A team of researchers from New York University Neuroscience Institute recorded what they believe to be nightmares in the brains of rats while they slept.

The study, published in Nature Neuroscience, contends that when rats experience a frightening episode during the day while awake, the fear centers in their brains reactivate as they sleep.

To conduct the experiment, researchers set up a maze for rats to navigate through, and then blew a puff of air in the face of the rats at a specific spot within the maze – causing a frightening and unpleasant, but ultimately harmless experience for the rats.

After a few repetitive air puffs, the rats learned to be weary of the specific spot in the maze. According to the researchers, the rats would slow down prior to reaching to location, and then run speedily away in an attempt to avoid the air puff.

Rats store mental maps of the surroundings they encounter throughout the day in the hippocampi region of their brain. And similar to humans, structures called amygdalas, which are located near the hippocampi act as the “fear center” of the rats’ brains, and become active when the animals get scared.

The team observed the hippocampi becoming active as the rats learned to maneuver through the maze, and they were even able to follow the sequence of neurons that fired as a specific rat progressed through the maze.

But they also found that the amygdalas lit up when the rats were suddenly hit with the puff of air.

The rats’ brain activity continued to be analyzed as the animals slept. The researchers saw the same sequence of neurons they observed during the experiment also firing off as the rats slept, suggesting the rats were reliving the maze experience in their dreams. The amygdalas also lit up again, at the same point in the sequence where the rats were blasted with air in real life. These observations suggest that rats’ experiences during the day can come back to haunt them as nightmares.

The team admits in the study that they cannot definitively know what the rats were experiencing as they slept, but the findings do offer the opportunity for further research with humans, which could provide a much better understanding of the processes involved in human nightmares and even memory storage.