Apparently people normally dream for about 2 hours every night, and there are several theories about why we dream. Some people think it is a mechanism for converting things in your short-term memory to your long-term memory, or a way of removing useless information from your memory. It is true that you often dream about things which you have seen or experiences that day. Nobody is entirely sure where dreams originate, but people with damage to the parietal lobe don’t seem to dream
It’s a great question and the simple answer is I don’t have a scooby doo! What I do find interesting about dreams is often their vividness or how clear it is. When we imagine doing something, it can evoke a similar physiological response to what would happen if we were to actually do it (something psychologists call functional equivalence). So if you were to imagine very clearly your favourite food, the colour and the look of it on the plate…the smell of it as you lower your head to breathe in the aroma… and the texture as you lift it up and place it between your lips.., its possible that for some of you, you may find yourself starting to salivate? That may not answer necessarily the question of how they are caused, but it could help in part to answer the question of how dreams are created, in a descriptive sense, if the areas of the brain involved in imagination, were similar to those areas involved in dreaming.