hormones

Mice mom better at answering baby’s call

EMORY (US)—A surprising mechanism in the brains of mother mice focuses their awareness on the calls of baby mice, according to researchers at Emory University.

A study led by Robert Liu, assistant professor of biology, shows that female mice that have given birth were better than virgin mice at detecting and understanding vocalizations from mice pups. The study, published June 11 in Neuron, found that the high-frequency sounds of mice pups stand out in a mother’s auditory cortex by inhibiting the activity of neurons more attuned to lower frequency sounds.

“Previous research has focused on how the excitation of neurons can detect or interpret sounds, but this study shows the key role that inhibition may play in real situations,” says Liu.

The current study by Liu’s lab is the first to record the activity of neurons in the auditory cortex of awake mice. Both female mice that had given birth and virgin female mice with no experience caring for mice pups were used.

When exposed to the high-frequency whistles of mice pups a large area of neurons in the auditory cortex of the mother mice was more strongly inhibited than in the virgin mice.

“Something different is happening in the mothers’ brains when they are processing the same sound, and this difference is consistent,” Liu explains. “The inhibition of neurons appears to be enhancing the contrast in the sound of mice pups, so they stand out more in the acoustic environment.”

Liu says more research is needed to determine whether the changes in the brains of mother mice is due to hormonal shifts, the behavioral experience of caring for pups, or both.

Liu’s research focuses on how the brain evolves to process sounds in the natural environment. “By understanding normal functioning of the auditory processes in the brain, then we can begin to understand what is breaking down in disease situations, such as following a stroke or brain lesion,” he notes.

Until recently, it had been widely assumed that the auditory cortex acted simply as a static filter, and that areas downstream in the brain did the complex task of learning to parse meaning from sounds.

“What our experiments help demonstrate is that even at this relatively early stage of cortical sound processing, responses are dynamic,” Liu says. “The auditory cortex has plasticity, so that sounds that become behaviorally relevant to us can get optimized.”

The study was funded by the National Institute for Deafness and Communication Disorders and the NSF Center for Behavioral Neuroscience.

Emory University news: www.emory.edu/esciencecommons

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