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Current time:0:00Total duration:5:33

Video transcript

so in the previous video we talked about the reward circuit in the brain at sort of a broad level and now what we're going to talk about is how that works at a lower level at the neuron level so that we can discuss issues like tolerance addiction and withdrawal now behaviorally tolerance just means that you get used to a drug so that you need more of it in order to achieve the same effect so let's look at how that works inside your brain so let's take a look at what's happening with the neurons here so imagine if this is the axon of one neuron and the dendrite of another and then in here is the synapse all right so then we have these neurons they're coming from the VTA and they're sending dopamine so imagine that you've just taken some cocaine so all of this dopamine is flowing pleasure signals gone crazy pretty happy okay so tons of dopamine and what normally happens here is that the postsynaptic neuron has receptors for certain neurotransmitters such as dopamine it has these little spots for the dopamine to come and it gets taken up and it sends the signal on and that's how you experience the forea it's that stimulation of the neurons along that pathway now in a normal situation if your stimulus had been say a hug or something then then you would still experience this feeling of pleasure but then your brain chemistry would go back to normal after a second it would balance itself out with drugs long term stimulation can actually alter your brain chemistry so what happens when your brain is just constantly over stimulated with dopamine it's too much work and it tries to balance it out believe it or not you don't always want to be super we're happy released your brain doesn't so what happens after a while as it says okay I need to calm down I'm going to shut down some of these receptors so that way the same amount of drugs won't cause me to be so overstimulated I won't get as much of a high from the same amount of drugs so when that happens that is called tolerance because you have built up a tolerance to the same amount of drugs and it doesn't have the same effect anymore now with drugs like cocaine in particular this can cause a problem because you started to develop a dependence on it usually talk about a combination of sort of emotional dependence of feeling like you need the drug as well as a physical dependence you actually experience negative physical symptoms without it so once you've built up this tolerance and you still want to feel that high you end up taking more cocaine to get the same feeling and so then you just have to keep kind of increasing your dosage over time okay so that's what happens if you have just free and steady access to drugs you just keep increasing your dosage up to the point on the other hand you might not always have access to the drug and if you go through a period of not having it then that is when you experience withdrawal symptoms so remember now your body has gotten accustomed to this very high level of dopamine and it's gotten accustomed maybe to not producing it on its own but relying on the drug once you start taking cocaine I mean things like chocolate and hugs won't make you quite as happy as the cocaine does you to end up seeking out this cocaine and the pleasurable sensations it can produce in the place of other types of stimulation so then without it you don't have the same level of dopamine your body's not producing it on its own so you tend to feel depressed and feel highly anxious and the specific symptoms will vary by type of drug sometimes you'll sweat have headaches generally anxiety and depression are pretty common and when those are extreme enough you'll really do whatever it takes to make yourself feel happy again the thing is though you're not even going for the euphoria anymore you're going for normal once you've built up this tolerance you need the drug to feel normal again not even euphoric and this is usually a sign that you are addicted to the drug which means that you feel a need to keep taking it the good news is that even though withdrawal is miserable just like your brain can get used to the presence of drugs it can get used to the absence of drugs again so it's some time and effort even if the drugs have caused some irreparable damage to other parts of your brain you can get your reward system back to functioning at a more normal level