A new study has found that inner-ear dysfunction can directly cause neurological changes that increases hyperactivity.
The study, conducted in mice, also implicated two brain proteins in this process, providing potential targets for intervention.
For years, scientists have observed that many children and adolescents with severe inner-ear disorders - particularly disorders affecting both hearing and balance - also have behavioral problems, such as hyperactivity.
Until now, no one has been able to determine whether the ear disorders and behavioral problems are actually linked.
"Our study provides the first evidence that a sensory impairment, such as inner-ear dysfunction, can induce specific molecular changes in the brain that cause maladaptive behaviors traditionally considered to originate exclusively in the brain," study leader Jean M. Hebert, Ph.D., professor in the Dominick P. Purpura Department of Neuroscience and of genetics at Albert Einstein College of Medicine of Yeshiva University, said.
The inner ear consists of two structures, the cochlea (responsible for hearing) and the vestibular system (responsible for balance).
Inner-ear disorders are typically caused by genetic defects but can also result from infection or injury.
The idea for the study arose when Michelle W. Antoine, a Ph.D. student at Einstein at the time, noticed that some mice in Dr. Hebert's laboratory were unusually active - in a state of near-continual movement, chasing their tails in a circular pattern.
Further investigation revealed that the mice had severe cochlear and vestibular defects and were profoundly deaf.
The findings are published in the online edition of Science.
