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Why should we sleep?

Updated on September 29, 2009

However one may try, it is hard to do away with sleep. Sleep is essential and moreover sleeping the right amounts is even more important.

Yawning indicates sleepiness and you being not that awake anymore. Your reaction time starts to stretch after being 18 hours without sleep. Beyond 20 hours you would take longer to respond sometimes half a second more than if you had slept and this time keeps moving up. Being sleep deprived for more than 20 hours is equivalent to drunk driving with an alcohol level of 0.08, which is high enough to be classified as driving under influence.

Yawning. Image Source:
Yawning. Image Source:

David Dinges, a sleep expert at the University of Pennsylvania, School of Medicine says, “By the second night, oh, my goodness, it’s extremely dramatic, beyond double what it was the first night. You fall massively off the cliff.”

The reason to sleep is still not precisely understood as to why we eat and why we breathe. Investigations are on by scientists though. Investigations have given them data to make some reasonable proposals on the need and exact benefits of sleep.

Mind refreshment seems the closest as to reasons of how sleep benefits us. Muscles need but just intermittent periods of relaxation and researchers have not found anything vital that sleep restores and hence body refreshment is not the best of reasons for sleeping. The brain is the one that is definitely benefited but only theories exist on how it’s benefited. The first being that sleep allows for review and consolidation of information streams gathered while awake. The next theory being sleep allows the brain to stock up fuel and flush out waste. Another theory is that sleep in some mysterious way aids mastering various motor skills, as to play the violin and driving.

EEG in action. Image Source:
EEG in action. Image Source:

Brain imaging and neurological mapping techniques are helping scientists with pictures of the brain while asleep and hence giving precise observations down to individual neurons. Dr. Giulio Tononi, a neurobiologist and psychiatrist at the University of Wisconsin at Madison says, “Suddenly we have hypotheses that could explain lots of things. Whether they’re right is a different story. But I feel different from a few years ago, when the thinking was, ‘Who knows? Sleep could be anything.’”

Scientists have learnt that most mammals, dolphins and whales being exceptions, cycle between two distinct phases of sleep, REM sleep and non-REM sleep. Humans usually take about 90 minutes to complete a full cycle of REM and non-REM sleep. REM sleep cycles increase as dawn approaches or by the time of awakening after having completed required amounts of uninterrupted sleep.

Sleeper awakened during REM sleep mentions of them being dreaming. Dreams are not experienced during non-REM sleep. The purpose of dreaming is still a mystery with scientists not being able to give any valid reasons as to why we dream and the purpose. It is believed though that dreams are random recycling of bits and pieces of previous day’s events.

Electroencephalogram (EEG), electromyogram (EMG), and electrooculogram (EOG) show activity of the brain, muscles, and eyes during three different states: wakefulness, REM sleep, and slow-wave sleep (SWS). Image Source:
Electroencephalogram (EEG), electromyogram (EMG), and electrooculogram (EOG) show activity of the brain, muscles, and eyes during three different states: wakefulness, REM sleep, and slow-wave sleep (SWS). Image Source:

EEGs (Electroencephalograms) reveal four distinct stages of non-REM sleep as we progress from light to deep sleep. Stages 3 and 4 are characterized by slow waves or low-frequency electrical waves. Researchers have named it slow-wave sleep. The initial three hours of sleep are spent in slow-wave sleep by humans, children being champion slow-wave sleepers. With aging slow-wave sleep decreases, this being the reason why adults are awakened more often during the night.

Researchers though were focused on REM sleep has more than often run into blank walls. Initially the dreams and things made the researchers focus on REM sleep as it seemed more interesting. Research of association of REM sleep and memory foundered when an Israeli man with shrapnel in his brain and not experiencing any REM sleep had no trouble attending law school and handling of new situations.

With new tools came new ideas. In the mid-90’s sleep research were revived, reasons being a study by scientists at the Weizmann Institute in Rehovot, Israel and their suggestions that researchers were looking at the wrong kind of memory processing. Further, the technology to look at a sleeping brain had got better.

The Weizmann researchers found that the ability to recognize certain patterns on a computer screen was directly tied to the amount of REM sleep gotten. These skills depended on what was known as procedural memory, which plays a role in any task that requires repetition and practice. Remembering a fact, like the inventor of airplane is declarative memory, a capability that is not affected by REM sleep.

“We were basically naive about memory,” said Robert Stickgold, cognitive neuroscientist at Harvard Medical School. Things changed once scientists knew which memory to study. Stickgold and Matthew Walker at Boston’s Beth Israel Deaconess Medical Center investigated sleep’s effects on procedural memory for motor skills. They made right-handed test subjects type a sequence of numbers with their left hand over and over and as fast as they could. Their accuracy increased 60% to 70% no matter what time of day the task was learned and after six minutes of practice. On retesting the subjects who had learned the sequence in the morning 12 hours later, no significant improvement was noticed. But those who learned the sequence in the evening and were retested following a night’s sleep showed an extra 15% to 20% increase in speed and were 30% to 40% more accurate.

The greatest improvements appeared in those who spent most of the time in the second stage of non-REM sleep, surprisingly. Procedural tasks heavily dependent on visual or perceptual ability required periods of deeper sleep or both slow-wave and REM sleep. An hour of shut-eye at times made a difference and at other times a full night’s rest. Stickgold mentioned, “It’s probably going to turn out that different types of memory tasks need different kinds of sleep.”

Cognitive skills linked to sleep are still being pursued. Jan Born and his colleagues at the University of Lubeck in Germany published a study showing the reasons of emergence of solutions often when sleeping over a problem. The study involved asking 106 test subjects to transform a string of numbers into a different string of numbers, using a simple but tedious mathematical equation. Unknown to the test subjects a hidden trick existed which could cut down on their response time drastically. The probability of the test subjects catching up with the trick more than doubled from 23% to 59% after a good night’s sleep. Sleep is not absolutely necessary to gain insight into a problem but could help.

With advances in computers and electrodes neuroscientists have been able to zero in on a single nerve cell and record its firing. To identify changing patterns of neuronal firing while asleep has been the goal. Bruce McNaughton, a psychologist and physiologist at the University of Arizona in Tucson has been studying rats has said, “There are days when we can record up to 500 neurons, but that’s not typical.” Typical is to tap 50 to 100 neurons. A rodent’s brain has 125 million neurons, but to get started Bruce feels it’s enough.

Bruce has noticed that neurons that fire during the day, say, when a rat is learning to navigate a maze are reactivated while the rat experiences REM sleep. Bruce says that the brain is reviewing its recently stored data. He mentions that eventually the brain consolidates those patterns into permanent connections. He recalls what neuroscientists say, “Neurons that fire together, wire together.” He also adds that interestingly the pattern appears to happen not just during sleep but during restful states throughout the day as well.

Some insight into the accomplishments of slow-wave sleep has also been had with advancements in technology. Wisconsin’s Tononi and others had published in Nature a study which showed a specific part of the brain that had been busy learning a new skill while awake needed much more slow-wave sleep in order to improve performance.

The study involved 11 volunteers to play a video game that required them to reach objects on the screen with a mouse-controlled cursor. Unknown to the volunteers the game at times introduced a slight bias to the cursor’s motion, forcing them to adjust their movements. Half the group slept while another half didn’t. Among the sleepers, it was noticed that the region of the brain associated with learning to compensate for the bias while awake had the largest slow wave sleep during sleep. Tonoi mentions, “The bigger the slow waves were in that part of the brain, the better they performed the next day.”

As an explanation Tonoi speculates that instead of strengthening neural connections responsible for a given task, as appeared to happen during the day or in REM sleep, slow-wave sleep weakens the connections among all nerves. Tonoi says, “Normally the brain takes up 20% of the energy of the entire body” Most of this energy is used to sustain the connecting points, or synapses between neurons. More learning adds to greater numbers of synapses. “So by the end of the day, if you have synapses that are much stronger, the cost of running the brain is much higher,” Tonoi says.

So a neuroscientist knows that the number of new synapses in the brain would require more energy than the body could possibly supply. Hence some connections need to be weakened, and this best is guessed to happen during slow-wave sleep.

Though hypothetical the explanation may seem Tonoi seems to have the evidence to back it up. “In slow-wave activity, all the neurons fire for half a second,” he explains. “Then they’re totally silent for half a second.” That seems to be the way for the brain to lower the strength of the connections between its neurons. Connections becoming leaner and even the dropping out of the weaker ones are the consequences of intermittent firing, thus clearing the mind for the learning of something new in the morning.

So, sleep is a series of repeated cycles of pruning and strengthening of neural connections that enables us to learn new tricks without forgetting old ones. Again there are no answers why one needs to be unconscious for the pruning and strengthening to happen. “When you fall asleep, it’s like you’re leaving your house and the workmen come in to renovate,” suggests Terry Sejnowski, a computational neurobiologist at the Salk Institute of La Jolla, California. “You don’t want to live in the house while the construction’s going on because it’s a mess.”

Not everybody is convinced though. Robert Vertes, a neuroscientist says, “It may not sound exciting, but I think sleep is essentially for rest.” He thinks most scientists find it hard to believe that the brain needs to shut down for eight hours or so every night and have been overly interpreting their data. “We don’t know,” he says is the shortest answer to what the brain does during that time.


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