Over-exposure to irrelevant sounds can cause the brain to tune them out in favor of other auditory stimuli, reports a study in the July issue of Nature Neuroscience. This finding is surprising because previous work has suggested that exposure to certain sounds increases the brain's response to them.
The authors exposed adolescent cats to random sequences of tones whose frequency varied within a fixed range, and then looked at the neural responses to the different frequencies in the cats' auditory cortex. Following exposure, which lasted 24 hours a day for about 5 months, neurons in the cats' auditory cortex showed much weaker responses to frequencies that had been present in the exposure stimulus. In contrast, responses to other frequencies were enhanced. The results suggest that overexposure to a stimulus can impair its representation in the brain.
The auditory stimulus in this case was of no relevance to the cats, and presumably was ignored. It remains to be seen what would happen with overexposure of behaviorally relevant stimuli.
Jos Eggermont (University of Calgary, Canada)
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Abstract available online.
(C) Nature Neuroscience press release.
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