What exactly your brain does when you rest peacefully at night? Before the 1950s, most people believed that sleep is a passive activity during which the brain remains dormant. This myth was debunked later. In fact, our brains have an intense nightlife and remain hard at work while we cozily sleep. They’re constantly busy processing the happenings we experienced during the day and consolidate them in memory, while simultaneously keeping track of what’s going on around us, cleansing toxins, and readying us for the next day.
Researchers are continuously spending time trying to learn more about these nightlife activities of brain. As per Mark Wu, M.D., Ph.D., a sleep expert and neurologist at Johns Hopkins University, “Sleep is a period during which the brain is engaged in a number of activities necessary to life, which are closely linked to quality of life.”
The Brain’s Inner Workings
As per John Peever, director of the Systems Neurobiology Laboratory at the University of Toronto, and Brian J. Murray, director of the sleep laboratory at the Sunnybrook Health Sciences Center, the function of sleep has mystified scientists for thousands of years, but modern research is providing new clues about what it does for both the mind and body. Sleep serves to re-energize the body’s cells, clear waste from the brain, and support learning and memory. It even plays vital roles in regulating mood, appetite and libido.
Even with all the advancements in science, the brain’s inner workings are still largely a mystery. This mystery even magnifies when we’re asleep. While we sleep cozily, the brain never completely tune out the environment and is always making connections. Several studies have found different ways in which the brain processes information while we sleep comfortably. Further, these studies have led to new ways to enhance learning and treatments for some characteristics of neurological disorders.
As per neuroscientist, Dr. Maiken Nedergaard, our brains perform two different jobs. It seems they have daytime jobs. Later they ‘moonlight’ at a nighttime job. Moonlighting is working a nighttime job in addition to a day job. So, actually our brains work an extra job at night without additional pay for overtime.
During daytime, the brain cells work very hard at processing all the information about our surroundings. Whereas during sleep, they work very hard at removing all the waste that builds up when we’re awake during the day. This waste material includes poisons, or toxins, responsible for brain disorders such as Alzheimer’s disease. As per Dr. Nedergaard, these toxins end up in the liver. There, they’re broken down and then removed from the body.
Hearing During Sleep
A study by scientists at University of California, Los Angeles used sounds to explore how sleep blocks sensory signals from waking us by reaching our conscious awareness. The researchers found that when they played sounds, the individual neurons in the area of the brain responsible for early auditory processing responded when the subjects were asleep. However, the usual neural feedback signaling associated with conscious recognition was absent.
Their results suggested that the brain processes sensory information when you sleep, but your consciousness is not made aware of it. The lack of feedback signals from the consciousness lost during sleep is the reason that quiet or constant noises don’t wake people.
A 2019 study published in the ‘Human Nature Behavior Journal’ found that, during sleep our brain pays attention to the sounds around us. Not only that, the brain pays more attention to some sounds than to others.
The study was designed to mimic the ‘cocktail party problem’ where participants would hear a number of sounds, almost as if they were at a party. When you’re at a loud party, you have to select which voices to pay attention to, and which ones to ignore. For this sleep study, researchers focused on just two voices: one voice was saying sentences and phrases, while the other voice was speaking gibberish. As participants drifted off to sleep, they kept hearing these two voices played through headphones. Their brain activity was monitored using EEG, and the researchers saw that even in sleep, participants were paying more attention to the meaningful voice than the gibberish voice.
Relational memory is the ability to remember arbitrary associations between objects or events. These memories include things related by location, order, and context. As part of regular life, humans are constantly processing everything they feel, see, hear, smell, and taste, both day and night. However during sleep, memories we make during the day are consolidated and become more permanent. The story doesn’t end here. The brain does much more than just recording and consolidating what you’ve experienced during the day; it also makes new connections of related events during sleep process.
Maxim Bazhenov, a professor of medicine, and Timothy Tadros, a doctoral graduate from Bazhenov’s lab at University of California San Diego, wrote an article in which they described their theoretical modeling explaining processes that can create and strengthen relational memories during sleep.
The authors modeled interactions between two parts of the brain, the thalamus (a structure, nicknamed ‘the gateway to the consciousness,’ that processes sight, hearing, taste and touch signals before you’re consciously aware of them) and the cerebral cortex (where attention, perception and cognition occur) to test how associative memory formation occurs during sleep. In earlier models, researchers found a process called sleep replay, where neurons that are involved in previously learned tasks activate during sleep. This new model explored how associative memory arise in memory formation during sleep replay.
Using this model, the brain was shown A+B and B+C, where A and C are faces and B is a name associated with both faces. A, B and C were then consolidated into memory during sleep. However, the brain takes it a step further by activating all the neurons relating to A, which causes neurons related to B to be activated and, therefore, C neurons as well. Even though A+C was never directly associated, the brain has linked them. Understanding this process may help to improve relational memory, particularly in people with schizophrenia and autism spectrum disorder, since these and other disorders are known to cause problems with associative memory.
Motor Skill Improvement
All of us have heard the famous saying, “Practice Makes Perfect”. However, when it comes to enhancing motor skills, practice may not be the only important thing.
Researchers at Northwestern University carried out a study to investigate if ‘execution-based movements’ can be improved during sleep. They started by having participants associate specific sounds with electrical activity from specific arm movements by practicing these movements first with visual and auditory cues and then only with the auditory cues. The participants were then asked to nap, and sounds, including half the auditory cues, were played once they fell asleep.
By playing the sounds associated with the movements, the researchers were using targeted memory reactivation to activate the memories of the movement, while the participants slept. The researchers found that there was a marked improvement in how quickly and directly the participants responded to targeted memory reactivation from the cues they heard while they slept.
This finding indicates that brain plays through motor skills during sleep, which acts as additional repetition of the mental components of movements. This information could be used to help not only people trying to get a set of movements down, but also rehabilitation therapy patients with motor dysfunction due to neurological insult or injury.
Clearly, the brain is an amazing organ. While we sleep to restore our energy and have a clearer mind, the brain is still active and constantly analyzing what our senses tell it of our surroundings, making and replaying connections between things we have seen and experienced throughout the day. This not only allows us to remember what happened yesterday, but also prepare us for tomorrow.