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Very noisy homes could put the mental development of babies at risk. New research indicates that constant background noise may swamp an infant's brain, holding back its ability to recognize sounds. These findings may explain why language-learning disorders have increased over the last few decades.
Scientists from the University of California at San Francisco published a study in Science that describes that young rats reared in an environment of moderate continuous noise did not harm hearing but a generated "white noise" that was able to mask normal sounds. Generally the auditory cortex, in a growing rat's brain undergoes swift and radical reorganization. The neurons cluster into a smaller area, and become more tuned into different pitches and patterns of sound. The researchers found that in rats exposed to the white noise, the auditory cortex took three or four times longer than normal to mature. Additional tests on the maturing noise-reared rats showed that their auditory regions continued to be plastic — they continued to reorganize their neural circuitry in response to exposure to sound stimuli alone, long after the brains of normal rats had ceased rewiring. This suggested that a “critical period” for exposure-based plasticity in the brain had been extended.
Although the findings involve rats, they are likely to apply to humans since all mammals share similar basic patterns of brain development. These findings suggest that environmental noise, which is commonly present in contemporary child-rearing environments, can potentially contribute to auditory and language-related developmental delays. Future studies by the research team will address whether humans with developmental disorders have higher levels of noise in their auditory systems. Such studies could lead to diagnostic and predictive tests.
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