“HAVE you signed the card for aunt Alice?”, my wife asked one morning. But what I heard was: “Have you signed the contracts?” “There’s a cross breeze,” she told me when a gale blew through an open window. There’s a what? A crossbow? A cross-breed?
Conversations like this are common in our household. I also struggle to hear people in a noisy room or over a bad phone line. I finally knew I needed help when my wife spoke to me from another room and I was unable to decipher a single syllable. She might as well have been one of the adults in the Peanuts cartoons, saying “Mwah-mwah-mwah…”
I am far from alone. I am 56, and roughly a tenth of people my age have the same problem – an impaired ability to hear speech against background noise. Add 10 years and it’s up to 20 per cent. It’s not as if somebody has dialled down the volume. We hear the sounds; we just can’t pick out the words.
But here’s the catch. I’ve had my hearing tested three times in the last decade, and the results always come back normal. “We call it hidden hearing loss, because it hides behind the audiogram that is the gold-standard test of hearing,” says Charles Liberman, a neuroscientist at Massachusetts Eye and Ear Infirmary in Boston. It’s also hidden because the problem isn’t in the ears at all; it’s in the most important hearing organ: the brain.
The idea that the brain is behind this kind of hearing loss opens up a whole new way of treating it. Instead of cranking up the volume with a hearing aid, why not train the brain to process the ear’s signals better? A number of computer programs now promise to enhance the brain’s auditory machinery from the comfort of your home. Curious and a little sceptical, I had to try it.
To understand how such an idea might work, let’s start with what happens to our hearing as we age. We are born with about 11,000 hair cells in each ear. These delicate cells convert sound waves to electrical signals, but they are easily damaged by ageing and excessive noise. Hearing aids and cochlear implants are designed to treat this kind of impairment, and they can be very successful.
But in recent years, Liberman and his colleagues have turned their attention to the next step in sound processing – the auditory nerve fibres that pass the hair cells’ signals to the brain. Their work has revealed that loud noises can cause a shocking amount of damage to these nerves (see “Silent epidemic“). More specifically, it’s the connections, or synapses, between the hair cells and the auditory nerves that are destroyed, a problem known as synaptopathy. The hair cells themselves remain.
Synaptopathy doesn’t show up in audiograms because these only test the effect of hair-cell loss. “The whole domain of hearing assessment has systematically ignored the fact that the brain is a participant,” says Michael Merzenich, a neuroscientist and creator of a brain-training program called BrainHQ. Perversely, the nerve fibres that are most damaged by noise are those we rely on to understand speech in a noisy environment – up to 90 per cent of these synapses can be damaged, yet you can still perform normally in a hearing test.
The loss of these connections means the brain processes sounds more slowly and samples them more infrequently, which makes it much harder to decipher different letters, especially those that sound similar. “We’ve called this problem by many names, but we’ve never really understood it,” says Kelly Tremblay, an audiologist at the University of Washington in Seattle. “Liberman’s work has for the first time provided an explanation. That opens the door to new treatments.”
In particular, because the nerve and hair cells are still alive, it may be possible to persuade them to grow new connections. Liberman has managed to restore these synapses in mice using a drug called dexamethasone, although the side effects are still too severe for it to be used in people. Several pharmaceutical companies are also developing medications to restore hearing.
If, like me, you can’t wait, there is an alternative.
The idea of brain training for better hearing came to my attention in a 2013 paper by Nina Kraus and colleagues at Northwestern University in Illinois. They showed that people who did 40 hours of BrainHQ training over eight weeks had significant improvements to the first layer of auditory processing in the brain, which occurs in the brainstem. Their neural responses to sounds became quicker, and they became better at picking out speech in background noise compared with a control group who used general education software.
Intrigued by the promise of hard science to back up the concept, I got in touch with Merzenich, who agreed to provide me with the same training exercises. Kraus, who has no connection to Merzenich’s company, offered to perform the same independent before-and-after testing that she had done in her study.
After my initial tests, for two months I spent around an hour, five days a week, at the computer learning to pick out target sounds from others that sound similar, for example.
Much has been made in recent years of the idea that “brain-boosting” software may provide a mental workout that could fine-tune our neural faculties, but there have been mixed results under scientific scrutiny. What about hearing?
The very origins of the idea of brain plasticity – that the brain can rewire itself in response to how we use it – lie with the first cochlear implants that were tested in people in the 1980s. They were unexpectedly successful.
A cochlear implant delivers much less information to the brain than a healthy ear. When the implant is first turned on, this impoverished signal sounds very strange to the user. Yet after a year, people report that they can hear just like they used to.
That’s because the brain adapts itself to the new information if it receives feedback. “Synaptic inputs strengthen if they contribute to getting the answer right,” says Merzenich. This rewiring only works if the brain knows when it’s right. This might help explain the hearing improvements Kraus saw in her study. BrainHQ and similar programs are designed to be adaptive – the difficulty changes based on how someone is doing – and they provide immediate feedback.
After 40 hours of training, I returned to Kraus’s lab for evaluation. I was particularly curious about the auditory brainstem response (ABR) test, because it looks at those very earliest stages of auditory processing in the brain. If you are looking for synaptopathy, that’s where you will find it. Kraus also considers it a snapshot of overall brain health.
In my case, it’s good news. My ability to perceive sentences in background noise improved substantially. Before training, I could only pick out target sounds if they were at least 1.75 decibels louder than the background (see diagram), but after training I could pick out just sounds 0.5 dB louder. “It’s as if the mixing board in your brain has turned down the noise knob by 1.25,” Kraus says. To put that in context, a 1 dB improvement increases intelligibility of approximately 10 to 15 per cent of the words.
So my test scores improved significantly, but did this translate into real improvements in my day-to-day hearing? The main criticism levelled against brain training is that even when there are improvements in a test situation, the real-world effects can be disappointingly small.
Confidence boost
I can say there was no “eureka” moment when my hearing suddenly improved. I still misunderstand conversations. And yet the training did give me confidence. I realised I had developed a learned helplessness, always asking “what?” when I didn’t understand something. The exercises broke that cycle. During training you have to answer, and the software sets the difficulty so that your guess will be right more often than not. This gave me the confidence to guess in real life.Whether this kind of improvement is enough to justify investing in auditory brain- training software is for affected individuals to decide. You will probably need to keep at it to maintain any gains, and not everyone will see improvements. But the confidence boost could be worth it.
“I don’t think we have evidence at this point to state that this will help everybody, so as a scientist I can’t endorse it,” says Tremblay. “But as a clinician, I think that if somebody feels they are gaining benefits from it, and it motivates them to work with their auditory system and become a better listener, then I would encourage that.”
There may be cheaper and more enjoyable ways to work on that system, too. Kraus has found that musicians are protected from some effects of age-related hearing loss. In tests to pick out speech from background noise, musicians have the performance of somebody 20 years younger, probably because listening carefully to subtleties in music trains the same abilities.
Tuning in to different kinds of audio could also help. As Tremblay puts it, your auditory system, just like your body, needs exercise. “Whether it’s books on tape, or a computer-based training experience, taking advantage of sound and using your own faculties is always a good thing.”
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