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MLA Full: "Why You Always Have Room for Dessert, and Other Weird Experiences EXPLAINED!" YouTube, uploaded by SciShow, 9 June 2021, www.youtube.com/watch?v=ioctkVCEan8.
MLA Inline: (SciShow, 2021)
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Chicago Full: SciShow, "Why You Always Have Room for Dessert, and Other Weird Experiences EXPLAINED!", June 9, 2021, YouTube, 30:33,
https://youtube.com/watch?v=ioctkVCEan8.
Have you ever wondered why you're too full to eat another bite of dinner, but you somehow find room for a whole piece of pie? Turns out there's a scientific reason for that! Join Hank Green for a fun new compilation from SciShow Psych where we dive into these weird human experiences, and find out just what causes them to occur!

Did you know we have a whole channel dedicated to the human mind, people and interactions between people? It’s called SciShow Psych! https://www.youtube.com/@UCUdettijNYvLAm4AixZv4RA
Check it out!

Hosted by: Hank Green

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at http://www.scishowtangents.org
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#SciShow

 (00:00) to (02:00)


Intro [Hank]: If you're watching this, you are probably a human, and we have a show that is all about you.

It's called SciShow Psych, and there we talk about the human mind and people and interactions between people, and on that channel, we've explained common human experiences like riding a bike or forgetting what you were doing when you walked through the door, which might seem like simple things, but our brains always find a way to spice things up. So today we thought we'd share with you some of the weird, fascinating reasons behind simple things that a lot of us experience, and if you like it you can check out Youtube.com/SciShowPsych for more.

We're going to kick things off with doorways. Have you ever walked into a room and forgot why you walked into that room. This is not just you, and you can blame your brain.

Here is Brit one of our show hosts on SciShow Psych with more about that. [Title card: "Do Doorways Actually Make us Forget Things?"] [Brit]: Does this sound familiar: You get up to grab your phone, or a cup of tea, or something else in the other room but once your there you have absolutely no idea why. Were you distracted? Sure, maybe, but it could also be because you walked through a doorway.

Yep, according to Psychologists at the University of Notre Dame, something as simple as walking through a doorway can make you forget things. They found this out by testing undergrads in the lab. They asked students to place six blocks of various shapes and colors in a shoe box, cover it with a lid, and carry the box across one big room or into another room.

There, the students were quizzed on the contents of their boxes. Had they carried a yellow sphere? What about a green cube?

Most people could remember the objects most of the time, but when participants had walked through doorways, their performance was consistently worse. Something about doorways seemed to make them forget. This happens with not only real doors but in virtual environments, too, and even when people are asked to simply imagine crossing a threshold.

It's called the location updating effect, or more simply the doorway effect. (2:01)

 (02:00) to (04:00)


You might think this is just a case of context like if you walk back into the original room maybe that can help you remember, but The Notre Dame Scientists tested this and that didn't make participants any less forgetful.

The forgetting wasn't just about being in a different room, the act of walking through the doorway was the culprit. So what's going on?

The best explanation has to do with how our brains process events. After all, you can only think about so many things at once. Working memory, our neural representation of what's currently happening is limited.

So the best way for our brains to deal with everything is to break it into chunks. According to this theory, known as the event segmentation theory, our brains create representations of events called event models which let us predict what might come next at any given moment like if you see someone tie one shoe, it's a pretty safe bet that the next thing they're going to do is tie the other one. But these event models need to be updated as the circumstances around you change.

Once someone's done tying their shoes, for example, having that model in your head isn't very useful. And that's where doorways, and other so-called event boundaries, come in. Doorways are a sign that something's changed and maybe you need to refresh.

The problem is that when your brain updates the status report, that old information isn't as accessible, even if you still need it. Psychologists also think people might have a hard time remembering things like those colored blocks in the experiments because they create two event models with those objects, one for each room. So, when it comes time to retrieve the information about what's in the box, or what you went into the other room to find, the two models compete and interfere with each other.

But, this whole system that your brain has for processing things still is useful, even if it sometimes leaves you in the kitchen wondering why you're there. That's because more often than not, passing through a door does mean that a new event is beginning, which means that it's okay to dump all of the information about the old event. So, this kind of event might be annoying but isn't really a bad thing, and it's not a sign that you're getting old or developing dementia.

Scientists actually checked this, and the doorway effect was just as strong in college students as it was in a group of older people. In fact, event boundaries like doorways sometimes might even help you remember. In a different experiment, the same Notre Dame psychologists challenged students to remember a list of words that was read aloud, half in one spot and the other half in another room or the same distance away within the same room.

 (04:00) to (06:00)


The test subjects remembered more of the words when they crossed through a doorway than when they just moved to another part of the room. Here, the doorway was beneficial. By divvying up the words in two separate event models, the brain can structure the information better and take more of it in. So, if you end up in your kitchen baffled by why you're there, don't worry, your brain made a tiny mistake. In the grand scheme of things, it's doing things just right. 
[Transition]
Hank: So physical doorways give an instant refresh to your brain and you forget what you were going to do in the first place. But what if it's not a real memory, but a dream? Why is it so hard to remember those? Like, we just wake up and poof, it's gone! That said, this also might just be me. You might be better at remembering dreams, or worse than me. Why is this? Well, let me explain.
[Transition]
Hank: It seems like some people can regale you with every last detail of the dream they had last night, while others can't remember whether or not they even had a dream. No matter which camp you fall in, everybody does have dreams, it's just that some people are better at remembering them than others. And whether or not you remember those surreal, unconscious experiences has a lot to do with the activity in your brain and with how well you sleep. Scientists still aren't totally clear on why we dream in the first place, but they have a decent idea of what our brains are up to when we do. We dream the most when we're in a state of sleep called REM. REM stands for rapid eye movement, and it's a stage of deep sleep that gets its name from the way our eyes move back and forth while we're in it. We typically have a few REM cycles through the night, beginning around 90 minutes after we fall asleep, and each cycle can last between a minute and an hour. Even though you're sleeping deeply during your REM cycles, your brain actually acts a lot like it does when you're awake. For instance, while you're awake there is a lot of blood flowing to the cerebral cortex, the thin layer that surrounds the largest part of your brain, which plays a role in making decisions and thinking creatively. (6:08)

 (06:00) to (08:00)


Blood is also flowing to the limbic system, a set of structures that control your emotional response to the things you experience. During REM sleep, those same parts of the brain are active, even your heartrate and blood pressure are similar to what they are when you're awake, so you're having lively, emotional experiences a lot like the ones you'd have when you're awake.

The main difference is that while you're asleep, your brain kindly paralyzes you so that you don't act your experiences out. They can still feel very real, though. So during REM, almost everyone is having dreams, and often vivid ones, but not everyone remembers them.

In part, that's because some people just have more brain activity during REM sleep. The more blood you have flowing to the cerebral cortex, the more active that part of the brain will be. More brain activity creates more vivid dreams, and more vivid dreams tend to be more memorable.

But another big reason you either remember your dreams or don't has to do with your levels of a hormone called norepinephrine. Whether you're awake or asleep, norepinephrine helps you remember things. Whenever you have an emotionally stimulating experience, your brain releases this hormone.

As it rushes through your brain, it binds to the nerve cells that help us learn new information, creating pathways between them. Later on, electric signals in your brain can travel back down those pathways to help you recall the experience you were having when they formed. So norepinephrine is always present at some level while you're awake.

When you fall asleep, though, your norepinephrine levels drop. That's true for everyone, and it's especially true during REM cycles. But from then on, the amount of norepinephrine in your brain has a lot to do with how well you sleep.

If you knock right out and don't wake up 'till morning, your norepinephrine levels probably rarely rise to the point where you start creating memories. (8:01)

 (08:00) to (10:00)


But if you're a light sleeper, you likely get a little rise in norepinephrine every time you stir awake. And that norepinephrine helps your brain cells create connections that make you more likely to form a memory of the dream you were having. So being able to remember your dreams isn't exactly the superpower it might seem like. The truth is, you probably just don't sleep very soundly.

And if you've never been great at remembering your dreams, that's not a bad thing. But if you're really curious about the places your subconscious minds wanders you sleep, there are things you can do to get better at remembering.

For instance, right when you wake up, you can keep your eyes closed and attempt to think back on what you've dreamt as you gradually become more conscious. Since you're slowly entering awake mode, you'll be more likely to retain the memory. That's because when you wake up abruptly, your levels of cortisol, the body's stress hormone, tend to take over and focus you on the day ahead, which gets in the way of your brain forming memories. So when you wake up more slowly, you have a better shot.

And then you can also do this trick. You can just drink a lot of water before bed. If you keep having to go to the bathroom, you will get the benefit of the norepinephrine rise each time you drag your foggy-brained self out of bed.

And if you do manage to remember something from a dream, you might want to write it down before you fall back asleep. But even if you never remember anything, you can be pretty sure that your subconscious self is still having lively adventures while you sleep.

But there are somethings that you don't need to write down. You remember them by heart, just like riding a bike. If you learned as a kid, no matter how long ago it was, you can probably grab a bike and ride it, no training wheels required. Now, this all comes down to how your brain stores those precious memories.

One again, here I am to explain.


 Memories (9:50)



If you learned to ride a bike as a kid, at some point, you probably left the bike in the garage for months or years before coming back to it. And though you might have been a little wobbly when you finally decided to climb back on, you never had to go through the training wheel phase that you had at the start. (10:04)

 (10:00) to (12:00)


That feeling is so familiar, it's become a figure of speech- when something is easy to remember after a long time not doing it, you say "it's like riding a bike". But this kind of memory really does stand apart from other kinds. Even when people suffer memory loss, memories of how to do things, often survive. So why is riding a bike, "just like riding a bike"?

Motor memories get stored differently than lots of other memories, making them harder to lose, but like other memories, there's still a lot we don't know. Motor memory is the ability to repeat motions and remember motor skills. It's part of a category of memories called "Implicit memories", which are generally things you learn less by thinking, and more by doing. And when you learn things without putting in specific effort to learn them, weird things can happen.

Like back in the 80s, 48 students were asked to identify what was in some incomplete photos, some they have just seen the full version of, but others were completely new to them. But then, 17 years later, researchers got in touch with 12 of them, brought them back and compared them to a control group who had never seen any of the pictures before. Those 12, still did better at identifying partial photos when they hadn't seen the full version in 17 years, while the control group didn't show any difference. 4 of those 12 students also said they had no memory of even being in the study, which is part of what makes it implicit. No one ever sat them down to make them study up on photos because they were going to be tested later, like you might for a test in school. 

Those implicit memories also use different brain systems than other kinds. One of the first on any list of brain parts related to memory, is probably the Hippocampus, which is involved in making new memories. But it's less important for implicit and motor memories. (11:55)

 (12:00) to (14:00)


One reason we know this is from studying patients with amnesia. When people suffer injuries to the Hippocampus and nearby parts of the temporal lobe, they tend to lose memories from before the injury, and also can't make new memories afterward. These are called Retrograde and Anterograde amnesia, respectively. And while it would be, of course, massively unethical to cause brain damage in order to study memory, case studies of people who have suffered brain injuries can give us unique insight. 

Basically, if someone damages a part of their brain and loses a certain function, you know that part was necessary for that function, and some of these cases have interesting twists. For example one patient spent years volunteering to shelve books at his library after a motorcycle accident caused him to lose his hippocampus preventing him from making new memories, but he still learned the Dewey Decimal System, even though he couldn't tell you how he learned it. Which means that researchers have to look beyond the hippocampus to understand how implicit memories work, and for motor memories in particular, we got a few leads. 

One of these regions is the Cerebellum, that's a part of you brain that's separate from the cerebral cortex. Other brain regions involved in memory like the hippocampus, are part of the cerebral cortex, so the fact that it's separate might be part of why this learning can be unconscious. And one of its major purposes seems to be fine tuning of motion, that includes careful movements, like balancing on a bike or playing the piano.

It's a complicated system but some of the tools that make it all work are called Purkinje cells. They collect signals from neurons coming from other sensory systems, like sight and sound, and convert them into a signal that fires at a variable frequency, up to 500 spikes per second. That signal gets sent to different motor systems, like hand grasping or gait, hopefully adding up to a smooth, fluid motion. One of the mysteries though, is that this might not be where these memories are stored. Instead research has pointed to changes in a number of different brain regions, not all of which are where we'd expect. (13:53)

 (14:00) to (16:00)


[Hank]: For example in a study published in Nature in 2004, 24 people were split into two groups; one of which was asked to learn how to juggle. After about three months of practice, they all could juggle for a solid 60 seconds.

The researchers scanned their brains and found changes to the temporal lobe and the intraparietal sulcus in the group who learned to juggle.

These weren't regions associated with memory per se, instead they had to do with tracking visual motion and planning hand movements. But then three months after that, the volunteers got their brains scanned again, and those changes were still there, though they were a little smaller.

That's even though none of them reported continuing to practice. I guess once the scientists tell you you're done you just stop juggling.

Come on! have some fun!

But similar studies found other brain locations were important so we probably won't ever tie motor memories to just a single location or process.

And those neurons in the cerebellum might not be just for motor skills, there's evidence some cognitive tasks require them as well, some research has even tied them to emotional experiences.

So the next time you get back on your bicycle give some thanks -at least in part- to your cerebellum, it's one of the major things keeping you balanced and upright and contributing to your ability to hold on to that for years.

[Transition]

[Hank]: But something that your brain does not have is a key holder. Which might be why I lose my keys all the time. I literally- okay. I put them right there. They are right there. They're on the little stool.
But why does this happen so frequently?
 
Here's Brit back with more.

[Transiotion]

[Brit]:It's the most annoying thing: You're about to walk out of the house when you realize you have no idea where your keys are.

They're not on the little hook, by the door, where you're supposed to put them of course, and though you tear your place apart it takes you, like, 30 minutes to figure out where you put them.

Frequently losing things like your keys is one example of Everyday Forgetfulness and psychology can explain not only why it happens but also some ways you can combat it.

Don't worry! Losing something like your keys is not a sure sign that your memory is going. (15:53)

 (16:00) to (18:00)


Anywhere from one third to one half of young people consider themselves forgetful. Doing things like frequently misplacing objects or forgetting names or faces.
 
And these little "Cognitive Failures" don't have anything to do with your intelligence either, their frequency and severity don't correlate with things like general cognitive ability or iq; and psychologists stress that they stem from absent-mindedness, not a lack of intellect.

Really if anything, how often you lose your stuff could be more tied to your genes than your smarts, age or health.

About 50% of the variation between people can be traced to genetic factors. For example scientists have found a link between benign memory lapses and certain variations in the gene that encodes for the dopamine D2 receptor or DRD2.

Not to be confused with r2d2, this is a protein that binds the neurotransmitter dopamine and it's heavily involved in the cellular communication that occurs when you try to recall where things are.

Other small gene changes have similarly been linked to forgetfulness, but it's not all predetermined. How you think about your memory problems may also have an effect. 

According to research people who believe they have control over their memory tend to be less forgetful than those who think forgetfulness is just an irreversible part of getting old.

Studies also find general support for the idea that memory training and learning specific strategies can improve your recall. This all makes sense when you break down what's actually happening in your brain when you forget where something is.

From a psychological perspective losing your keys means one of two things happened: You've either failed to recall where you put them, or you never knew where they were put in the first place. The latter can happen if you're not paying attention when you set them down.

To remember information you have to do what psychologists call "Encoding". That's where you store the information you've just gained -like the location you're putting your keys- into your brain's short-term storage or "Working Memory".

You simply don't have enough storage space to remember every sight, smell, sound and feeling. So only the things you selectively focus on in the environment -those that are given your attention- can get stored.

That means if you're not paying attention when you set down your keys, say you're hungry and thinking about what you might have for dinner instead, then you'll never remember where they are. You didn't actually store that information in your brain to begin with.

The good news is psychologists say that simple things can actually help with this.

 (18:00) to (20:00)


Like, as silly as it sounds, you could announce out loud where you're putting your stuff.

[Imitating British accent]
"Hear ye! I am putting my keys on the counter!"

Or, at least, take a moment to really think about where you're putting them and why. That way, there's something to remember later when you need to find them.

Your forgetfulness might also stem from the other end of things. The whole "remembering" bit. For example, you might just be remembering the wrong thing since recollection can be impaired by something called "interference." Basically, when you try to remember where your keys are, any memories you have of ever setting them down can compete to be the one recalled.
 
So, if you constantly move your keys around, you might remember them being on your dresser, on your coffee table, or by the door, which makes it tougher to remember which place you actually used last.

People who are less prone to everyday cognitive lapses, whether because of genetics or otherwise, don't tend to have this problem as often. They're better at remembering the right spot and forgetting the others - a phenomenon called "retrieval-induced forgetting."

But for those of us who aren't so awesome at that, psychologists recommend having a dedicated spot for things you often lose - like a key-hook by the door - which can help cut down on interference. And if you make hanging your keys automatic, then there's also a good chance they'll be on the hook even if you didn't take the time to focus on where you put them.

Admittedly though, relying on automation could make it harder to remember where things are if you don't put them where you're supposed to because of that whole "attention" bit.

So, maybe the best way not to lose your keys is to have a dedicated spot and to always be very attentive about putting them there. Like announcing, [imitating British accent]"Hear ye! I am hanging my keys on the hook!" while you do it every time you get home. I never said the tricks to not losing your stuff were cool. [short laugh]

If you want to improve your memory in general, you could also try exercising regularly and getting enough sleep. Both have been tied to better cognitive performance and less forgetfulness, though results vary.

And if you still can't find your keys, you might look into one of those remote-finder-things that you can slip on your keychain. Eh, whatever works, right?

[Intro Slide: SciShow]

[Hank]: But what happens when you try to remember what you did yesterday or last week? I can barely remember what I had for breakfast yesterday, but our brains aren't tape-recorders, and they don't always preserve -

 (20:00) to (22:00)


[Hank(continued)]:  - a flawless record of what we see and do.

So, am I remembering what I had for breakfast yesterday, or am I creating a false memory of those Cheerios and that banana? Let me explain why your memory can sometimes be a tricky thing.

[Title Slide: How Your Memory Can Be Tricked?]

[Hank]: It's easy to assume that your memory works like a camera. We know how cameras work, so it's like how memories work: you take snapshots of your life and sometimes it's hard to find a picture or you accidentally delete one, but the ones you keep are a good record of what actually happened.

But psychologists who study memory actually think it works more like a Wikipedia page: you can trust it as a general reference, but every time you remember something, you can make changes to it and so can other people. In fact, there are lots of ways your mind can be tricked into thinking things happened that never actually did.

One way is through suggestion - basically dropping hints that something happened a certain way. The psychology study in the 1970s was one of the first to show the power of verbal suggestions.

In one experiment, the researchers played college students videos of a car crash, and then asked some questions about the crash.

One group was asked how fast they though the cars were going when they "hit" each other, another was asked how fast the cars were going when they "smashed" each other, and that word choice affected their memory.

When the researchers said "smashed" instead of "hit," people's estimates of the speed increased by about 3 miles per hour. Then, when the psychologists followed up about a week later, they asked if the participants remembered seeing broken glass in the video - which, for the record, there wasn't.

Of the 50 people who heard the word "smashed," 16 remembered seeing broken glass that wasn't actually there as opposed to 7 of the 50 people who heard the word "hit." Even without the suggestion, a few people were remembering incorrectly but not as many.

Now, that wasn't a huge study, but the power of suggestion has been replicated hundreds of times in different experiments, so it seems like we're pretty prone to getting little details wrong. Turns out, we're also bad at remembering where we heard something in the first place or whether something actually happened to us instead of, like, dreaming it up - this is known as "source misattribution."

 (22:00) to (24:00)


In one study, psychologists tested for this effect by inviting some 210 volunteers into a lab for a couple of days and asking them to either do or imagine doing a bunch of different things. There were familiar tasks like smelling a flower, plus some weird ones like tapping a flower to their forehead. Then, two weeks later, they were asked to remember what they did. It didn't matter if it was something normal like rolling dice or strange like sitting on dice, over half the time, participants thought they actually did the things they only imagined. And if they spent more time imagining an action, they were more likely to think they really did it.

Now, both of these memory flaws have been psychologists sort of messing with people, but sometimes we just unintentionally make stuff up. These are called "spontaneous false memories." This is when all the knowledge and patterns you have swimming around in your brain can mess up what you remember. Let me show you.

Try to remember this list of words [list appears @ 22:53] - think ya have 'em memorized? Good. Now take a look at these words - how many of them were on that first list? In case you were wondering and didn't just write them down, the answer is six. But in controlled lab experiments where people do have a little more time to memorize, most people will falsely remember one word that wasn't on the first list - "window."

That's because the first list was basically a bunch of window-related words, so it's easy for your mind to make a goof. This example is called a "DRM List" named after the psychologists who wrote and studied it: Deese, Roediger, and McDermott.

But spontaneous false memories can happened in all kinds of situations. For instance, one study showed children between 5 and 12 years old different versions of a video where a teacher read a story to a class and then got money stolen from her wallet in a cafeteria. Then, they had to pick the thief out of a lineup.

In one version of the video, there was a bystander next to the teacher while she was reading, someone who was about the same age, build, gender, and ethnicity as the thief. And after watching that version, the 11 to 12-year-olds were more likely to pick the innocent person out of the line up than the actual thief. This is called

 (24:00) to (26:00)


"unconscious transference," when an innocent person gets misremembered as a criminal because of the way your mind categorizes things like how they look.

Psychologists think we make up these patterns as we go through life, most of the time without thinking about it. They've also noticed that adults usually show unconscious transference and mix up DRM Lists more than really young children do because they just have more life experience and general knowledge.

So, memory is kinda scarily unreliable, and it's probably worth taking your own memory worth a grain of salt. But now that you know some of the ways your own mind can trick you, maybe you can avoid being too trusting. You know, "Pics or it didn't happen."

[Slide: SciShow]

[Hank]: But beyond our memories, our stomachs can also be tricked. Kinda. Like it doesn't matter if I created the memory of those Cheerios and banana, I always find room for dessert. Well, it turns out I'm not creating an imaginary second stomach - it's my brain helping me find some extra space. Here's Psych host, Anthony, with more.

[Slide: Why Do You Always Have Room for Dessert?]

[Anthony]: It's happened to all of us: dinner is over and you're stuffed, but then someone brings out the pie and ice cream, and while a moment ago you couldn't have eaten another bite, suddenly - well, of course you can find room for a little pie.

And it's actually kind of true that you always have room for dessert, and it has to do with how our bodies evolved long before dessert existed the way we know now. But once you understand why you always have room for dessert, you'll see how you can use this weird quirk of your appetite to your advantage.

When it comes to our appetites in general, humans and other animals tend to get less pleasure out of eating something the more they eat it. This is called "sensory specific satiety," and it's an example of habituation. Whenever you encounter some stimulus over and over again, your response to it goes down. It's like when you hear a great new song for the first time and you love it, but then after a few months of hearing it on the radio, you're just completely over it. Our brains react the same way to food.

At first, a new food is really rewarding, but eventually, your brain-

 (26:00) to (28:00)


- eventually, your brain gets tired of it. And neuroscientists have actually watched that happen in real time.

In a 2001 study published in the journal Brain, experimenters gave nine subjects a series of chocolates and scanned their brains while they ate them. After every piece, the subjects rated how much they enjoyed the snack and how much they wanted another. Even though they were eating the same kind of chocolate each time, both of these ratings kept going down with every passing piece.

Not only that, but their brain activity changed, too - specifically, in their orbitofrontal cortex, which processes sensory and emotional information. In one spot, there was less activity over time, suggesting it was reacting to how rewarding the chocolate was. But in another spot, there was more activity, suggesting that it was a sign of an increased sense of revulsion or punishment. To chocolate! Because it had just had enough. And a number of studies have shown similar results.

When people fill up on one thing, even if it's something they like, they begin to feel repulsed by it. But even if they can't stomach any more of that one thing, their brains don't have the same reaction to other food. So when it comes to finding room for dessert, something similar seems to be going on.

See, if you've had a well-balanced meal, you've probably filled up on vegetables, proteins, and complex carbs, so your body's had enough of that. But dessert is different. It doesn't have a lot of those things, and it usually has a lot more sugar, and your brain's not tired of that yet, so suddenly, you're not as full as you thought.

As weird as that seems, it might have been kind of an advantage from an evolutionary perspective. We don't know exactly why we evolved this trait, but in the past, the fact that we sought out variety might have meant we were better at eating a balanced diet and weren't missing key nutrients.

There's also one other factor that makes it especially easy to make room for dessert - dessert just doesn't fill you up the same way as other food. Typically, you know you're hungry because your stomach releases a hormone called "ghrelin," which alerts the brain that you need food. Then, as you eat, the amount of ghrelin in your blood goes down, -

 (28:00) to (30:00)


- ghrelin in your blood goes down, and you start to feel less hungry. But that change and the amount of ghrelin depends on what you've eaten. 

Complex carbs and proteins cause a significant drop, but sugar barely changes your ghrelin level at all. Eating just simple sugars is almost as insignificant to your appetite as drinking water. And let's face it - most desserts are basically sugar - so not only is your brain not tired of it, but as you eat, dessert just doesn't fill you up as much.

Your body does have other ways of informing you that it's full, like by using special receptors to sense how stretched or contracted your stomach is, so eventually you would feel full no matter what. But if you're still feeling betrayed by your brain for letting you eat more dessert than you intended, think about it this way - you can also use all of this to your advantage.

For example, sensory specific satiety does make it easier to squeeze in dessert, but you can also take advantage of it to squeeze other foods into your diet. Like, maybe you bought something healthy for snacking, like a bag of almonds, but now you're just tired of those, and the junk food is calling to you. Well, if you have a variety of healthy snacks, you have a better chance of actually wanting to eat them.

In a 2013 study in American Journal of Clinical Nutrition, researchers tested a similar thing on kids. During pre-school snack-time, they put out different fruits and vegetables and tracked what the children ate. If they just put out one kind of fruit or vegetable, about 70% of the kids took a snack. But if they put out a variety, 94% did, and they ate about three more pieces of fruit on average. So, if you've ever struggled to get a picky kid to eat more vegetables, variety might help.

And when it is time for dessert, if you're trying to scale back, you can try to avoid eating sugars on their own. Like you could have ice cream with fruit or add oats to your cookies, and it may help you feel fuller for longer.

If nothing else, it's good to know that it's not your imagination. Your body really does react a little differently to dessert at the end of the meal. And at the very least, knowing -

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- how it works might help you trick yourself into eating a little better.

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[Hank]: It seems like our memories love to play tricks on us - whether it's dumping everything when we walk into the kitchen, or making something up on the spot.

If you enjoyed these amazing things that your brain does, go on over to SciShow Psych at https://youtube.com/scishowpsych where we answer questions like these and many more, and we would love to have you as a subscriber.

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