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As we drift off to sleep, we lose conscious awareness of what’s happening around us. But certain sounds can wake us up. From a snoring partner to traffic noise out the window, noise can wake us from deep sleep. So our ears and brain must continue processing sounds even when we’re asleep. How does this work exactly, and what can we hear while sleeping?
The Stages of Sleep
Our brains respond differently to external stimuli depending on which stage of sleep we’re in. For example, when you’re in light sleep, you are more likely to hear noises around you, and more likely to wake up. But when you’re in deep sleep, you probably won’t hear much.
Here are the stages of sleep:
- Light sleep – During light sleep, you drift slowly to sleep. You’re still partially paying attention to things in your environment, and you can easily wake up at a soft sound. When you have a short nap, you probably don’t go deeper than light sleep.
- Deep sleep – During deep sleep, or slow-wave sleep, the brain disconnects from the outside world. You are less likely to hear external sounds or be disturbed by noises in the environment. During this sleep stage your brain consolidates memories from the day, and stores memories in long term memory. You will still maintain a slight awareness of the outside world. This is adaptive, since our ancestors still needed to keep somewhat alert to any threats from the outside world.
- REM sleep – During REM or Rapid Eye Movement sleep, you often start dreaming. All the brain activity paused in deep sleep starts again as you start to dream. However, you still do not process exterior sounds during this stage.
What Do You Hear While Sleeping?
A 2016 study took a close look at how the brain processes sounds while you’re sleeping. They found that during light sleep, such as during short naps or when you’re first falling asleep, you are still processing the things you’re hearing. You can even hear and process words that you hear while you’re in light sleep.
EEG readings of sleeping participants showed that during light sleep, the participants’ brains were still responding to words, and were continuing the verbal recognition tasks they started when awake. They were able to hear and process new words even while sleeping!
As you transition into deep sleep, however, you stop processing external sounds. And that’s not all. When you’re in deep sleep, your night’s rest may even erase from memory whatever sounds you heard when you were in light sleep. Once the participants transitioned into deep sleep, their brains stopped processing words. The brain started ignoring the external sounds and began resting deeply.
When participants transitioned to REM sleep, they still didn’t seem to hear the external sounds, even though they had increased brain wave activity. During REM sleep focus stays inwards, and participants focus on their internal dreams rather than on outside sounds.
Our Brains Are Listening While We Sleep
For a long time, scientists thought that the brain shut down during sleep, and didn’t process anything happening in the external world. But now researchers are discovering what really happens. While it’s true that during some sleep stages our brains pay very little attention to what’s happening around us, during other stages we’re able to hear and process sounds even in our sleep.
Not only that, but we are listening for certain sounds while we sleep, even when we’re in deep sleep. For example, we grow accustomed to the sounds that usually fill our home during sleep. This includes the hum of the fridge, or the heating or cooling system turning on and off. But as soon as there’s a strange sound, we wake up almost immediately. Was there something rustling outside? Did one of the kids just get up? Who’s having a snack in the kitchen? These sounds are considered relevant sounds, and the brain pays attention to these sounds even during sleep.
Do You Have Hearing Loss?
If you have hearing loss, you will have a hard time hearing. You won’t be able to hear words when you’re awake, let alone when you’re sleeping. Find out more about your hearing health by visiting us for a hearing test. Find out what sounds you’re missing, and explore your treatment options today!