Hyperactivity May be Caused by Inner Ear Defects, Researchers Say

Researchers say the source of hyperactivity among children may originate in the inner ear, according to a study published on Friday.

In a new study, published in the journal Science, scientists at Albert Einstein College of Medicine of Yeshiva University found that inner-ear dysfunction in mice caused neurological changes which led to hyperactivity.

The researchers noted that many children and teenagers with severe disorders affecting hearing and balance also suffer from behavioral problems such as hyperactivity. This is the first study to confirm the link between the two.

"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 lead researcher Professor Jean Hebert, from the Albert Einstein College of Medicine in New York City.

The genesis of the research occurred when researchers discovered that deaf laboratory mice with severe inner ear defects were also curiously hyperactive compared to mice without the ear defects.

The animals' inner ear problems were caused by a defective gene, called Slc12a2, affecting the transport of sodium, potassium and chloride molecules in various tissues, including the central nervous system. The researchers also said that humans possess the gene.

In order to see if test a link existed between the gene mutation and with the animals' hyperactivity, the scientists selectively deleted the Slc12a2 from either the inner ear, various parts of the brain that control movement or the entire central nervous system of healthy mice.

"To our surprise, it was only when we deleted the gene from the inner ear that we observed increased locomotor activity," Hebert said.

"It certainly raises the issue that we ought to critically consider what contributes to the links between sensory impairments and specific behaviors/disorders," said Anita Thapar, professor of child and adolescent psychiatry at Cardiff University's Institute of Psychological Medicine and Clinical Neurosciences.

"ADHD, like most neuropsychiatric and medical disorders, is not caused by a single mutation.

"On the other hand animal models allow for experimental manipulation in a way that cannot be achieved in humans and the results can help shape hypotheses to test in humans."