to the brain, the researchers said. However, it is unlikely to work as a love-promoting perfume, as some have previously suggested might be possible.

“You have to inhale quite a lot of it to have statistically significant effects on social behaviour,” said Froemke. “I wouldn’t worry too much about oxytocin-based perfumes.”