Direct probing of brain reveals multiple regions cause tinnitus
Constant ringing in your ear? Scientists may be able to identify the cause of tinnitus, after peeking inside the brain of a man with the condition for the first time.
Tinnitus is the debilitating sensation of a high-pitched noise without any apparent source. It can be permanent or fleeting, and affects at least 25 million people in the US alone.
To understand more about the condition, William Sedley at the University of Newcastle, UK, and his colleagues took advantage of a rare opportunity to study brain activity in a man with tinnitus who was undergoing surgery for epilepsy.
Surgeons placed recording electrodes in several areas of his brain to identify the source of his seizures. The man – who they knew as Bob (not his real name) – was awake during the procedure, which allowed Sedley’s team to manipulate his tinnitus while recording from his brain.
First they played him 30 seconds of white noise, which suppressed his tinnitus for about 10 seconds before it gradually returned. Bob was asked to rate the loudness of his tinnitus before the experiment started, as well as immediately after the white noise finished and 10 seconds later. This protocol was then repeated many times over two days.
“Normally, studies compare brain activity of people with and without tinnitus using non-invasive techniques,” says Sedley. “Not only are these measurements less precise, but the people with tinnitus might be concentrating on the sound, while the ones without tinnitus might be thinking about their lunch.” This, he says, can make the results hard to interpret.
“What was nice about our experiment was that we could compare the brain activity associated with loud and quiet tinnitus without anything like attention or emotion muddying the waters,” he says.
High alert
Sedley’s team discovered that several kinds of brainwave associated with tinnitus were much more widespread than previously thought.
For example, Bob’s tinnitus was associated with more activity than normal in the primary auditory cortex – an area of the brain involved in the initial processing of sound – but also in other brain areas involved in the wider perception of noises, such as those that control attention, memory and emotion.
Working out why some people get tinnitus and others don’t is tricky, says Sedley. But there is some evidence of excessive amplification of sound in people with tinnitus, with the brain perceiving sounds that wouldn’t normally enter one’s consciousness.
“It’s like when you’re walking home on a dark night and you can hear every little flicker of sound that would normally go unnoticed,” says Sedley. “Maybe in people with tinnitus, this ‘high alert’ activity somehow kicks in, gains access to wider perception networks in the brain, and is difficult to dislodge.”
Noise reduction
Some treatments, such as nerve-stimulation devices that attempt to retrain the brain, can be effective for a small minority of people, but there is no real cure.
“What has held back treatments is that we don’t know what we’re trying to target,” says Sedley. “We would hope that a better understanding of the brainwaves that underlie tinnitus might help to refine or inspire new treatments.”
One frustration in researching a subjective sensation such as tinnitus is an inability to directly analyse the neural activity of the perception in humans, says David Baguley, a consultant clinical scientist at the Cambridge University Hospitals NHS Foundation Trust.
He says that Sedley’s team has undertaken a hugely innovative study, and while the work needs considerable discussion and independent corroboration, “it potentially represents a major development of understanding of tinnitus in the auditory brain”.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2015.02.075
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