Hyperactivity Linked to Inner Ear Defect When hyperactivity is found in children with severe hearing loss, it is often assumed to stem from frustrations they have communicating or socializing. But a new study says a genetic defect in the inner ear may also play a role in causing hyperactive behavior, suggesting that at least in some cases, hyperactivity can have a neurobiological root. Researchers at the Albert Einstein College of Medicine in the Bronx caused inner-ear defects in young mice by knocking out a gene called Slc12a2, causing a loss of hearing and sense of balance. But the removal of the gene also resulted in higher levels of two proteins, pERK and pCREB, in the striatum, a part of the brain that helps regulate motor functions. The mice then displayed hyperactive behavior, like running rapidly in a circle. Suspecting that the higher protein levels were causing the behavior, the researchers lowered them. With normal levels of pERK and pCREB restored, the mice's behavior returned to normal. Precisely which neural pathway from the ear to the brain was active in this case is not yet clear, said the study's lead author, Jean M. Hébert, a neuroscientist at the Albert Einstein College of Medicine. "Is it the activation of the normal neural network that is causing the increase in these proteins and this behavior?" he said. We haven't checked that yet. He also noted that the study, which was published Friday in the journal Science, potentially identified only a single source of hyperactivity, which is likely to have many causes. "I wouldn't start having hyperactive kids tested for their hearing," he said.