About 15% of the world’s population suffers from tinnitus, a condition that causes someone to hear a sound (such as a ringing or buzzing) without any external source. It is often associated with hearing loss.
The condition can not only be upsetting for those who suffer from it, but it can also have a serious effect on mental health, often causing stress or depression. This is especially the case for patients who suffer from tinnitus for months or years.
There is currently no cure for tinnitus. Therefore, finding a way to manage or treat it better could help millions of people around the world.
And one area of research that may help us better understand tinnitus is sleep. There are many reasons for this. First, tinnitus is a phantom perception. This is when our brain activity makes us see, hear or smell things that are not there. Most people only experience phantom perceptions when they are asleep. But people with tinnitus hear phantom sounds while awake.
The second reason is because tinnitus disrupts brain activity, with certain areas of the brain (such as those involved in hearing) potentially more active than they should be. This may also explain how phantom perceptions occur. When we sleep, the activity in these same areas of the brain also changes.
Our recent research review has identified a couple of brain mechanisms that underlie both tinnitus and sleep. Better understanding these mechanisms, and how the two are connected, could one day help us find ways to manage and treat tinnitus.
sleep and tinnitus
When we fall asleep, our body experiences multiple stages of sleep. One of the most important stages of sleep is slow-wave sleep (also known as deep sleep), which is believed to be the most restorative stage of sleep.
During slow-wave sleep, brain activity moves in distinctive “waves” through different areas of the brain, activating large areas (such as those involved with memory and sound processing) together before moving on to others. Slow-wave sleep is thought to allow the brain’s neurons (specialized brain cells that send and receive information) to recover from daily wear and tear, while also helping sleep make us feel rested. It is also believed to be important for our memory.
Not all areas of the brain experience the same amount of slow wave activity. It is most pronounced in areas that we use the most while we are awake, such as those important for motor function and vision.
But sometimes certain areas of the brain can be overactive during slow-wave sleep. This is what happens in sleep disorders such as sleepwalking.
Something similar can happen in people with tinnitus. We think that hyperactive regions of the brain could remain awake in the sleeping brain. This would explain why many people with tinnitus experience sleep disturbances and night terrors more often than people without tinnitus.
Tinnitus patients also spend more time in light sleep. In a nutshell, we believe that tinnitus prevents the brain from producing the slow-wave activity necessary for deep sleep, resulting in light, interrupted sleep.
But despite the fact that patients with tinnitus have less deep sleep on average than people without tinnitus, the research we discuss in our review suggests that deep sleep is barely affected by tinnitus. This may be because the brain activity that occurs during deeper sleep actually suppresses tinnitus.
There are a couple of ways the brain can suppress tinnitus during deep sleep. The first has to do with the neurons of the brain. After a long period of wakefulness, neurons in the brain are thought to switch to slow-wave mode of activity to recover. The more neurons that are together in this mode, the stronger the push for the rest of the brain to come together.
We know that the urge to sleep can become strong enough that neurons in the brain eventually go into slow wave mode of activity. And since this especially applies to hyperactive brain regions during wakefulness, we think tinnitus might be suppressed as a result of that.
Slow-wave activity has also been shown to interfere with communication between areas of the brain. During deeper sleep, when slow-wave activity is strongest, this can prevent overactive regions from disrupting other areas of the brain and disrupting sleep.
This would explain why people with tinnitus can still go into deep sleep and why the tinnitus can be suppressed during that time.
Sleep is also important for strengthening our memory, as it helps drive changes in the connections between neurons in the brain. We believe that changes in brain connectivity during sleep contribute to tinnitus lasting long after an initial trigger (such as hearing loss).
Treatment of tinnitus
We already know that the intensity of tinnitus can change throughout a given day. Investigating how tinnitus changes during sleep could give us direct insight into what the brain does to cause fluctuations in tinnitus intensity.
It also means we can manipulate sleep to improve patients’ well-being and possibly develop new treatments for tinnitus. For example, sleep interruptions can be reduced and slow wave activity can be boosted through sleep restriction paradigms, where patients are told to only go to bed when they are truly tired. Increasing sleep intensity could help us better see the effect sleep has on tinnitus.
While we suspect that deep sleep is more likely to affect tinnitus, there are many other stages of sleep that occur (such as rapid eye movement or REM sleep), each with unique patterns of brain activity. In future research, both sleep stage and tinnitus activity in the brain could be tracked at the same time by recording brain activity. This can help learn more about the link between tinnitus and sleep and understand how natural brain activity can relieve tinnitus.