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Public speaking is terrifying for a lot of people, and it was especially stressful for people like Isaac Newton and England's King George VI— because at some point, they each had a stutter. The exact symptoms vary, but someone who stutters has trouble speaking in fluid, connected sentences.

Which is not fun to deal with if, say, you are a king who is expected to give speeches all the time. Like many things in psychology, we're still trying to figure out exactly what causes stuttering in the first place. But, despite what a lot of people think, stuttering probably doesn't come from anxiety.

Stuttering usually starts in kids between two and five years old. It's possible to develop a stutter as an adult, but that's usually because of an injury or other condition— it doesn't normally show up by itself like it does in kids. The main symptom is the repetition of sounds and syllables— usually just one syllable, and that's often the first syllable of a longer word.

There are also other symptoms that can be harder to identify, like the lengthening of sounds, verbal or facial tics, or pauses in speech. One thing that can make stuttering hard to diagnose is that little kids often show these same speech patterns when they're learning to talk. It's normal for a kid to trip over words or get stuck on certain sounds, especially if their mouth can't keep up with what they're trying to say, and up to 20% of kids will show symptoms that look like stuttering.

But by the time they're four or five, 75% of them will have outgrown it. If someone is still stuttering by then, and if it's enough to disrupt their life or make them anxious, they'll likely be diagnosed with. Childhood-Onset Fluency Disorder, the official name for stuttering.

We don't know why some people outgrow their symptoms, but we do know that people don't start stuttering because they're shy or nervous. Being shy or nervous can make symptoms worse and can start a vicious cycle— because then you get more stressed and stutter more, and then you get even more stressed. But people who manage their symptoms score about the same on anxiety tests as people who've never stuttered, so scientists are pretty sure that it's not the root cause.

It's more likely that genetics is involved in some way. You're three times more likely to stutter if you have a family member who also stutters. It's also more common in boys than in girls, which is why some geneticists used to think it might be linked to sex-specific chromosomes.

But we now know that that's probably not the case. Newer research has found that mutations on other chromosomes, like chromosome 12, could be responsible. When researchers studied a group of families in Pakistan with a high concentration of people who stuttered, they found that 10% of those who did had mutations on chromosome 12.

That might not sound like much, but there were almost no mutations on chromosome 12 among those who didn't stutter. So, it's not a definite answer, but it's a useful clue for further research. Scientists have also found some neurological differences between people who stutter and those who don't.

For example, they've noticed in different brain scans that there are areas on the left side of the brain, which are usually really active when you're talking, that aren't as active in people who stutter. There are also regions on the right side of the brain that you usually don't use to talk, but that are overly active in people who stutter. This could mean that when you stutter, the right side of your brain is interfering with normal speech production on the left side.

That idea also supported by the fact that the corpus callosum— the bundle of neurons that connects the two sides of your brain— is a bit bigger in some people who stutter. When signals travel between the two halves of your brain, they pass through the corpus callosum, so having a larger one could help transmit the interference. But that's still just a guess—we don't know for sure why there's a size difference.

And, since kids' brains are developing at the same time as they're beginning to stutter, we don't know if those brain differences cause stuttering, or if growing up with a stutter is what makes the brain change. So, we still have a lot to learn about stuttering, and there is no cure for it yet. But plenty of people manage their symptoms with treatment.

One thing that helps is to make kids less anxious by teaching them that they haven't failed and that there's nothing to be ashamed of. Using direct instruction, like teaching them how some phrases sound, can also help, but another useful tool is to slow down the conversation— that way, the kid can get comfortable with simpler or slower sentences, and then work their way up to more complicated ones. The best treatment depends on the person, but there are a ton of ways to make stuttering less stressful and more manageable.

It's too late to help Newton, but as psychologists and neurologists do more research, we're starting to be able to help more of today's stutterers. Thanks for watching this episode of SciShow Psych, which was brought to you by all of our patrons on Patreon. If you would like to support the show and keep exploring all kinds of things about our brains, you can go to patreon.com/scishow.

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