"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.
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."
Showing neural plasticity
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.
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 said. "The auditory cortex has plasticity, so that sounds that become behaviorally relevant to us can get optimized."
More research is needed, he added, 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.
The study authors include Edgar Galindo-Leon, a post-doctoral fellow in Liu's lab, and Frank Lin, a graduate student in the lab. Their research was funded by the National Institute for Deafness and Communication Disorders and the NSF Center for Behavioral Neuroscience.
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