Magazine 杂志：What are dreams for?

The quick answer is that nobody knows. The long answer is that are lots of different theories. So, if you’re interested, read on!

Some theories of the purpose of dreams

Freud believed that we dream so that we can release the deep, secret desires that we are not allowed to express in real life because of the rules of polite society. Most people know about Freudian dream analysis – a dream about a train going into a tunnel is a dream about sexual intercourse. But couldn’t it just be a dream about travelling on a train?

Another theory is that dreams allow us to solve problems that we can’t solve in real life. We go to sleep with a problem and wake up with the answer. This may be more of a way to ‘use’ our dreams than a ‘purpose’ of dreaming. If you believe that your dreams are important then analysing them may help you to focus your mind on the problem and help you to find the solution.

The modern image is that dreams are the brain’s way of cleaning up the computer’s hard disk, organizing the events of the day into folders and deleting the rubbish that it doesn’t want to keep. But we all know that very little of what we dream every night is concerned with what happened to us that day.

Another idea is that dreams are the brain’s way of practising the behaviour that we need to survive. So we dream about being chased by a monster because one day it might happen! It’s a bit like a pianist practising her scales every day even though she doesn’t need to use them at that moment.

Others believe that dreaming is the brain’s way of exercising the pathways between the brain cells. This may be an important element in why we sleep rather than why we dream. We die if we don’t sleep but we can live without dreaming. Some patients with brain injuries lose the ability to dream but don’t seem to suffer any ill-effects.

REM and dreaming

Scientists used to think that dreaming only happened during Rapid Eye Movement sleep (REM). REM sleep is essential for all mammals. We all become irritable and depressed without it. If we don’t have enough REM one night, we will compensate by having more the next. REM is generated by the brainstem – the oldest and most primitive part of the brain. So scientists used to believe that dreaming was also caused by activity in the brainstem. We now know that dreaming can happen at any time during sleep. The only difference seems to be that it’s easier to remember dreams that happen during REM.

Babies have a lot more REM activity than adults, but research shows that they dream less. The same may be true of animals. We know that they have REM activity but that doesn’t mean they dream.

It also seems that dreaming is a skill that develops as you get older, like language for example. Young children’s dreams are very different from older children’s or adult’s dreams.

New research

Modern technology has allowed scientists to map the parts of the brain that are active when we dream. The primitive brainstem is very active, but so are other important areas at the front of the brain. These are the frontal lobes that control emotion, memory, and experiences that come through the senses like hearing and vision. If these areas are injured, the person stops dreaming. On the other hand, the areas that control rational, logical thought are not active at all. This could explain why dreams are so strange. They have no logical sequence or time, which makes them very difficult to explain to other people when we wake up. Dreams combine recent events with long past events and our emotions while we are dreaming are often very strong.

Psychologists have also done studies on people who kept dream diaries for long periods of time (up to fifty years in some cases) and have found that what we dream is very much connected with how we think and behave when we are awake. So an extrovert, adventurous person will have extrovert, adventurous dreams. A shy person will be a shy person in her dreams. People who are important to us will often be in our dreams and so will things that worry us or make us happy.

So what’s the conclusion?

Well, nobody really knows. But scientists are now suggesting that dreams have absolutely no purpose at all. When we are awake we are ‘thinking’ all the time. Some of this thinking is useful and has a purpose. But we often just ‘think’ about nothing in particular while we’re waiting for the bus or walking to work. And that’s what the brain is doing when we are asleep - just thinking. Sometimes it’s interesting and sometimes it’s boring.

Doing the research for this article has made me more interested in my dreams rather than less. I might even start a dream diary! But nothing that I’ve read explains why I sometimes have an embarrassing dream about finding myself standing completely naked at a bus stop. Fortunately, this has never happened to me in real life, and it isn’t something that I think about when I’m awake. I’m told that it’s an example of a ‘universal dream’ – a dream that is common to people all over the world. Dreaming about flying is another example. So what’s the explanation? We can’t all be ‘just thinking’ about the same thing, can we?