The One Body Part That Never Goes To Sleep

According to the National Sleep Foundation, almost every part of the body experiences significant changes during sleep. When we fall asleep, sleep signals are sent throughout the body as thousands of neurons in the brain shift from the waking to sleeping state. Getting restorative sleep reinforces the cardiovascular and immune systems, helps regulate metabolism, consolidates memory, and allows the body to recover in general. Things like our breathing, muscle tone, heart rate, and hormone levels change considerably when sleeping.

But according to a study in Nature Human Behavior, sleeping is not an isolated activity. Slumberers go into "standby mode," where they can continue tracking relevant signals, maintaining the ability to "rapidly awake when necessary." It's how a new parent can wake instantly to the sound of their crying infant but ignore the din of traffic outside their window. Or how you can wake up to the sound of someone calling your name, but tune out other conversation. 

Researchers at Vanderbilt University studied the brainwaves of preschool-aged children to look for memory traces for sounds heard during nap time (via Newswise). The researchers tested children individually using a portable electroencephalogram (EEG) machine in a silent room at a university preschool. Once the children were asleep, three "nonsense words" were played to each child for a short span of time. Then, once the children were awake, they were again hooked up to the EEG machine and played the same words, mixed in with other words they had not heard previously. The children showed positive signs for recognizing these test words, indicating that they continued to process auditory information even when sleeping.

Thomas Andrillon, a research fellow at Monash University in Australia who worked on the Nature Human Behavior study, confirmed that people are more likely to wake up to relevant sounds. "It seems therefore that the sleeping brain remains somewhat vigilant," he told Vice. So even though it might seem like our ears turn off while sleeping, science tells us they're always on alert. Next time you think your sleeping partner or child in the room can't register what you're saying, think again.