"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."
Behavioral abnormalities are traditionally thought to originate in the brain. But a new study by researchers at Albert Einstein College of Medicine of Yeshiva University has found that inner-ear dysfunction can directly cause neurological changes that increase hyperactivity. The study, conducted in mice, also implicated two brain proteins in this process, providing potential targets for intervention. The findings were published today in the online edition of Science.
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," said study leader Jean M. Hébert, Ph.D., professor in the Dominick P. Purpura Department of Neuroscience and of genetics at Einstein.
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. Hébert'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. "We then realized that these mice provided a good opportunity to study the relationship between inner-ear dysfunction and behavior," said Dr. Hébert.
The researchers established that the animals' inner-ear problems were due to a mutation in a gene called Slc12a2, which mediates the transport of sodium, potassium, and chloride molecules in various tissues, including the inner ear and central nervous system (CNS). The gene is also found in humans.
To determine whether the gene mutation was linked to the animals' hyperactivity, the researchers took healthy mice and selectively deleted Slc12a2 from either the inner ear, various parts of the brain that control movement or the entire CNS. "To our surprise, it was only when we deleted the gene from the inner ear that we observed increased locomotor activity," said Dr. Hébert.
Category(s):Inattention, Impulsivity, & Hyperactivity (ADHD)
Source material from Albert Einstein College of Medicine
