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Current time:0:00Total duration:8:26

Reward pathway in the brain

Video transcript

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 was responding in a similar way even though you had different stimuli they all indicated that you were feeling rewarded so what we're going to 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 want to 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 going to 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 ventral tegmental areas in the midbrain 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 you make delete deals with emotions among other things also sends dopamine up to the nucleus accumbens just around here and the nucleus accumbens controls your body's motor functions ok and so then we also send dopamine up to the prefrontal cortex which helps focus attention planning in the last area that we're going to talk about where the dopes the BTS ends dopamine is the hippocampus so it's so it's 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 brainstem 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 all right so now we've set up all the parts of these this pathway and what happens is that when you experience a stimulus and the the dopamine and 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 this 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 methyl mezzo limbic pathway as a striatal 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 the really important parts of the reward pathway so I'm just going to use some of the more common terms ok 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 the 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 we'll 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 well 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 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 soo-min goes down and serotonin is partially responsible for feelings of satiation so this is why drugs can be problematic when you continually activate this dopaminergic 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 of morals or willpower and while people's choices are definitely strongly involved we now know that addiction has physiological 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 set in stone some evidence for the biological basis of drug dependence actually comes from animal models scientists can 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 compared 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 uh something bad happened when I took this drug but I don't really care I really need that reward and so what those kinds of studies show us is that addiction seems to take over a rational mind so 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 Pleasant pleasurable sensations are taken away from you