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Mother Mice More Attuned to Mice Pups' Sounds Than Others

Researchers have shown for the first time that the behavioral context in which communication sounds are heard affects the brain’s ability to detect, discriminate, and ultimately respond to them. Specifically, the researchers found that the auditory neurons of female mice that had given birth were better at detecting and discriminating vocalizations from mouse pups than auditory neurons in virgin females.

“Although there have been many studies on communication and neurons in animals, such as in primates, birds, and bats, those studies have focused on how neurons respond to sounds that were already behaviorally relevant to the animals,” says Center for Behavioral Neuroscience member Robert Liu, Ph.D., an Emory University assistant professor of biology and lead author of the study.

The study supported by the Center for Behavioral Neuroscience, a Sloan and Swartz Foundation fellowship, and the National Institutes of Health, was published in the June 12, 2007 issue of PLoS Biology.

“What’s different about this study is that we used natural vocalizations – a range of pup calls – to see how well neurons in mother mice and virgin, or pup-naïve mice, detect, discriminate, and act on this behaviorally important sound,” says Dr. Liu. Ultrasonic calls emitted by mouse pups communicate distress and elicit a search and retrieval response from mothers.

“Our current work demonstrates that the neural code for communication sounds in adult mammals can change, either because of experience or because of hormonal mechanisms, as the significance of the signal is acquired. This means that the brain can improve information processing for specific communicative functions,” says Liu.

Liu began the work as a post- doctoral fellow in the lab of senior author Christoph Schreiner, Ph.D., M.D., professor and vice chair of otolaryngology, head and neck surgery and a member of the W.M. Keck Foundation Center for Integrative Neuroscience at the University of California, San Francisco.
In the study, the researchers determined that the neurons in the mothers’ auditory cortex, an area of the brain that processes sounds, showed larger and earlier electrical spiking, or signaling, than in virgin mice, says Dr. Schreiner.

This shows, says Dr. Liu, that “the timing plays an important role in the neural code of sounds. The idea that spike timing is important in brain processes has been around for a long time, but we’re looking at it specifically in the context of natural communication. And we found that the big difference in encoding is the behavioral relevance of these sounds.”

Although the pups’ vocalizations vary quite a bit, Dr. Liu says the mothers can still detect the calls, understand them, and take action.
“What is really intriguing is that behavioral studies have shown that, if you look at vocalizations made by male adult mice, they also make very high-frequency vocalizations as do pups, but the mothers don’t react to them as they do to the pup calls,” says Dr. Liu.

More research is needed to determine whether mothers recognize pup sounds immediately after they become pregnant, meaning a hormonal switch has been thrown, or after they give birth, says Dr. Schreiner.

Dr. Schreiner likens the improved ability of mother mice to distinguish sounds to what adult humans experience when initially learning a foreign language.

“We go to a foreign country, hear what people are saying, but we can’t make subtle discriminations of syllables in order to establish the border between words. With time and experience the brain is adjusting to this, our neurons becoming more discriminative, and we can distinguish words in what initially just appeared to us as an unbroken stream of sound.”

According to the authors, this study helps demonstrate how important sounds are encoded in the normal brain, and also has implications for developing therapeutic strategies in children and adults who suffer from speech-perception deficits.

Story Courtesy: Robin Tricoles, Emory University
Photo Courtesy: Dr. Robert Liu, Emory University



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