Exposure to noise during the first months of life could impair a child's hearing and lead to a learning disability, says medical student Edward Chang of the University of California at San Francisco. He and his adviser, neuroscientist Michael Merzenich, exposed newborn rats to continuous white noise for up to three months. The researchers then anesthetized the animals and probed their brains. The rats showed a significant lag compared with the control group. "The basic shape of the auditory cortex was slower to develop, and the response properties of individual neurons were also delayed," Chang says. Overall, the noise-exposed rats' brains matured as slowly as one-fourth the normal rate.
Human hearing development resembles that of rats in many ways. The researchers therefore worry about children growing up in noisy environments, such as near airports or busy highways. "In humans, delays in development can be severe. Many kids with learning problems eventually catch up, but the rate at which they do is slower," Chang says. He and Merzenich are trying to identify children who, because of genetics or physiology, are especially susceptible to noise-related hearing loss. "Then we could recommend if a kid needs an enriched, special environment."