Neuroscience of Dreams

Why do we dream?

Sleep itself may be a mystery, but so are the many strange occurrences that we experience while we sleep – the most well known of which is dreaming. We don't know why we dream, or if it even has an evolutionary benefit, but studies hint at potential reasons. 



One idea is that dreams help us process memories which have formed during the day, and convert them into more stable long-term memories. We know that sleep is vital for this process, but whether dreams help isn't clear. Interestingly, young babies spend a higher proportion of their sleep in REM sleep (the phase during which dreams are most likely to occur). As babies learn more rapidly than adults, could this mean they need to dream more to process the information? 

Another idea is that dreams help us deal with difficult emotions in a safe way. They may help remove emotions from painful memories so we can recall them without experiencing the emotions as strongly. They may even help prepare us for potential future emotional situations, by giving our brains a 'rehearsal'. But this theory is difficult to prove. 

One final idea is that dreams aren't 'for' anything at all – they are simply a byproduct of the other vital processes out brain carries out during the night. Will we ever be able to determine which of these theorise is correct, or will dreams remain a mystery? Only time will tell...

Babies not only spend more time sleeping, they also spend a higher proportion of their time in REMsleep than adults. 

Scientists believe that everyone dreams, but not everyone remembers these dreams when they wake. We don't know exactly why this is, although part of the reason may be that high recallers spend more time awake during the night, suggesting they are more likely to have woken up part way through a dream, which we know increases your chance of remembering it. This isn't enough to explain all the differences, however. 

You have the best chance of recalling a dream if asked about it within 5 minutes of waking – after this, much of the detail is lost. So maybe those who remember dreams make an effort to recall them during this window, and in doing so store them for later. If you want to recall more of your dreams, experts suggest keeping a dream journal, and writing down details in it as soon as you wake. There are also brain differences between low recall and high recall groups. For example, high recallers are more "responsive" to their name being called when awake, and show a greater brainwave change – although the difference doesn't occur when asleep, so it's not clear how it links to dream recall. One brain scanning study found high recallers have more activity in a part of the brain called the "temporo-parietal junction". The researchers believe this may allow the dreamer to focus more attention on external stimuli, meaning dreams are better embedded in the sleeper's memory.

Not everybody can remember their dreams. Can you catch yours?

Some people experience lucid dreaming – dreaming whilst aware that they are dreaming, and some even feel they are controlling the direction of their dreams. It is difficult to know for sure whether lucid dreaming is real sleep, but because it occurs during REM sleep, dreamers can use pre-arranged eye signals to communicate with researchers. We don't know how people are able to control their dreams, or whether or not this means they're "truly dreaming" or a daydream-like state of semi-wakefulness. The phenomenon warrants further study. 

In recent years, researchers using fMRI to scan brain activity during dreaming have developed a process that can map the images recalled by the dreamer to a 3-dimensional picture of the brain. Known as “dream decoding”, the process works by repeatedly waking a sleeper and asking what they remember, then pairing this with which bits of the brain light up in the scanner. After over 200 repeats, researchers have been able to use the tool to predict basic objects that appear in the dream, including men, words and books. The tool is currently 60-70% accurate, but could be improved with more data. Scientists are keen to explore how effective this tool could get and whether it could be applied to more complex imaging or decoding our intentions.