The cause of transitions between sleep stages has confounded the medical field but a new study may help explain what triggers the shift between non-REM and REM sleep. The researchers studied mice and their transition into REM during sleep. The researchers found that just before mice shifted from non-REM to REM, there was an increase in dopamine levels. To further understand this, the researchers controlled the dopamine-producing nerve cells and while the mice were sleeping, forced them into REM. The next step for the study would be to understand if the same happens in humans and if so we will be closer to developing more effective and targeted sleep aids for people with sleep disorders.
https://www.sciencenews.org/article/dopamine-mice-rem-sleep-dream