Every animal you can think of -- mammals, birds, reptiles, fish, amphibians -- has a brain. But the human brain is unique. Although it's not the largest, it gives us the power to speak, imagine and problem solve. It is truly an amazing organ.

The brain performs an incredible number of tasks including the following:

It controls body temperature, blood pressure, heart rate and breathing.
It accepts a flood of information about the world around you from your various senses (seeing, hearing, smelling, tasting and touching).
It handles your physical movement when walking, talking, standing or sitting.
It lets you think, dream, reason and experience emotions.

All of these tasks are coordinated, controlled and regulated by an organ that is about the size of a small head of cauliflower.
Your brain, spinal cord and peripheral nerves make up a complex, integrated information-processing and control system known as your central nervous system. In tandem, they regulate all the conscious and unconscious facets of your life. The scientific study of the brain and nervous system is called neuroscience or neurobiology. Because the field of neuroscience is so vast -- and the brain and nervous system are so complex -- this article will start with the basics and give you an overview of this complicated organ.
We'll examine the structures of the brain and how each section controls our daily functions, including motor control, visual processing, auditory processing, sensation, learning, memory and emotions.

If you try to make a list of the things you did in the last 15 years, it would probably look like this: three years in junior-high, 20 months with your boyfriend, a year of study in Italy. Forgetting anything? As a matter of fact, you are leaving out the one thing that you spent the most time doing. Sleep. This major time consumer took about five years from the past 15.

While adults spend about one third of their time sleeping, babies and toddlers sleep away half of their early childhood. It cannot be the terrible waste of time that it seems. Or can it be? Embarrassingly, scientists still cannot persuasively point out the biological function of sleep. Sex, eating, and sleeping constitute the triad of basic impulses of human beings. Yet, while the functions of the first two have been obvious for millennia, it is not clear why we crave to spend a third of our life in bed.

Over the past decade, new findings that may lead to the resolution of this conundrum have been accumulating. Many scientists believe that in a few years we will understand not just why we sleep, but also what biochemical mechanisms underlie this odd activity.


Koalas spend up to 20 hours a day sleeping.

The first few hints for the function of sleep came from observations on animals. All mammals sleep, as do birds and even bees. One theory suggests that sleep is a simple protection mechanism, a way to keep animals quiet and still, so that they attract less attention, and thus are less noticeable to predators. This stillness is particularly important when the animal is most vulnerable, which for many animals, is during the dark of night. But comparing sleep patterns of different species suggests that this may be too simplistic an explanation. Opossum, for example, sleep up to 20 hours a day. Giraffes, on the other hand, spend no more than 20 minutes a day sleeping, and don't even bother to recline their cumbersome bodies. Dolphins and whales also spend a very short time sleeping, and continue to swim even as they catch their Zs. Some scientists even claim that dolphins let only half of their brain sleep at a time. This diversity of sleeping patterns implies that sleep is more than just a way of keeping animals quiet. There must be another explanation.

Clearly, sleep is an opportunity to rest. Hence, many theorists have hypothesized that the main purpose of sleep is to enable the muscles and the brain to recuperate after a busy day. But measuring the electric activity of the brain unveils the shortcomings of this theory: A sleeping brain is far from dormant.

When measured using EEG, the electric activity of a brain when asleep is no less hectic than it is when awake. There is a difference, though, between two different phases of sleep. Right after falling asleep, the brain demonstrates slow EEG activity. This stage is called slow wave sleep (SWS). However, after a while, the brain goes into the turmoil of the second stage, which due to its similarity to the brain activity of attentive wakefulness, is known as paradoxical sleep. In this stage, the EEG reveals very fast activity. At the same time, the eyes move rapidly, giving this stage its other famous name -- REM (Rapid Eye Movement) sleep. REM sleep is also the time during which we dream.

A number of fascinating experiments suggest that this jittery second stage is the daily session of memory maintenance and that during this time, the brain reviews and sorts the knowledge that it has encountered during the day. Some of it is discarded and some of it is stored in the appropriate context. According to this theory, sleep is required for learning and memory.

In a few experiments, rats were trained to find their way through a maze while electrodes were recording the activity of their brain. When the rats fell asleep, the brain started to behave oddly. In light of difficulties of getting a clear verbal description from the rats regarding their dreams, we can rely only on the pattern of their brain activity. The rats' brain activity during sleep was highly similar to the activity during the training. The brain seemed to reconstruct the experience of the day. In their dreams, the rats were again chasing the cheese through the maze.

Other experiments supplied more direct evidence that sleep is crucial for learning. Human subjects were trained to identify letters that appeared for a blink of an eye on a computer screen. Then, half of the subjects were sent home to sleep, while the other half were deprived of sleep for the entire night, and only then went home to rest. Two days later when all the subjects were already rested and refreshed, the scientists checked their ability to read the flashing letters. None of the participants were tired, and yet the people who went to sleep right after the training performed much better than the ones who went to sleep a day later. This suggests that the night sleep immediately after the activity was crucial for gaining the most from the training session. Without it, the training was much less effective.

The fact that during their formative years of childhood and adolescence, people sleep much more than during their adulthood, also supports the view that sleeping plays a role in learning. Yet, some scientists claim that this evidence is still weak, and more importantly, that other experiments yield contradicting results. Therefore, they argue, declaring that the mystery of sleep is resolved, and that the main function of sleep is to enhance learning, would be premature.

Only future research can decide this debate. In the mean time, if you are planning to pull an all-nighter before a big test, you may want to reconsider. When you go to sleep your brain may still be studying. Perhaps this night session is as crucial for your success as the learning you do when you are awake.