Question: why do we dream and why do we sometimes forget our dreams and what do dreams mean ?

Alex Reid answered on 8 Nov 2018: last edited 8 Nov 2018 6:17 pm

This is a great set of questions and it really covers a lot of areas of research so forgive me for the long answer(s). First: why do we dream? Our best understanding of dreams at the moment is that they are a by-product of other processes going on during sleep. Specifically, during sleep your brain engages in a lot of what we call ‘memory consolidation’, this is a process (or series of processes) help prepare your memories for future use. During this, memory fragments get moved and shuffled around in your brain as different brain regions ‘talk’ to each other. Dreams are probably when your brain ‘overhears’ this conversation. It is your mind trying to make sense of this jumble of information. As such, dreams may have no direct ‘function’, like a heart or lung, and instead are a bit more like the heat that comes off a car engine. A car engine was not made to make heat, it was made to move the car!, nevertheless we still get heat.

Why do we sometimes forget dreams? This actually requires a bit of a longer answer, and I answered this somewhere else, so I am going to edit what I said and add it here. There is probably more than one reason why dreams are really forgetful and we are still trying to figure out why but it is probably for more than one reason. Firstly, because of the previously mentioned memory consolidation 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 of a type of sleep called Rapid Eye Movement 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.
Some of what I said helps answer your last question: what do dreams mean? Well they might not mean anything in and of themselves, they are a byproduct after all. However this does not mean they might not be personally meaningful, and they can often reveal things that you might not have directly thought about. They are often used, with some success, in discussions for some therapies to help people with ongoing issues. They are also inherently creative, and have inspired a lot of excellent art, in particular the surrealist movement (check out here to see some paintings of dreams: https://en.wikipedia.org/wiki/Surrealism).