Dreams have always been a subject of intense fascination. From oddly fantastic flying dreams to the classic fleeing dream, from mundanely nonsensical dreams to inspirational dreams, dreams intrigue us, inspire, chill or soothe us. But do animals dream?

Many animal owners believe they do. Sleeping pets commonly display dream-like behavior, starting with twitching eyelids and facial tics that often progress to animated paws or legs moving in like motion. A choked whimper or growl might issue from the throat, all appearing to indicate the animal is dreaming. But if animals dream, what kind of dreams do they have, and what purpose do they serve?

Studies conducted in 2000 at the Massachusetts Institute of Technology (MIT), led Cambridge researchers to believe that not only do animals dream, but their dreams can be highly complex involving long sequences of replayed waking events. Results, published in the 2001 January 25 issue of the Neuron journal, suggested that rats trained to run a track dreamed about their experiences.

In the MIT studies, rats ran a circular maze for a reward while researchers mapped the animals’ brain activity using electrodes. Scientists found that neurons fired in a specific pattern, depending on the rat’s position along the maze, and whether it was moving or standing still. Scientists also noted neural activity took place in the hippocampus, the area associated with memory.

While the animals slept, electrodes continued to record brain activity. Like humans, rats experience various stages of sleep, moving from slow-wave sleep to rapid eye movement or REM sleep (where humans do their dreaming).

MIT researchers studied over 40 REM recordings from the rats. When the animals slept, about half of them repeated the signature neural pattern seen during the waking maze exercise. The correlation was so precise scientists could pinpoint where the dreaming rat was in the maze, and whether it was sitting or running. They concluded that reactivating memories could be a mechanism for instilling the experience into long-term memory, making a good case for at least one reason why animals dream. A rat that remembered how to navigate the maze by “practicing in its sleep” was more assured of food.

Prior to these studies scientists assumed only a relative few species of animals such as dolphins and primates were capable of recalling complex memories built around multiple, sequential events. MIT researchers now conclude it seems likely that most animals dream and are capable of more complex thought processes than scientists previously thought.

While it’s very interesting that animals dream there are practical applications for humans. By studying how memory is formed and which experiences are relived and retained, researchers hope to find help for victims of memory disorders like amnesia and diseases such as Alzheimer’s.