Nightmares may not be an experience exclusive to humans alone. New research finds that rats might have scary dreams when they fall asleep too.
The study, published in Nature Neuroscience, was performed by scientists from New York University, who did an experiment that demonstrated that when rats go through frightening stages, the panic reaction they feel is reactivated during sleep. An experience perhaps similar to what some of us face when we decide to watch a scary film before bed.

To carry out the research, the scientists put the rats in a maze. At a certain spot, the team aimed a puff of air from a keyboard cleaner at the rats to startle them. The rats, of course, learned to fear this spot.

“They slow down before the location of the air puff, then run superfast away from it,” said study author Gabrielle Girardeau to New Scientist.
The team then recorderd the activity of the rats’ hippocampi and amygdalas during the maze experiment and as they slept. The amygdalas are two almond-shaped structures in the brain linked to fear, as well as decision-making and memory. When the rats nodded off, the same pattern of acitvity in their amygdalas activated, as the fearful recollection of the maze was played out.

Buzsáki commented on whether we could completely tell if the rats were reliving their emotions in the maze during their dream: “We can’t ask them.” However, “it has been fairly well documented that trauma leads to bad dreams.”

Other scientists commented on the research. James Bisby of University College London felt it may not necessarily be a nightmare the rats are having, but something more similar to a “memory strengthening process” that enables the rats to retrieve the memory later beause it’s stabilized.

Original paper

Reactivations of emotional memory in the hippocampus-amygdala system during sleep. Gabrielle Girardeau, Ingrid Inema & György Buzsáki. Nature Neuroscience, 2017. [PDF] [Link]