Scientists have identified a surprising mechanism in the brains of mother mice which draws their attention to the calls of baby mice.
The study, by Emory University researchers and published 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," said Robert Liu, assistant professor of biology and senior author of the study.
In 2007, Liu and colleagues were the first to demonstrate that the behavioral context in which communication sounds are heard affects the brain's ability to detect, discriminate and 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 mice pups than auditory neurons in virgin females.
While that experiment was done with anesthetized mice, 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 in the study.
When exposed to the high-frequency whistles of mice pups, which fall into the 60 to 80 kilohertz range, a large area of neurons in the auditory cortex of the mother mice was more strongly inhibited than in the virgin mice. The pattern of excitation of neurons was similar, however, for both the mothers and virgins.
"Something different is happening in the mothers' brains when they are processing the same sound, and this difference is consistent," Liu said.
"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," he added.
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 said.