Scientists at the Universities of Bern and Fribourg (Switzerland) may have put their finger on the old question of why we remember some dreams and not others. The research team identified for the first time the neurons of the nucleus papilio that are responsible for the rapid eye movements during sleep. Their research was published in the journal Nature Communications.
The rapid eye movement in REM sleep is present during a period of high dream activity. This phase of sleep is called REM because the muscle relaxation of the sleeper is associated with rapid eye movements. Although this sleep phase was discovered by French and American researchers back in the 1950s, the understanding of the usefulness of this strange phenomenon remains limited. According to the scientists, rapid eye movement is thought to accompany the work of storing information that occurs during REM sleep, and explains in part why we remember some information when we wake up.
Influencing eye movements during sleep
The nucleus papilio – a structure in the brain stem that is so called because it resembles the wings of a butterfly – was investigated by the team led by Franck Girard and Marco Celio at the University of Freiburg. Franck Girard explained his approach: “These neurons are connected to several nerve centers; in particular those responsible for eye movements and those involved in sleep control. We therefore asked ourselves the following question: Can the nucleus papilio play a role in controlling eye movements during sleep?
Following the publication of the hypothesis, the research team in Fribourg collaborated with Dr. Carolina Gutierrez Herrera from the Neurological Department of the University Hospital of Bern and Professor Antoine Adamantidis from the Biomedical Research Department of the University of Bern, who studied sleep in rats.
Variation in the intensity of rapid eye movements
Carolina Gutierrez Herrera discovered during her research that the nucleus papilio neurons are particularly active during REM sleep, which allowed researchers at the University of Bern to take a closer look at the loop around the papillary core neurons. Using optogenetic methods (combined optical and genetic techniques), the researchers have shown that their artificial activation causes rapid eye movements, especially in this sleep phase. They also found that the inhibition or elimination of the same neurons blocks the movement of the eyes.
The researchers are now focusing their attention on confirming the effects of activating nucleus papilio neurons during REM sleep in humans.
In their conclusion, the researchers say that identifying the nucleus papilio neurons responsible for REM sleep could soon help scientists to better understand the neural circuits involved in REM sleep. This discovery would also help to understand how these neurons undergo degenerative changes in diseases such as Parkinson’s disease.