Dear Prahlad,

After a quick catnap and a stretch, I went to visit my friend Marcos Frank, a scientist at Washington State University who studies animal sleep.

Even though animals sometimes look as if they are in the middle of a dream when their whiskers twitch and legs wiggle, we don’t really know if they are dreaming. They can’t tell humans about their dreams.

“The closest thing we can say is that animals exhibit some of the same sleep states that humans do,” Frank explains.

Dr. Universe cartoon cat character looking up to the skyWe cats have a reputation for sleeping a lot. But humans will actually spend about 25 years of their lifetime asleep.

Every night, about an hour and a half after you start to fall asleep, your eyeballs will start darting all around, under your closed eyelids. It reflects activity in your brain.

This stage is called REM sleep, as in “rapid eye movement,” Frank said. While your eyes are moving around, your body is paralyzed. Meanwhile, the brain is just as active as when you are awake.

Almost all mammals and birds go through this stage of REM sleep, too. Cold-blooded animals don’t appear to go through REM sleep, though.

But in humans, REM sleep is when dreaming usually begins. Because of this, some scientists think that if animals other than humans dream, it might happen in the REM stage.

As humans, it might be hard to imagine a sleeping brain that doesn’t dream. A lot of scientists have been wondering why humans dream at all. There’s actually a big debate among sleep scientists about dreaming, Frank explained.

Some think dreams are totally meaningless. Other researchers have found evidence that leads them to believe dreams might play an important role in how the brain works.

So, sometimes scientists will look at brains cells and brain activity in sleeping animals to find clues about dreaming.

In one study, scientists monitored the brain activity of singing birds. Then when the birds were asleep, scientists looked at the brain activity again.

It turned out that the brain activity was practically the same. It makes people wonder if the birds were dreaming about singing or could hear their own tune in their sleep. But we don’t know for sure.

Frank said there’s also evidence from animal studies that if you stop parts of the brain that keep sleeping animals from moving, they will behave in a way that makes them look like they are acting out a dream.

Whether or not they see a picture in their mind that goes along with their behavior, we still don’t know. As for your second question, if you think of all the different dreams you’ve had in your own life, it might help you get a sense of what dreams other animals might have—that is, if they dream at all.

Dr. Universe