June 10, 2009
New Insight Into Maternal Auditory Cortex Plasticity
A recent study reveals changes specific to the mother mouse brain that may improve the detection of isolation calls from a mouse baby. The research, published by Cell Press in the June 11th issue of the journal Neuron, provides fascinating new insight into how call-evoked neural inhibition plays a key role in the brain's representation of this important communication vocalization.
"One of the fundamental tasks of the auditory system is to process species-specific communication sounds. In mammals, the auditory cortex is thought to be essential for this," says senior study author Dr. Robert C. Liu from the Department of Biology at Emory University. "Although previous work with anesthetized animals has examined how cortical excitation can help to improve auditory processing, the role of evoked inhibition across the cortex has been mostly overlooked."
Dr. Liu and colleagues designed a study that took advantage of the fact that mouse pups emit ultrasonic whistles that are recognized as behaviorally relevant by mother mice but not by pup-naÃÂ¯ve virgins. The researchers examined how neural responses could contribute to the detection of pup isolation calls by performing electrophysiological recordings from cells in the auditory cortex of fully awake mother or virgin mice. This is the first time that this type of study was performed on nonanesthetized animals.
Both mothers and virgins exhibited substantial call-evoked excitation and inhibition in response to the pup isolation calls. However, the inhibition started earlier and was longer, stronger, and more stereotypical in the mother mice. Importantly, the main changes in call-evoked inhibition occurred for neural areas that normally respond best to frequencies lower than the whistle-like calls of the pups. When these sites were tested with artificial tones of different frequencies, the greatest change in evoked inhibitory activity between mother and virgin mice was for pup call frequencies.
The findings demonstrate the importance of cortical inhibition in the maternal detection of species-specific vocalizations. "We hypothesize that the observed auditory cortical inhibitory plasticity improves pup call detection in the mother mice in a relatively specific manner by increasing the contrast between call-evoked responses arising from high-ultrasonic neural populations that should be excited, and so-called lateral band neural populations that should not be," concludes Dr. Liu. The authors suggest that this could have a benefit for detecting these calls in noisy backgrounds.
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