Julie Raney is a certified and licensed audiologist. She has a B.S. in Communication Sciences and Disorders and a Master’s Degree in Audiology from Idaho State University. She has worked as a clinical audiologist in Colorado since 2005. She specializes in hearing amplification for adults and delivers her services in both English and Sign Language.

Understanding Sleep Stages

To understand what happens to hear while sleeping, it is useful to know more about sleep stages. Though we commonly think of sleep as one long duration of rest, it actually consists of sleep cycles. Each sleep cycle is made up of four phases and on an average night, we experience 4 – 6 sleep cycles. Sleep stages include the following:

Stage 1: this first phase of sleep is the period between being awake and falling asleep. It is characterized by dozing off, the body starts to relax, and the brain slowing down. This stage is usually the first 1-5 minutes of initiating sleep.
Stage 2: sleep really starts during this stage. Heart rate, body temperature, breathing, and brain waves slow down and you become more unaware of your surroundings. While it’s easier to wake up during stage 1, it is more difficult to wake up from stage 2. This stage is 10 to 25 minutes, becoming longer as sleep progresses through the night.
Stage 3: this is the deepest sleep stage involving a greater decrease in breathing and heart rate. This sleep stage is critical for replenishing and restoring the systems that sustain the body. Hormones are released, healing takes place, and the body is provided with energy. This stage can last 20 to 40 minutes, getting shorter as sleep continues.
Stage 4: the last sleep stage is REM (rapid eye movement) sleep. The brain becomes more alert and active. Our most vivid dreams happen during this state which also involves the eyes moving back and forth while still closed. REM sleep makes up nearly 25% of your sleep cycle.

On average, a sleep cycle lasts 90 minutes. Adults need 7- 9 hours of sleep each night which would mean experiencing 5 to 6 sleep cycles. Sleep stages provide the body with the time and space to rest and replenish which is critical for metabolism, mood, healing, cognitive performance, etc.

Hearing While Sleeping

Though it was previously assumed that after falling asleep, your brain shut off and you didn’t hear anything in your surrounding environment; emerging research is showing otherwise. Recent studies highlight that you can actually hear during sleep. This includes a 2019 study published in the Human Nature Behavior Journal. Researchers assessed how the brain responds to external sound during sleep by exposing participants to different voices as they slept. They did this by replicating the “cocktail party problem” which refers to our capacity to hear multiple voices simultaneously but choosing which voice to focus on. This is what enables people to hear and have a conversation in environments with background noise.

Researchers played two different voices, one in each ear, through headphones that participants wore while sleeping. One voice communicated clear sentences while the other expressed incoherent phrases. While participants were being exposed to these sounds, researchers captured brain activity through EEG recordings. After analyzing the data, researchers sound that the brain was in fact alert and following the sounds that were clearly expressed. More attention was given to the clear sentences compared to the incoherent phrases.

This study shows that the brain does pay attention to and absorbs external sounds during sleep which is more likely to occur during the first two stages of the sleep cycle. Though you may not remember the specific sounds or speech you heard the following morning, your brain can and does track this sound. In this way, it is similar to dreaming where you may not remember the details of your dreams but you do know that you did dream.

Prioritize Your Hearing Health Today

Knowing that the brain is alert during some phases of sleep is fun information to learn! Having a hearing loss can reduce this capacity so tending to hearing health is important. You can call us today to schedule an appointment for a hearing test! Hearing tests are a painless process that assesses and measures your hearing capacity in both ears. This establishes your hearing needs and allows us to make effective recommendations to meet those needs. Get started today by calling us to schedule your first appointment!