Last week, just as I was drifting off to sleep, my dog Rowdy made a weird noise. He was almost barking, but not quite. It startled me awake and, adrenaline slightly pumping, I was more alert when he then did it a second time. It was a weird noise, something like "berf." Like he was trying to bark without opening his mouth. I realized that he wasn't dying, nor had he heard an intruder downstairs. He was barking in his sleep.

Any of you who have pets, dogs especially, have probably noticed something like this. Dogs pretty regularly start twitching their legs while they sleep, or even moving them as if they're running. Our reaction is always "Aww, he's dreaming!" Well, that was my reaction the night of the berfs. But it got me wondering: do we really know if dogs dream? And how much do we know about it if they do?

Dreams are, of course, those weird mental scenarios that happen to us while we're asleep. You know, when you get together at a donut shop with your dead uncle and his dragon-car to watch Ghostbusters, starring Patrick Stewart as Sam Spade. And none of it seems even a little out of place until you wake up and think back on it.

We still don't have a complete picture of what makes dreams occur, or what purpose they serve, but we sure do know a lot more than when Sigmund Freud made a bunch of random stuff up a little over a hundred years ago. For example, we know that dreams most frequently occur in REM sleep. That stands for "rapid eye movement."

REM is a part of your sleep cycle that occurs multiple times throughout the night and involves fast brainwaves (sometimes there's even more brain activity than when you're awake) and, well, rapid eye movements. If you watch a person who's asleep you can actually see their eyes moving under their eyelids when they're in REM.

REM also involves the near complete paralysis of the voluntary nervous system, called "REM atonia." Well, normally it does, anyway. This is so people don't go around acting out their dreams. Some people have REM behavior disorder, which prevents this rather frequently, but anyone who has shared a bed knows that it occasionally happens to everyone. My wife punched me once, dead asleep.

Weirdly, sleepwalking doesn't appear to be related to this, since it happens during deep sleep (much slower brainwaves than REM), and, while dreams do occur in deep sleep, it's not as frequently.

We also know that there are different types of dreams. There are normal bizarre dreams, and then there are lucid dreams, when the dreamer becomes aware that he or she is in a dream. Some lucid dreamers report that they can actually take control of the dream when that happens. Then there are nightmares, distinct from the typical weirdness of dreams due to the immense amount of terror or misery they produce.

Then there's my personal least favorite, the hypnopompic hallucination. This actually happened to me once in college: I woke up, completely unable to move. Paralyzed from the neck down. I could hear the Beach Boys coming from my roommate's room. I knew for a fact he had no Beach Boys music on his computer. He was also visiting his family for the weekend. And yet I knew it, I could feel it, that someone was in his room listening to the Beach Boys. I was deathly afraid that they'd come for me next. I stayed that way for almost 15 minutes, watching the time tick by on my Garfield clock.

Then, suddenly and without warning, I snapped out of it. I could move. The sound and the sense of presence disappeared. It had all been a hypnopompic hallucination. It wasn't the first and it wasn't the last.

Basically what had happened was that I had awakened from REM but my entire brain hadn't gotten the message. I was still dealing with REM atonia, so I couldn't move, and part of my brain was still in dreaming mode, creating perceptions of things that weren't really there. Chances are this kind of freaky waking dream will happen to you at least once in your life. Just remember: no matter how much it seems like the aliens are really there with their terrible probes, it's just a hypnopompic hallucination. Probably.

So dreams we know about. We know that other people dream because they tell us they dream and we have no reason to doubt them. After all, we dream, too. Unless you want to assume that everyone else is a liar and just pretending to make you feel better about your weird sleep stories, or that only you really exist and everyone else is a figment of your imagination, it makes perfect sense to go with the idea that all humans can dream. Or at least most; my best friend can't, and I believe him, because he also has aphantasia, so it makes sense.

So what about dogs? Or cats? Or birds? Is it a rational leap to assume that a dog twitching his paws in his sleep is dealing with a minor bout of REM behavior disorder? After all, he can't tell us when he wakes up "Hey, man, I was chasing this giant chocolate rabbit. It was rad." Part of the impetus for me to learn more about dreaming was the thought, in the back of my mind, that maybe we're just anthropomorphizing our pets when we assume they're dreaming. Maybe those twitches, the sleep berfing, are a completely different phenomenon. Without talking dogs, or the ability to get inside the dog's mind and understand its experience, how could we know?

Well, as it turns out, we have this thing called science. And science can give us a limited view inside the mind of, well, anything we can fit the electrodes onto. That's how we know that REM sleep is characterized by fast brainwaves, muscle atonia, and an excess of a neurotransmitter called acetylcholine, which itself may cause REM sleep if a number of other neurotransmitters are depleted.

We can study people in REM, wake them, get a dream report, and associate dreams with specific patterns in electrical and chemical activity in the brain. We have done that, and we have a pretty solid idea of what a dreaming brain looks like. And guess what? When you apply the same process to non-human animals you get results that look an awful lot like human dreaming. Different species display different amounts of REM sleep, but when they're there they are, as far as we can tell, actually dreaming. Dogs, cats, possums, even some birds and reptiles.

Now, we still don't have the technology to wire directly into a dog's head and see what its mind's eye (if indeed it has one) is showing it while it dreams. And until we do, we'll have to rely on studying the externally apparent phenomena of dreaming instead of the qualia of the experience itself. But that's a whole philosophical rabbit hole unto itself, and it's been one of the greatest questions of consciousness since there were people to wonder about it.

Dogs twitch and run and berf in their sleep. They experience REM in nearly the same way humans do. They seem, to all appearances, to dream just like us. In short even absent a superscience brain image scanner, we have lots of good reasons to believe that dogs dream and no real reasons to believe they don't.

Someday that may change, but that's the beauty of science. We're learning as we go, always getting just a little bit less wrong.

Man of Random Science: Do Dogs Dream?