Could hyperactivity be linked to poor HEARING? Scientists discover that inner ear problems and restlessness are caused by the same faulty gene
- Ear defects cause abnormal function in brain area that controls movement
- Mice with gene mutation that causes inner ear defects were found to be more prone to hyperactivity
- When the gene was ‘deleted’ from their inner ear, hyperactivity decreased
- Humans also have the same gene so findings could apply to us as well
- Increased levels of two proteins also contribute to hyperactivity – when these proteins are inhibited, activity levels return to normal in mice
- The findings could lead to new treatments for hyperactivity in children
By Emma Innes
Behavioural abnormalities are traditionally thought to originate in the brain, but researchers have found that inner ear dysfunction can directly cause neurological changes
Abnormalities in the inner ear could lead to hyperactivity, a study has found.
Behavioural abnormalities are traditionally thought to originate in the brain, but researchers have found that inner ear dysfunction can directly cause neurological changes.
This could mean that hyperactivity in children with inner ear disorders might be controllable with medication that tackles the related area of the brain.
For years, scientists have noted that many children and adolescents with severe inner ear disorders – particularly disorders affecting both hearing and balance – also have behavioural problems, such as hyperactivity.
But until now, no one has been able to determine whether the two 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 behaviours traditionally considered to originate exclusively in the brain,’ said study leader Dr Jean Hebert, a professor at the Albert Einstein College of Medicine in New York.
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 came about when a Ph.D. student at Albert Einstein College of Medicine noticed that some mice in Dr Hebert’s laboratory were in a state of near-continual movement, chasing their tails.
Further investigation revealed they had severe problems with their ears and were profoundly deaf, reports the journal Science.
The researchers established that the animals’ inner ear problems were due to a mutation in a gene which is also found in humans.
To determine whether the mutation was linked to the animals’ hyperactivity, the scientists took healthy mice and selectively deleted the gene from either the inner ear, various parts of the brain that control movement or the entire central nervous system.
‘To our surprise, it was only when we deleted the gene from the inner ear that we observed increased [movement],’ said Dr Hebert.
As a result of their findings, the researchers suggest that inner ear defects cause abnormal functioning of a central brain area that controls movement.
Tests revealed increased levels of two proteins involved in a signalling pathway that controls the action of neurotransmitters.
The increased levels were only seen in the central area of the brain controlling movement, and not in other forebrain regions.
To discover whether this caused the abnormal increase movement, the mice that had the gene removed were given an injection to inhibit the protein.
This resulted in activity returning to normal.
According to the researchers, the findings suggest that hyperactivity in children with inner ear disorders might be controllable with medications that directly or indirectly inhibit the same pathway in the central area of the brain.
‘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 Dr Hebert.