Michael: One of our favorite things here at SciShow is to use our brains to debunk myths and pseudoscience, so I bet you can deduce what's really fun... That's right! Debunking junk science about our brains! Here are three videos that break down long-held, totally ridiculous theories about our brains, and then two videos that shine some light on just how amazing our brains really are.

First up: Victorian Era fake science. Because, why did people put any stock in phrenology?

Hank: A lot of exciting neuroscience was happening in 19th-century England. Victorian scientists were figuring out that certain parts of our brains are connected with certain parts of our bodies, like different senses or muscles.

But mixed in with all the legitimate research was some pseudoscience, or misleading ideas that spread without rigorous scientific backing. Like one theory from the Viennese physician Franz Joseph Gall, who thought that character traits, like religiousness or curiosity, were also linked to specific brain regions.

This theory became the basis of phrenology, a field of study that claimed that you could determine someone’s personality by the shape of their skull. Phrenologists believed that all human brains were made up of many distinct “organs” that could be mapped to personality traits. They claimed the more you used a certain brain region, the bigger it got, and the less you used it, the smaller it got — kind of like how muscles work.

And they assumed that the skull conformed to the shape of the brain, revealing where these bigger and smaller “organs” were. So, theoretically, you could inspect someone’s skull, and use a map of these “organs” to figure out parts of their personality.

Phrenology became enormously popular in the UK around the early 1800s, and spread to places like America, France, and Germany. It was pretty much a load of garbage and guesswork, and many scientists were vocal critics. But at the time, there wasn’t enough evidence to thoroughly debunk the theory.

Researchers would, of course, dissect the brains of dead people, not living people, and the human body changes a lot after death. So even if living brains were different shapes, dead brains probably looked pretty much the same.

Plus, the public thought phrenology was really compelling. Just like horoscopes, people tend to love things that tell them something about themselves. So, phrenology thrived on subjective validation, which is the idea that people tend to believe in something if it’s personally true or meaningful for them.

But as the ideas spread, they started being used to justify race and class inequalities. Upper classes used phrenology to reassure themselves that they were supposed to be on top, because of the ideal shapes of their brains. Lower classes, on the other hand, accepted the pseudoscience because it claimed that these brain “organs” could be developed, so they could improve themselves with hard work.

The American physician Samuel Morton made even more sweeping claims about skull shape in his book, Crania Americana. Morton argued that Caucasians were superior to other races, like Africans and Native Americans, because of craniometry, or different skull and supposedly brain sizes. Which is just racism under the guise of science.

Some phrenologists used these ideas to rationalize slavery and colonization, while others were anti-slavery because they thought these “inferior” races ought to be protected. Eventually, all this scientific racism was acknowledged, and phrenology’s legitimacy took a nosedive in the mid-1800s as we continued to learn more about how the human brain actually works.

First of all, the brain conforms to the shape of the skull, not the other way around. And secondly, the brain doesn’t physically grow or shrink like our muscles. Phrenologists were also wrong that the brain was made up of discrete chunks — it’s one organ with a bunch of networked cells.

But there was something to the idea that the brain was spatially organized, and different regions were linked with different functions — which we call functional specialization. The French physician Paul Broca contributed some evidence to support this idea in the 1860s.

He found that damage to the left frontal lobe in humans was linked to speech impairment, without affecting someone’s ability to understand what other people were saying.

In the 1870s, Gustav Fritsch and J. L. Hitzig were experimenting with stimulating different parts of the cerebral cortex of a dog, which produced movement in different areas of its body. Through experiments like these, scientists were able to develop a better understanding of different regions of the brain by the start of the 20th century.

Unlike phrenological maps, which assigned arbitrary brain areas to personality traits, our current brain maps are based on experiments that show different functions of each region. With the development of technologies like Magnetic Resonance Imaging and Computed Tomography, and the ability to do careful brain surgery, our understanding of neuroscience continues to grow.

Nowadays, we’re positive that phrenology was junk science. The shape of someone’s head doesn’t say anything about their personality, character, or moral depth. But we can still see its echoes in language we use today, like “highbrow,” “lowbrow,” and “well-rounded.”

Phrenology may have lacked scientific merit, and was definitely used to justify harmful ideas, but it did cause scientists to think more critically about how biology is intertwined with thoughts and emotions.

Michael: Those silly Vitorians! We modern intellectuals would never believe something so stupid, riiight? Well, have you ever heard that we only use 10% of our brain? That's still a pretty common myth. Here's Hank to rip it apart.

It's a notion that's been propagated by movies, magazines, and motivational speakers and repeated by well-meaning folks and shysters alike.

They tell you that you're only using 10% of your brain. If you're only able to access a fraction of your brain-power, just imagine what you could do if you tapped into all that unused potential! Read other people's thoughts, play the stock market, crush cans with your mind, and levitate!

Not to rain on your brain parade, but that 10% stuff is so far off that it would be laughable if it weren't so widespread, and I kinda can't believe I'm still talking about it! So like many myths, it's hard to pinpoint exactly where it began. There's no definitive source, though some have linked it back to the American psychologist William James and even Albert Einstein, who both suggested, in so many words, that we were only using part of our mental potential.

But the fact is, we is pretty much every part of our brains. A lot of it is active most of the time, whether you're reading a book, or listening to music, or walking around town or even sleeping. How can we be so sure?

For one thing neuro-imaging techniques like PET scans and MRIs actually let us see the brain in action. These images show as that nearly every region of the brain lights up during even simple tasks, like walking and talking. While we don't use all of our brain at once, just like we don't engage every single muscle at the same time, those scans prove that over the course of any given day you use just about all of your brain.

It also stands to reason that if 90% of your brain was useless, you could remove large portions of it, as you might an appendix or tonsil, and carry on as usual. Brain damage and disease wouldn't be as much of a concern if only 10% of the organ was actually functional. But in reality, there isn't a single area of the brain that can be damaged or diseased without resulting in some kind of physical or mental consequence, small or big.

You may have heard of the case of Phineas Gage, the 19th-century railroad worker, who wound up with a spike through his head because of an accident. It didn't actually stay in his head, it went all the way through and then kept going for quite a while.

It didn't kill him, somewhat surprisingly, and he still had his memories and his skills. But many of his friends reported that he had changed personalities. Now we don't actually know a ton about Gage, because a lot of people used him to try and prove a lot of different of points over the years, but there's little doubt that you can have a rod go through your brain and not have some things messed with.

Then there's Clive Wearing, the British pianist, who had a viral infection that destroyed his hippocampus, the part of the brain that controls the storage of memories. As a result he's no longer able to recognize anyone but his wife, and he can't retain a memory for more than 30 seconds at a time.

Every part of your brain has a function, and you need it in order to keep being you. And finally, we know that our brains are working all the time because we have to constantly feed them, literally.

The average human brain accounts for about 3% of a person's body weight, but it demands at least 20% of the body's energy to keep all those neurons firing. We're talking hundreds of food calories every day just so your brain can remind your heart to beat, or help you solve for X, or remember where you left your phone.

Our constant need for food, especially foods rich in fats and sugars, has a lot to do with our brains. And it wouldn't make much evolutionary sense for us to expend so much energy feeding a useless, wet lump.

So in the end, while telekinesis would be pretty awesome, our brains are already capable of truly incredible things. In fact, if anything, we only understand a fraction of what's going on up there, so instead of insulting its function, be thankful for all that your brain does, which is more than you know.

Michael: You know, I bet you're so smart that you use both sides of your brain, so why do we still try to compartmentalize people into being right-brained or left-brained? It's kind of complicated and cool. Here's an in-depth video about it.

There are plenty of personality tests out there that claim to tell you which side of your brain controls how you think, what you’re good at, basically, who you are. They might say that you’re a creative right-brainer, doomed to perform poorly in math and science. Guess you better give up on getting into MIT! Or they might tell you you’re a logical left-brainer, a regular Mr. Spock - terrible at the arts so, so much for Juilliard.

But, you may have noticed that there are more than just two types of people in the world... and they’re not all either scientists or artists. So there has to be some flaw in that whole left-brain/right-brain thing.

Even if you never bought into the myth, your high school textbooks probably taught you that the right half of your brain processes creative tasks, and the left half can handle math or form language. And that is a real thing! Different sides of the brain are often responsible for different tasks. It’s just that pop psychology has taken the idea a little too far.

It all started way back in the 19th century, when doctors realized that the two halves of the brain might not be identical. They noticed that when someone injured one side of their head, it affected some brain processes, like language or emotion, more than others.

But it wasn’t until 1961 that a neurobiologist named Roger Wolcott Sperry set out to fill in the blanks, along with a graduate student he was working with at the time, Michael Gazzaniga. Sperry’s research over the next few years would completely change the way the neuroscience community thought about the human brain. But in the process, he also accidentally created a myth that would plague popular culture for decades.

Sperry studied patients with severe epilepsy who had elected to undergo a surgery called a commissurotomy. This involved completely severing the corpus callosum, the bundle of nerve fibers that connects the two hemispheres of the brain and allows them to communicate with each other. You’d think that effectively chopping their brains in half would be a big deal -- and it was -- but the side effects, like problems with memory, were relatively minor compared with the benefit of not having seizures anymore.

Since the brain hemispheres in these patients basically went about their business independently, Sperry figured that studying them would be a great way to find out what happened on each side of the brain. All he needed were some simple tests. He already knew that the right hemisphere controlled the left side of the body, and the left hemisphere controlled the right.

So he and Gazzaniga devised an experiment in which they’d display an object on a screen to the subjects in such a way that it would only be processed by their right hemispheres. The best way to do that was just to make sure that only their left half visual field was seeing it. Because of the way the optic nerves are set up, that’s not the same as just covering the patient’s right eye.

Instead, Sperry had the patients focus on the center of a screen and then flash the image on the left or right hand side of the screen. The flash went by too quickly for them to follow it with both fields of vision. So when Sperry showed a picture of an object on the left side of their screens, he found that the subjects noticed it, but they couldn’t name it.

If that object was, let’s say, a picture of a key, their right hemispheres knew that they were seeing a shiny object, but they couldn’t come up with the word “key.” Since the subjects were lacking that connection between the two hemispheres, Sperry concluded that language had to be processed by the left side of the brain, which his subjects just couldn’t connect to.

He kept testing the patients with similar tasks that tested other basic processes, and eventually found a pattern: language and calculation seemed to be done on the left, and spatial reasoning on the right. Over time, that’s been simplified to logic on the left and creativity on the right.

But simplifying is not a great idea when dealing with something as complicated as a brain. Sperry himself described the results as “highly statistical,” just reflecting a general pattern, and not an absolute rule.

There even turned out to be some people who show the reverse pattern -- usually left-handed people -- and their mental capabilities aren’t any worse for wear. Still, his research was a huge deal at the time, and Sperry was eventually awarded a Nobel Prize for his work in understanding the specialization of the two hemispheres of the brain.

But even though he cautioned against generalizing his research too much, an article appeared in 1973 in the New York Times Magazine titled “We Are Left-Brained or Right-Brained,” describing Sperry’s research in oversimplified terms. Then there was an article in Time magazine that did the same thing. The rest is popular psychology history. A bevy of self-help books and personality tests soon popped up claiming that some people were guided by the logical left brain and some by the creative right brain.

So now there were two new ideas going around: one, that different processes occurred exclusively on different sides of the brain, and two, that people were more prone to one side’s strengths than the other. But only one of those concepts -- that each hemisphere controlled different processes -- was actually based on Sperry’s research.

Known as brain lateralization, the concept basically became neuroscience canon. And evolutionarily, there were a lot of reasons that it made sense. Like, it’s not efficient for both hemispheres to be required for us to perform every single task. Split up the functions between two hemispheres, and you can multitask.

Scientists were even able to test this using baby chicks. They found that chicks that tended to use their brain hemispheres separately managed to forage for food and keep an eye out for predators, but the ones with more distributed brain function couldn’t do both at once. In evolutionary terms, not being able to watch your back is bad news for a species.

There’s also the matter of brain traffic jams. The corpus callosum is something of an information bottleneck, which means that the brain has to be selective about what information it sends back and forth between hemispheres. Just like delegating tasks within a group of people, it’s much more efficient to let each hemisphere take responsibility for a particular job.

And finally, putting one hemisphere in charge of certain things just helps keep the peace in the brain. If both sides tried to process the same situation all the time, each would come up with completely different responses. Which would be... confusing.

So the concept of brain lateralization itself made perfect sense. But, turning the concept of delegating processes into the idea that some people could be left-brained or right-brained... Sperry never suggested that at all. Which is why, when in 2013 a group of American researchers set out to analyze over a thousand brain scans, they figured it might be time to debunk that myth, once and for all.

The researchers analyzed a type of brain scan called functional magnetic resonance imaging, or fMRI. fMRI shows the parts of the brain that are active by tracking the flow of oxygenated blood through different regions. The blood brings oxygen and nutrients to the more active parts of the brain, and areas with more blood flow show up as bright webs on the scan.

So the researchers looked at scans of over a thousand healthy, uninjured brains in what’s known as the resting state, where the subjects aren’t asked to perform any particular task, but there’s still brain activity because... they’re not dead.

If certain areas showed up brighter on the scan, it would mean that those parts of the brain were more active and interconnected. And if one whole hemisphere showed more bright areas than the other while the subject was basically doing nothing, that meant they probably had a dominant hemisphere. It would be evidence that some people were left-brained or right-brained.

Now, the researchers were expecting that certain areas lit up more brightly than others at rest. There are brain regions that are associated with things like using language and paying attention, and those did light up more. So it seemed that, even in the resting state, specific processes were divvied up between hemispheres, confirming Sperry’s findings.

But the scans didn’t show that one hemisphere was consistently showing up any more or less brightly than the other in the subjects. In over a thousand brain scans, they didn’t find a pattern of people who had more strongly connected right hemispheres than left, or left over right. As far as the authors of the study could tell, there are no Vulcans among us. In other words… there’s no such thing as an inherently left- or right-brained person.

Now, the idea of brain lateralization is still a really important development in our understanding of our brains. But it, too, is probably a lot more complicated than it’s often made out to be.

Like, even though particular tasks tend to be handled by different hemispheres, the whole point is that the two are constantly talking to each other to make even simple jobs possible. Ask someone to do something like invent a new word, for instance, and they’ll need creativity from the right hemisphere, but also language from the left.

So, people can still have particular intellectual talents, obviously. But being good at math doesn’t necessarily make you bad at writing fanfiction. I mean, you can’t have Sherlock without Watson. Or Bert without Ernie. Your brain is a duo, and it’s incredibly versatile. You may as well give it the credit it deserves.

Michael: OK, so skulls don't form around brains, we use our whole brains, and people aren't left- or right-brained really. But our brains are plastic? It turns out that brains learn in pretty fascinating ways. Check out this video about it.

You would not be here if you weren't interested in learning, and neither would I. But, here's something we haven't learned about together... LEARNING.

The ways in which we acquire and retain knowledge (which is the very definition of learning) is really a science in itself. And like any other discipline that involves the study of the human brain is practically still in its infancy.

Just twenty years ago most scientists believed that once we reached adulthood our brains were pretty much fixed not that we were incapable of learning anything new exactly, but the assumption was that our brains development phase was over... and now it's pretty much there to remind our hearts keep beating. And occasionally let us remember where we left our phone.

But thanks to huge advances in things like functional brain imaging we have a clearer picture than ever of how our brains work and we're beginning to observe some wonderful things. For one, we now know that the process of learning actually alters the structure of our brains at the cellular level and once more it turns out that our brains never stop changing to make room for new information.

People often compare the human brain to a computer, but imagine a computer that can actually grow new circuits, as it acquires new facts and associations (and you have a much more awesome comparison) -this is the gift known as neural plasticity. You might think of plastic is being stiff in cheap, but biology plasticity refers to the capacity of living things to mold themselves to new conditions and our brains are great at it.

For one thing your brain cells (or neurons) are always changing their connections to one another, to meet changing demands. Each of your neurons consists of a central body, with spindly dendrites and a long axon stemming from it. The neuron transmits electrical signals to other brain cells through its axon, and receives signals through its dendrites -via connections where the cells meet called synapses.

When you're born, each neuron in your brain has about 2,500 synapses connecting it to other cells. But by the time you're 3 and you've become just a sponge of fascinating new information like what sound a piggy makes & where your mom's face goes when she hides behind her hands... you have 6 times as many (up to 15,000 synapses) for each neuron in your brain!

In this regard it's kinda true that brain hit its peak when you're young, because by the time you're an adult your brain cells have about half as many synapses as when you were 3 but it turns out that's okay because we now know that synapses just shrink up when they're no longer needed. Like you know now that pigs go oink and that people still exist when you can't see their faces so you don't need to keep those connections to remind you. This process of winnowing down of unused connections is known as syntactic pruning.

Meanwhile, your neurons experience all kinds of new growth as you continue to soak up new information, like how to drive, how to solve for x, and how to get through that one really hard level in your favorite castles matching game.

Here... the key to learning is memory because you need to retain that information in order to apply it in the future. So your brain cells can change in different ways depending on how long you've remembered what you learned.

As you stockpile data in your short term memory, for example: the structure of your existing synapses has been found to change with more and stronger dendrites growing to reinforce them. So for info that you retain for just a short time-- like, how to destroy digital castles using rocks and fire you-- don't need to sprout whole new connections -just beefing up the existing ones you've used so far will help you master the game just fine.

But when it comes to important stuff like the learning we do at school or hopefully the stuff you learn here on SciShow your neurons actually forge entirely new synapses over time as you re-learn, re-remember, and reuse the information.

This is how your brain builds the long-term memory you need to retain the learning you're doing right now at work and at school and turn it into a lifetime of applied knowledge. So I said it before and I'll say it again take care of your brain and odds are... it'll take care of you! 

Michael: OK, one more video about some of the amazing things brains can do. This time, the three senses you might not even know you have.

At some point, you've probably learned about the five senses: sight, sound, smell, taste, and touch. But these five don't explain all of our sensations. How can we tell how hot or cold we are, or keep ourselves balanced?

Now, scientists are beginning to add more senses to that classic list. Here are three of them.

It's probably no surprise that sensing temperature is pretty important, which we call thermoception. It helps us keep our body temperature constant, and lets us know when our environment is too hot or too cold, so we can avoid tissue damage like from burns or frostbite.

So, how do we do it? Scientists have found a couple of potential mechanisms connected with the Transient Receptor Protein channel, or "TRP" family. There are lots of these channels, and they react to lots of different stimuli. We're still trying to figure out what they all do.

But one thing's for sure: A lot of them help us respond to changes in temperature. Scientists aren't exactly sure how these channels work, but with physical stimuli of the environment getting warmer or colder, depending on the channel, they're more likely to open.

One of these channels, TRPV1, plays a role in the sensation of painful heat. The receptor is activated when temperatures get uncomfortably warm, around 40 degrees Celsius. TRPM8, on the other hand, responds to cold stimuli, below 20 degrees Celsius, so pretty much anything below room temperature.

These channels, and others, can be found throughout our bodies. But when they're on nociceptors, or pain-sensing nerves, activation of the channel triggers a rush of calcium into the cell, and sends a signal to the brain about painful temperature. All that information goes to the Primary Somatosensory Cortex, a thick fold of tissue on the top of the brain where most of the mechanical sensations like touch, pain, and vibration are processed. Then, you can consciously process the temperature, and yank your hand away from that campfire, or decide whether you want to put on a jacket.

Now, have you ever thought about how you just know where your body is in space? Well that's proprioception. The word comes from the Latin for "one's own grasp." It's how you can type without looking at a keyboard, and walk without looking at your feet. And there are a bunch of specialized receptors in our skin, joints, and muscles, that help us do it.

For example, muscle spindles respond to changes in muscle length and the speed of muscle movement, while Golgi tendon organs send signals about muscle tension and exertion. And then cutaneous mechanoreceptors respond to stretch and pressure in the skin and joints.

All of these receptors work together to provide the brain, especially the cerebellum, with information about your movement and the positions of your limbs. The cerebellum is responsible for coordinating things like balance, posture, and voluntary movement.

Weirdly, though, scientists recently discovered a case of a woman born without a cerebellum, who has some balance and movement issues, but seems to be doing relatively fine. So there is still a lot to understand about how our brains process proprioceptive information. Separately, we have equilibrioception, our sense of balance, and we need balance whenever we move, like walking and running.

Ears are important for our sense of hearing, but they're also a key part of equilibrioception, especially the inner ear. It contains the vestibular system, which includes three fluid-filled semicircular canals, lined with tiny hair cells.

When your head moves, these hair cells are swashed around by the fluid and send signals to the brain, specifically to the vestibular nuclei in the brain stem. Each canal is responsible for a different kind of movement. One for up and down, one for left and right, and one for side to side.

The Otolith organs, located just below the semicircular canals, are similar, but in addition to liquid, they have tiny crystals made of calcium carbonate. As the head moves, these crystals rub against the hair cells attached to the membrane, which send information to the brain stem.

Your brain then sends information out to your eyes, joints, and muscles, so they can respond accordingly and help you navigate the world. Now, problems with this system can lead to issues with balance. Vertigo, for example, can be caused by loose stones in the Otolith organs. They can also fall into the semicircular canals, disrupt the normal fluid movement, and put unexpected pressure on the hair cells.

That pressure conflicts with what your eyes are seeing, which can make you feel dizzy when you move your head. Together, these three senses are really important in helping us navigate our environment successfully and safely, so even though they don't make the list of our traditional senses, I think we'd do ourselves a disservice by forgetting about them.

Michael: Thanks for watching this collection of videos on our incredible brains. If you want to learn more about the human mind and how it affects everything in our lives, check out our new channel, SciShow Psych. And special thanks to our Patreon patrons who make this channel possible and brought SciShow Psych into the world.