'Rebooting' brain may ease tinnitus
2011-01-13 09:26
Washington - Scientists have found a way to ease chronic ringing in the ears, known as tinnitus, by stimulating a neck nerve and playing sounds to reboot the brain, according to research published on Wednesday.
There is currently no cure for tinnitus, which can range from annoying to debilitating and affects as many as 23 million adults in the US, including one in 10 seniors and 40% of military veterans.
For Gloria Chepko, 66, who has had tinnitus since she was 4 years old, the sound she describes as "like crickets... but also bell-like," gets worse when she is tired.
"It's awful," she said. "Sometimes it is very loud, and it will get loud if I am under stress or if I have been going for a very long time and I am fatigued," she said. "If my mind is tired and I sit down I will only hear this sound."
For some people, such as military veterans who are left with hearing damage after exposure to loud blasts and gunfire, the noise - which could also sound like roaring, whooshing or clicking - interferes with their ability to lead a normal life.
Nerve damage
The US Veterans Administration spends $1bn per year on disability payments related to tinnitus, the most common service-related ailment in soldiers returning from Iraq and Afghanistan, industry experts said.
Scientists believe the disorder is caused by hearing loss or nerve damage, to which the brain tries but fails to adjust.
"Brain changes in response to nerve damage or cochlear trauma cause irregular neural activity believed to be responsible for many types of chronic pain and tinnitus," said Michael Kilgard of the University of Texas, co-author of the study in the journal Nature.
"We believe the part of the brain that processes sounds - the auditory cortex - delegates too many neurons to some frequencies, and things begin to go awry," he said.
To fix that, researchers used rats to test a theory that they could reset the brain by retraining it so that errant neurons return to their normal state.
In rats with tinnitus, they electrically stimulated the vagus nerve, which runs from the head through the neck to the abdomen, in combination with playing a certain high-pitched tone.
When stimulated, the nerve can encourage changes in the brain by releasing chemicals such as acetylcholine and norepinephrine that act as neurotransmitters.
Reorganised neurons
Rats that underwent the pairing of noise and stimulation experienced a halt to the ringing sounds for up to three and a half months, while control rats that received just noise or just stimulation did not.
An examination of neural responses in the auditory cortexes showed normal levels in the rats which were treated with the combination of stimulation and sound, indicating the tinnitus had disappeared.
The treatment "not only reorganised the neurons to respond to their original frequencies, but it also made the brain responses sharper", the study said.
"The key is that, unlike previous treatments, we're not masking the tinnitus, we're not hiding the tinnitus," said Kilgard.
"We are returning the brain from a state where it generates tinnitus to a state that does not generate tinnitus. We are eliminating the source of the tinnitus."
Clinical trials are expected to begin on humans in the coming months, with the first trials starting in Europe, according to lead study author Navzer Engineer.
The process of vagus nerve stimulation, known as VNS, is already being used in the treatment of around 50 000 people with epilepsy or depression, the study said.
Damaged circuits
"This minimally invasive method of generating neural plasticity allows us to precisely manipulate brain circuits, which cannot be achieved with drugs," said Engineer.
"Pairing sounds with VNS provides that precision by rewiring damaged circuits and reversing the abnormal activity that generates the phantom sound."
Like many sufferers, Chepko has learned to cope with the noise.
"I have to find some other way to relax to just endure it, take a bath or do stretches or just lie down and stare or read a book, depending on how bad it is," she said.
"I have kind of lived around it, or over it."