Michael: Focus your eyes on this swinging watch. You're getting sleepy, very sleepy, and now when I snap my fingers you'll watch this whole video.

You might have see hypnotists make people fall asleep on command, quack like a duck, or even change personalities, like in the movie office space. And these performances can make hypnosis seem pretty questionable to the average skeptical person. So, is there really that kind of power in a soothing voice and a swinging watch?

Well it turns out that hypnosis isn't just a party trick. There is scientific evidence that being hypnotized is possible and might cause some real changes in your brain. Some psychologists even use it as a therapy to help patients with a bunch of different physical and mental conditions. So, hypnosis is probably real, just not in the exaggerated brainwashing way you might think.

Different meditation techniques and trance-like states have been documented for thousands of years, but what we consider to be modern hypnosis began in the 1700s, partially thanks to a physician named Franz Mesmer, which is where we got the word mesmerize. See, Mesmer had a theory about nature that he called Animal Magnetism, but he wasn't just talking about sex appeal. He thought there were invisible, magnetic fluids that flowed through living creatures and he claimed he could cure people of all kinds of illnesses by adjusting that flow.

Using dim lights, ethereal music, magnets, and flashy hand gestures, Mesmer induced a trance-like state in some of his clients and tried to balance this invisible fluid. Some of Mesmer's did get healthier after his treatments. So, when the scientific community put the theory of Animal Magnetism to the test, they found that a magnetic fluid with healing powers was, just, not a real thing. So, Mesmer and his research were discredited and many scientists didn't give the idea of therapeutic trance-like state a second thought, at least until the 1800s.

That's when surgeon James Braid began to study this potential therapy. He coined the word hypnosis to describe from the Greek word "Hypnos" because he thought that trance-like state was similar to sleep. Nowadays, clinical psychologists think that hypnosis only seems like drowsiness when it's actually a focused psychological state, kind of similar to meditation.

And unlike the flashy hypnotism you might see on TV, clinical hypnosis is pretty simple. It's all about focus, so hypnosis usually takes place in a dimly lit, quiet room. Sometimes, there is gentle music playing, but the goal is to remove all distractions. The hypnotist speaks softly, encourages the client to focus their attention on something, like maybe a dangling pocket watch, and walks them through relaxation exercise.

Eventually, they'll reach a state of Focused Relaxation, which just means they're calm, focused, and more open to suggestion. That way hypnotists can guide their clients through different visualizations or instructions depending on the goals of the hypnotherapy. Pretty simple, right?

Clinical psychologists agree that this relaxed and focused trance is the goal of hypnosis, but there are two main theories about what being hypnotized actually means psychologically. The altered state theory says that hypnosis actually leads to a distinct state of consciousness. Kind of like sleep, hypnosis might be a distinct state in the brain where your mental processes work differently and you're not necessarily aware of what's happening as if you were awake. On the flip side, non-state theory says that hypnosis is more like role play. Instead of being a distinct state, hypnosis might be a combination of intense focus and certain expectations about what it means to be hypnotized. Basically, you're still aware and playing along.

So right now researchers need more evidence to figure out what being hypnotized means in a psychological sense. But they have found that different people are more or less easily hypnotized.

Hypnosis is a voluntary process. So people have to be willing to listen to a hypnotist, focus and relax. But researchers estimate that around 10 to 15% of people are highly hypnotizable, meaning they slip more easily into a hypnotic state during a session. Another 20% or so are pretty resistant to hypnosis. And the rest of us fall somewhere between.

It's not exactly clear what makes someone highly hypnotizable or not, but one study found evidence that it might have to do with slight variations in brain anatomy. These researchers used magnetic resonance imaging or MRI and found that the subjects who were more easily hypnotized had a significantly larger rostrum than those who weren't. The rostrum is the region in the brain involved in attention.

Other scientists wanted to look at the brainwave patterns of hypnotized people. Basically, your brain depends on electrochemical energy to work because that's how your neurons communicate with each other. Using an electroencephalogram or EEG, researchers can monitor the electrical activity of your brain and see different patterns of brainwaves. In this study, the researchers found that hypnosis, especially in highly hypnotizable people, leads to an increase in theta waves, which are linked to attention and visualization. Like when you're doing mental math or daydreaming.

So both MRIs and EEGs seem to show that hypnosis can affect how our brains pay attention to things. which supports the idea that it is a state of focused relaxation. But how does that focused relaxation let hypnotists make suggestions and slightly influence what their clients think or do?

Well, it has to do with a concept called top-down processing. Our brains receive a lot of sensory information from the world around us. But we do a lot of processing and interpretation to figure out what's going on. The idea of top-down processing says that what you expect from memories and assumptions, the top level of information, can have a big impact on what you perceive with your senses, the bottom level of information.

Cognitive scientists have known this for a long time. And there are a lot of different experiments that show this effect. For example, a group of researchers had people drink wine that they thought was expensive and wine that they thought was cheap. They were actually the same wine, but the people said they enjoyed the expensive one more probably because they expected it to taste better. Not only that, but a pleasure processing part of their brains became more active when they drank the "expensive" wine as well.

Top-down processing also explains the placebo effect. If a doctor gives you a pill and says it'll make you feel better, you're probably going to say that it does, even if the pill was actually just made of sugar. Basically, this means that because a hypnotized person is more open to suggestions, their expectations can be tweaked, which can also change the way they perceive the world. And there's scientific evidence that hypnosis can affect perception like this.

Take the Stroop test, where you look a bunch of words describing colors like red, green and blue. But instead of reading the printed word, you have to say the color of ink the word is printed in. So if the word 'Yellow' is printed in blue ink, for example, you have to say "blue". It's pretty hard to do because of the conflict in the task. Your brain is processing the word and the color of the word at the same time.

So, a team of neuroscientists decided to use the Stroop test to see if hypnosis could affect how people perceive the words and their colors using a functional MRI scanner to monitor their brain activity. The researchers used relaxation techniques that hypnotize a mix of people who are highly hypnotizable, and less hypnotizable. Then the subjects were given a very specific suggestion. The words they would see in the fMRI scanner were gibberish, and they had to identify the color shown as quickly as possible.

A couple of days after the hypnosis session, the subjects took the Stroop test while having their brain scanned. And highly-hypnotizable people, who were probably more receptive to the suggestion, were faster and more accurate at picking the color of the words.

Even more amazingly, there were measurable differences in their brain activity. Specifically, a brain region responsible for decoding written words didn't become activated. So their brains didn't seem to be recognizing the words as words. At the same time, their brains didn't seem to register any conflict in the task, Unlike the brains of participants who were resistant to hypnosis. So it seems like hypnotic suggestion did change the subject's expectations so they perceived gibberish instead of words and could focus on the colors.

A different study by neuroscientists even found that hypnosis could block memories. The subjects watched a 45 minute film and came back a week later to be hypnotized. They were given a suggestion to forget the film when they heard a certain cue, and could have their memory restored with another cue.

Then the participants entered an fMRI scanner, and were given the forgetting cue. After that, they were given a test and couldn't remember the details of the movie even though they could remember details of the room they watched it in. Plus, certain memory related regions of their brains weren't as active as those of a control group, who hadn't been hypnotized. So, like you can theoretically be hypnotized to forget "The Empire Strikes Back" so you could experience the reveal of Luke Skywalker's father over and over again.

This phenomenon is known as post-hypnotic amnesia. and is actually used for models researching functional amnesia, like the kind that can be caused by traumatic brain injury. So even though some hypnotists use it as a party trick, some scientists are finding hypnosis to be a useful tool for medicine and psychology.

Some surgeons have used hypnosis before operations and medical treatments to reduce pain, anxiety and help with faster recovery. Hypnosis has even been used during child birth to reduce anxiety and pain. And hypnotherapy is sometimes used in combination with other behavioral therapy techniques for a bunch of conditions, from quitting smoking to mental illnesses like depression or PTSD.

At the same time, hypnosis isn't a cure-all. And hypnotic suggestions won't help everyone. So, is hypnosis real? Probably! But even psychologists aren't exactly sure about what being hypnotized means. Some think it's a distinct state of consciousness, while others think that being hypnotized is more about concentration and expectations. Mostly, hypnosis just highlights how powerful our brains are. If you don't want to relax and be put to sleep, you won't be. But you could possibly change your perception of the world to reduce physical pain, or even, force yourself to forget.

Thanks for watching this episode of SciShow and we hope you won't forget what you learned here today. If you want to learn more about psychology and the human brain, watch for our new channel coming out in the spring, SciShow Psychology, which was chosen by our patrons on Patreon. If you want to help us make videos and channels like this, you can go to patreon.com/scishow and don't forget to go to youtube.com/scishow and subscribe.