Reward pathway in the brain | Processing the Environment | MCAT | Khan Academy

– [Voiceover] Think about a time when you felt happy or particularly rewarded and this could be maybe
somebody gave you a hug or you received some verbal praise or maybe you just ate a particularly excellent piece of cake. In any of these situations, your brain is responding in a similar way. Even though you had different stimuli, they all indicated that
you were feeling rewarded. So what we’re gonna
talk about is the reward pathway in the brain. So this is your brain. Pretend you’ve sliced a brain in half and you’re looking at the
right hemisphere here. So here’s your brain
stem, prefrontal cortex, and the rest of it. So what I’m gonna focus
on is a few specific parts of the brain and when you first experience pleasure, your brain releases a neurotransmitter
called dopamine. So I’m just gonna write
dopamine off to the side. So the dopamine is primarily
produced in this area which is called the ventral
tegmental area or VTA. The vental tegmental
area is in the mid-brain and when it releases dopamine
in the reward circuit it actually goes to a lot of
different parts of the brain. So one of the places
the VTA sends dopamine is to the amygdala so
that’s kind of in this area. The amygdala deals with
emotions among other things. It also sends dopamine up to the nucleus accumbens which is around here and the nucleus accumbens controls your body’s motor functions. So then we also send dopamine up to the prefrontal cortex which helps focus attention and planning. And the last area that
we’re gonna talk about where the VTA sends
dopamine is the hippocampus which is kind of right around here. Just to note, that hippocampus
dot should probably be a little closer to the amygdala, a little more to the left. The hippocampus is in the temporal lobe not the brain stem. We’re just drawing it here
so it’s a little easier to separate out from the other parts that we’re talking about. And the hippocampus is responsible for the formation of memories. So now we’ve set up all
the parts of this pathway and what happens is
that when you experience a stimulus and the dopamine in the VTA is released and travels
along these pathways, it basically tells your body that this was good, let’s do it again so this is your natural response to some pleasurable stimuli such as food, sex, social interactions, also certain drugs, particularly stimulants such as cocaine or amphetamines
can initiate this response. And of course, different stimuli activate the circuit to different degrees and when we’re talking about drugs, that’s one reason that
some drugs are easier to become dependent on than others. They activate the reward circuit to a greater degree than others. The nucleus accumbens, the amygdala, and the hippocampus are all part of something called the mesolimbic pathway and as a side note, try not to get too caught up in the terms. These terms like mesolimbic pathway, mesostriatal pathway, sometimes they’re used
in slightly different ways by different people and sometimes they’re broken down into even more detail. Our purpose here is to hit the highlights, the really important parts
of the reward pathway so I’m just gonna use some of the more common terms. The mesolimbic pathway is a big part of the reward circuit in the brain. So what happens is the
VTA releases dopamine and it goes to all these different parts of the brain which have dopamine receptors so they uptake with dopamine and the result is a feeling
of happiness or euphoria which is the reward you get. So for example, the amygdala, which helps process emotions and is connected to the hippocampus, will say, “This was a
pleasurable sensation, “I enjoyed it,” and then your hippocampus will say, “Well, let
me remember everything “about this environment
so we can do this again.” For example, let’s go back to that excellent piece of cake
you might be eating. Your amygdala says, “This is delicious, “I love this, I’m feeling
so happy right now,” and your hippocampus says, “Well, let me “remember what restaurant I’m at, “what exact piece of cake I ordered, “who I’m with, let’s remember things “about this experience.” Then your nucleus accumbens, which helps control motor functions, says, “Well, let’s take another bite. “Let me use my hand to use the fork “to get another piece and eat it.” And your prefrontal cortex
helps focus on that cake and divert some of your attention to it. And then you take another bite and it’s delicious and the reward circuit goes crazy again and
the dopamine goes out, and that’s why you experience the sort of continued pleasure. And one interesting thing to note is that with the continued activation of this reward circuit, we talked about how dopamine goes up and at the same time a neurotransmitter called serotonin goes down and serotonin is partially responsible for feelings of satiation. So this is why drugs can be problematic when you continually activate this dopaminenergic circuit,
this reward circuit. Your dopamine goes up so you have this increasing sense of euphoria but also serotonin levels can go down which means you’re less likely to be satiated or content. What you might notice about this cycle is that it’s a very
biologically driven process. A long time ago, people used to think that drug addiction was completely driven by a failure or morals or willpower. And while people’s choices are definitely strongly involved, we
know now that addiction has physiological components as well. It’s similar to looking at
your family history to see if you might have a genetic predisposition for high blood pressure or something. If someone in your family
has high blood pressure or has suffered from a drug addiction, then you may have some increased risk to develop the same condition. However, environment and
your choices matter too so don’t worry, nothing’s set in stone. Some evidence for the biological basis of drug dependence actually
comes from animal models. Scientists could hook rats
up to IVs that give them cocaine if they push a
lever and when they do this, rats learn very quickly to push that lever and they’ll even engage
in drug-seeking behaviors and will increase their
dosage if they’re allowed to. What’s also really interesting is that negative consequences don’t
affect an addicted brain in the same way that
they do a normal brain. For example, when you
give a rat regular food that it likes paired with a substance that makes it sick, it
learns to avoid that food. It doesn’t like it anymore. But when you give an addicted
rat its favorite drug paired with a substance
that makes it sick, it still wants that drug. So whereas with the
regular food it learns that “Oh, something bad happened
when I ate this food, “I’m not going to do it anymore,” with the drug it says, “Oh, something bad “happened when I took this drug, “but I don’t really care,
I really need that reward.” And what those kinds of studies show us is that addiction seems to take over a rational mind. So what we’ll talk about in the next video is tolerance or how you get accustomed to certain levels of reward and withdrawal so how you react when those
pleasurable sensations are taken away from you.

Comments 62

  • I love you guys for putting up so much high quality content on Khan Academy Medicine. You rock!

  • Nice quick and succinct for the layperson..well done.

  • please, double-check hippocampus location

  • the voice was really pleasant to listen to as i am studying for a test and slightly stressed this was a relief..

  • Thank you, I am citing this on a paper I am writing and clarified a couple of points for me.

  • I think I'm addicted to your voice.
    Give me more!

  • Where can i find the study conducted on the mice,0? Its urgent

  • I am interested in  finding out info on dopamine deficiencies causes, effects and remedies ! Any suggestions are helpful ! Thank you!

  • Great video, you have blessed me with understanding.

  • How does the Striatum fit in to this picture. Why do Dopamine Agonists Increase Sex Drive, compulsive shopping, Binge eating etc.

  • Replication of the cocaine experiments in rats when the animals were in a stimulating, enriching environment did not duplicate the results of the studies that were famously done in the 80's.  Current thought is leaning more and more towards environmental factors playing a huge role in addiction and not just the brains pleasure pathways.

  • its great. ı appericiate for your sharing.

  • Thank you, and your voice is so pleasant 🙂

  • Great video. Thanks 🙂

  • Thank you very much for all your efforts. This is very useful even at an MSc level.
    I'm interested in the references you used. If you could provide it, that would be great

  • "Here's your brain stem, PFC… and… the rest of it."
    I knew this would be a good video from that point on.

    Nice summary though, saved me rereading about 6 lecture slides – result.

  • Great video – so helpful to see it displayed and explained in this way!

    Thank you!

    oh and i love your art 🙂

  • wow, I am speechless! thank u!

  • So helpful!!! Thank you!

  • Oh my gooooooodness; soooooo very helpful in helping me understand my own addictive behavior – one of those things being CAKE!!!!!! You did an amazing job creating this video!!!!!

  • didnt know serotonin dropped as dopamine levels rise? I know prolactin does, and prolactin is the one responsible for one feeling sated.

  • very very simple and useful!!

  • penis

  • so how come it takes me 3 seconds to process information? the dopamine wouldn't help that?

  • What does the MCAT mean in the title I am assuming it is some test that only occurs in the states?

  • Thank you for sharing this well explained information. I particularly enjoy they way the video is presented. The voice, pace and creative images are very well done 🙂 Useful information for anyone seeking to learn more about the brain.

  • the rat had a rat…ional mind

  • Like always, thanks heaps for the help.

  • This was so helpful. Thanks

  • wow. Very helpful. Easy and simple. Thanks a million 🙂

  • ( 02:05) How is Nucleus accumbens related to motor function? isn't part of the addiction and reward center? Thanks!

  • Has there been any research into the links between the face, particularly the eyes, mouth and cheeks and the pleasure centers in the brain? I have been developing exercises that stimulate a high quality euphoria, by constantly smiling to myself. Its is amazingly effective and has all kinds of positive benefits. Essentially I am become able to choose what turns me on to far greater degree than I was able to before.
    You have physically smile, but also put the smile 'feeling' in as well, a çold' smile won't work. the only limitation is the power of your concentration. If anyone wants to try the basic exercise is to smile into your own eyes in a mirror. If the mirror is not so well lit it is better. You only want to see the outline of your features or you may get to involved in worrying about unimportant details. after you have learned how make your feel happy this way, try using the same trick in other circumstances until you can smile about practically anything you want to. If you are doing it right you will notice a great improvement in the way your face looks, you will become younger and more beautiful.

  • Hahah, this was funny to watch. It's kinda late at night here and it helped me to wake up while I continued reading for my Step 1/medschool exams. Love your voice as well.

  • Great video

  • Does anyone know why they serotonin levels drop? Does dopamine play a direct role in the decrease in serotonin?

  • Great video. Really useful for review after a few years. Just to check my understanding, isn't dopamine more associated with attribution of salience to stimuli, whilst happiness, euphoria, a pleasurable response etc. attributed to co-occuring release of endogenous opioids?

  • I am so happy to find this!

  • Is it possible to pharmacologically increase dopamine in the Nucleus Accumbens without also increasing it in the Ventral Tegmental Area?

  • nucleus accumbens does not control bodys motor functions it's involved in the reward pathway. What it does do is integrate motivation with some sort of action.

  • Thanks for excellent videos! Easy to digest information for a jabroni like me to comprehend/retain. These videos have been both helpful and applicable in my life.

  • your voice increases secretion of dopamine from my VTA

  • This is sooo informative in a very simplified way. Thank you

  • i get hugs from trees

  • Yep, leave it up to science, for the solutions for a better future… for THEM, as they remove any will towards higher pay, or even getting paid at all!  Then they would have a free workforce, and military and that's what I believe the Mark of the Beast will be, the removal of free will through an implant!  God gave us free will to accept Him, or reject Him, and if we accept the Mark of the Beast is the same as giving up our free will!

  • Thank you so much, the video was very clear and not bombarded by overly confusing jargon. The person teaching was also very clear. 🙂

  • great vid,

  • this is probably the simplest way to explain exactly how i respond to my environment and why i do the things i do, or even how, rather. Everything we do is associated to our impulse brain reactions.. the results we get from the things we do release certain chemicals that either make you feel good… or perhaps not so good.. so if everytime you do something, you get a negative experience or result… sooner or later your brain will associate that event/experience to negative emotions… and so now we have a motivational issue. I used the down side of this to exemplify because most people always talk about only the positive things when they refer to how people react to their environment. This is why this is a very big challenge for me.. its not just a choice i have to fight perceived lived experiences every step of the way… and that is why i have to take time to process my environment. Im not being difficult.. it is livably difficult for me…. even if its something that i really want. That's why i have to go about things in a different way… thats why im always in my head. It doesnt help that I am already over analytical.

  • good expalanation. kindly provde me the list of references you covered the topic from…

  • Thank you for this wonderful video. I also sincerely hope the scientific community can find an alternative way to conduct research on instead of innocent animals. Onc can argue it is for the greater good, but it still breaks my heart.

  • thanks for the class, very helpful, nice drawing and sweet voice.
    I really didnt know serotonin levels go down when dopamine rises, i used to take prescription medicine to rise serotonin levels when i was a teen due to genetic reasons (guess i was born like that), and now im watching this cuz i think i damaged it all again due to cannabis addiction.

    like you said nothing's set in stone. thumbs up.

  • love the voice!

  • No, Nucleo Accumbens does not control the motor functions it controls how pleasurable that experience was, so whether or not it's good, or all the euphoria you feel or happiness comes from there.

  • What a soothing voice x

  • Prefrontal cortex… and the rest of it. Very high quality

  • I love the voice!

  • exciting science gets me aroused

  • Here's your Pre-Frontal Cortex…..and……the rest of it.

  • which part in the brain activated the ventral tegmental ? amygdala or hypothalamus


  • This video explained some life changing information. I highly appreciate it

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