In decades past, experts believed that sleep was akin to us going offline. It was thought of as a non-active state where not much was happening. More recent scientific findings paint quite a different picture. For instance, brain activity during sleep actually increases while our bodies rest.
Now, researchers have found that the brain hears quite a bit of what’s happening outside of us as we sleep, which might not be news to light sleepers. Kidding aside, new data gives us insight into how listening works and the ways our brains are attuned to noise.
Much of hearing happens in the brain
When we think about hearing during sleep, it comes as no surprise that we cannot turn our ears ‘off.’ And while the body is resting, using sleep as a means to recover and repair, it seems that the tissues and cells of the inner ear continue to receive sound, as they do when we are awake.
During the hearing process, the ear acts as the perfect architecture to funnel sound, directing it to the inner ear. Tiny, sensitive cells within the inner ear collect this noise and translate it into sound information — in the form of electrical signals. Those signals travel to the brain via the auditory nerve, where the brain’s processing centers decode the sound information and turn it into meaning. Due to the power and dexterity of our brain’s processing centers, this process is instantaneous and unconscious.
Response to sound during sleep
But the way the brain reacts to noise during sleep appears to be slightly different from our conscious, or waking, life. One French study seems to suggest that our brain uses a function typically employed in large gatherings or group settings.
In one ear, sleeping participants were played a recording in which a person articles or movie dialogue. In the other ear, they played recitations in Jabberwocky, a nonsense language. Rather than ignoring all sensory hearing information, the brain did tune into what it was hearing. However, the caveat is that the sound has to be important or appear significant in order for the brain to pay attention. In this particular study, analysis of brain activity showed that the brains of the slumbering cohort exponentially preferred language that was meaningful.
“If there is one thing that cognitive sciences have shown time and time again, it’s that our brains are tuned to process meaning,” says Dr. Thomas Andrillon Ph.D., a research fellow at Monash University in Australia and an author of the study.
The cocktail party effect
The ear itself isn’t choosing what voices or sounds to focus on. Instead, it sends all of that sound information to the brain to sort though. Have you ever been in a large gathering and heard someone mention your name, even if they’re physically distant from you? It can happen even as you are following a conversation happening right in front of you. The brain’s ability to filter important sounds, like the sound of your name or the person you’re talking to, and ignore other ‘noise’ is called the cocktail party effect.
It’s almost as if the brain has volume levels it can adjust for our attention.
What do we do with the sounds we hear during sleep?
A separate study from Tel Aviv University used deeply placed electrodes to measure brain activity during sleep. They found that the brain responds similarly to noise in both wakefulness and while sleeping with one exception. During sleep, alpha-beta waves were different in a way that suggests the brain hears and analyzes sound information, yet does not have the capacity to identify the sound or even zoom in on it. Instead, the study’s authors found that conscious awareness was not present during sleep in relation to sound.
Therapeutic use of noise during sleep
There are currently non-scientific therapies that rely on the brain’s attention during sleep. Some people listen to meditations or affirmations while they sleep because they believe that way provides access to the unconscious mind.
Some of us might not be able to tap into the unconscious filtering system as easily or regularly as others. This can explain why some of us identify as light sleepers. If you find that external noises regularly interrupt your sleep, it may be that you need to add a buffer for your brain. Try playing white noise as you sleep or another ambient sound.