Question: Why do we dream while sleeping?

Stewart Martin-Haugh answered on 12 Nov 2018:

I’m a physicist, so not really my area. However, I believe it’s not understood well.

Let’s start with what we know: sleep is important to keep the brain functioning well. I think there are fairly good measurements for that, and it tallies with experience (if you’ve ever tried staying up all night, you’ll know what I mean).

There seem to be two main theories
1)Dreams have a specific purpose, e.g. processing events of the day, improving memories etc. This is backed up by things like the “Tetris effect”: play lots of something like Tetris and you will often end up playing in your dreams.

2)Dreams are just a side-effect of what’s happening in your brain: it’s just a side-effect of the changes your brain makes while storing memories etc. This is backed up by the similarity between dreams and the hallucinations people get from taking drugs.

The question is how can you tell these apart? In the last few years techniques like Magnetic Resonance Imaging (using similar techniques to those we use in physics to detect tiny particles) has shed a lot of light on how the brain works. Maybe in a few years we will have answers!