Question: Are our nightmares based of a mix-up of what has really happened to us or what we have seen? And why cant we remember the dreams we had in the morning sometimes?

Alex Reid answered on 5 Nov 2018: last edited 8 Nov 2018 10:44 pm

Hi thanks for your questions, they are both great. The answers are complex so apologies if this a long answer!

To (try) and answer your first question: are nightmares a mix up of what has really happened to us or what we have seen?

Dreams (and by extension nightmares) are likely a byproduct of memory processing (known as memory consolidation) while you sleep. In other words, they may not have a direct ‘function’ like a heart or lung. If you think of heat coming off a car engine, the engine was not made to create heat, it was made to move the car! When your brain shuffles around memories in sleep sometimes this is expressed as dreams or nightmares in your mind. They may not always make much sense as a result, and could be your brain trying to make sense of fragmented memories which then produce some bizarre imagery.

There is a special form of memory consolidation that processes emotional memories that occurs during Rapid Eye Movement sleep, and this is sleep stage you also dream the most in. As such, nightmares may sometimes be the result of your brain processing negative or unpleasant information, after all, these kinds of memories might be really important to your wellbeing.

To answer your second question: why can’t we remember dreams that well?

We are still working on this and there are probably a few reasons. Firstly, parts of your brain responsible for learning and storing information while you are awake switch ‘modes’ during sleep, and interact more. This helps consolidate memory, a process (or series of processes) that helps prepare your memories for future use. This means at a biological level your brain is not so much on ‘receive’ but is more focused on memory processing and reprocessing rather than learning and remembering new information.

Secondly, some dreams may actually be super mundane and not very memorable. While dreams are often thought of as being typically wacky and bizarre this is definitely not always the case. If you wake people up at different points in the night, particularly during the deepest levels of sleep, their dreams are often really mundane and boring. It is only when you get more to the end of your sleep cycle (when you get more REM sleep) that things get bit more visual, interesting and potentially more memorable.

Thirdly, time might be a factor as you are usually asleep for many hours. Psychologists have long known you typically have better memory for things that have occurred more recently (known as the recency effect). As such when you wake up you are more likely to remember the last thing you were thinking (or dreaming) about rather than things you dreamed of hours earlier.

Lastly, and this is my speculation, but I have a hunch our brains want us to forget dreams. Dreams may be a by-product of memory processing when we sleep, and it is not in our interests to confuse the vivid hallucinations we have with reality. If our ancestors got mixed up about where they last saw a big sabre tooth tiger because of a dream they might quickly become dinner! As such our brains may encourage (though hormones and varying brain activity) the quick forgetting of dreams to help us survive.