The high noise of modern life may affect speech and language development in the very young, according to a study that found the auditory   parts of the brains of young mice are slower to organize properly in the presence of continuous sounds. Researchers at the University of California, San Francisco, reared a group of rats in an environment of continuous background noise and found that their brain circuits that receive and interpret   sound did not develop at the same rate as animals that were raised in a quieter environment. Edward F. Chang and Michael Merzenich, co-authors of the study appearing in the journal Science, said that the continuous noise delayed the organization of auditory neurons   during a critical two-to-three-week period after the rat pups were born. For rats not exposed to the noise, the auditory cortex  neurons during this period gathered into a smaller area and began developing a selective response to sounds. But for the noiseexposed rats, this organization was slowed, causing a delay in the development of the ability to discriminate  specific sound tones. The researchers said it took three or four times longer for the rats raised in a noisy environment to reach the basic bench marks   of auditory development seen in the rat pups not exposed to noises. Although the rat is not a perfect model for what happens in humans, the authors note, the study does suggest that high levels of noise might possibly affect some language learning in babies. "These findings suggest that environmental noise, which is commonly present in contemporary child-rearing environments, can potentially contribute to auditory and language-related development delays,"the authors wrote in Science. The authors noted that although the brain development was delayed in rats exposed to the noise, their brains did eventually mature   normally. The rats exposed to noise, compared to those not exposed,   _  .
were more sensitive were duller grew up more slowly gathered together more quickly