Hyperactivity in children may originate in the inner ear, new research suggests.
Scientists have evidence that inner-ear disorders can trigger the neurological changes underlying the behavioural condition.
Two brain proteins are thought to be involved that could provide targets for new treatments.
Many children and teenagers with severe disorders affecting hearing and balance also suffer from behavioural problems such as hyperactivity.
Until now no one has been able to determine for certain if the two are 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 behaviours traditionally considered to originate exclusively in the brain,” said lead researcher Jean Hebert, from the Albert Einstein College of Medicine in New York City.
The investigation began after it was discovered that profoundly deaf laboratory mice with severe inner ear defects were also unusually active.
The animals’ inner ear problems were caused by a defective gene affecting the transport of sodium, potassium and chloride molecules in various tissues, including the central nervous system.
Humans also possess the gene, said the researchers whose findings are reported in the journal Science.
When the gene was “knocked out” from the inner ears of healthy mice, the animals became hyperactive.
To the surprise of the scientists, this only happened when the gene was deleted from the inner ear. The same effect was not triggered by knocking it out of the brain or spinal cord.
Tests revealed a role played by two proteins controlling nerve signalling chemicals, or neurotransmitters. Suppressing one of them with a specific drug restored activity levels to normal.
“Our study also raises the intriguing possibility that other sensory impairments not associated with inner ear defects could cause or contribute to psychiatric or motor disorders that are now considered exclusively of cerebral origin,” said Hebert.
“This is an area that has not been well studied.”