Some people can always recall their dreams as vividly as their daytime memories, while many insist that they don't dream at all (or at least can’t remember them). It turns out, this difference could perhaps be explained by just two genes that regulate it.

Unfortunately, this discovery was made by scientists removing the ability to dream from a mouse's brain. 

New research – carried out on mice, not humans – from the RIKEN Center for Biosystems Dynamics Research in Japan has discovered a pair of genes that regulate the amount of REM (rapid eye movement) sleep, the phase of sleep associated with vivid dreaming, and non-REM sleep an animal experiences. As reported in the journal Cell Reports, the study could help to shed light on the nature of REM sleep and even question the purpose of dreaming.

When you hit the hay at night, your body drifts in and out of different stages of REM and non-REM sleep. Not only is REM sleep linked to periods of dreaming, we also tend to remember our dreams better if we are awoken during a phase of REM sleep. More REM sleep, therefore, tends to mean a higher chance of having and remembering dreams.

When we enter a phase of REM sleep, the brain is flooded with a neurotransmitter known as acetylcholine. The underlying neural network is unbelievably complex, however, scientists do know that acetylcholine appears to play a strong role in the regulation of REM sleep. For this new study, researchers managed to pinpoint two genes, Chrm1 and Chrm3, that appear to encode for numerous acetylcholine receptors.

To find out whether these genes really played a role in our dream phase of sleep, they used genetic tools to modify the genes of mice. They discovered that removing Chrm1 reduces and fragments REM sleep, while knocking out Chrm3 reduced the length of non-REM sleep “to an almost undetectable level.” When both were knocked out, the mice experienced barely any REM sleep – they literally stripped the mice of their dreams.

"The discovery that Chrm1 and Chrm3 play a key role in REM sleep opens the way to studying its underlying cellular and molecular mechanisms and will eventually allow us to define the state of REM sleep, which has been paradoxical and mysterious since its original report," lead author Professor Hiroki Ueda said in a statement.

It’s thought that REM sleep helps our brains to manage memories, emotions, and learning. However, the "dreamless" mice did not appear to be affected at all by their lack of REM sleep. This might not necessarily be the case with humans too, but the researchers argue it could show how dreaming doesn’t actually serve a functional purpose; it’s simply a by-product of brain activity during REM sleep.