字幕表 動画を再生する 英語字幕をプリント Part 4: Dopamine: The Molecule of Addiction Here's the normal pattern of dopamine release. It looks something like a roller coaster because in biology, what goes up must come down. It could be food, sex or even water when you're thirsty. So, let's say you're hungry. Dopamine starts rising. Then you think about a burger and it rises more. When the burger is sizzling, dopamine's going way up. It peaks right about at your first bite then you take some more bites then it starts to drop off, and finally drops back down to normal levels and you're full. This graph could also represent masturbating or having sex and the peak would be right about at orgasm. However, I really want to point out that the experience of orgasm is probably driven by other neurochemicals called Opiate, not dopamine. So, dopamine drives you toward orgasm but the feeling of orgasm arises from something else. The rise of dopamine levels could also represent anything new or novel, because dopamine loves novelty. A new car, a just released movie, the latest gadget, we're all hooked on dopamine. You can have a spike of dopamine just by ordering dessert even though you haven't finished what's on your plate. Dessert is something new. In fact, dopamine surging in your reward circuitry can override your feelings of what's called satiety or fullness regardless of what your rational brain may think about overeating or even watching porn. As with everything new, the thrill fades and dopamine levels drop. Now, back to the Coolidge Effect. So, dopamine is what is behind the Coolidge effect. If you look at our little graphs here, we have a female rat #1, female rat #2 and dopamine level. What's happening is that the reward circuitry of the male is squirting less and less dopamine in each copulation with female #1. And eventually, the male can no longer copulate, because there's not enough dopamine. Dopamine is behind libido. Then you dropped in female #2 and the male gets another squirt of dopamine which surges his libido and he goes back to work. This is what's behind the Coolidge effect and it's also why you click on to new videos while you're watching porn: to get another big squirt of dopamine with something novel. Ok. Let's give another nickname for dopamine. Let's call it the molecule of addiction. It's because changes in your brain that lead to addiction caused by changes in dopamine level. Cocaine, alcohol, nicotine, they all feel different but all of them flood the reward circuitry with dopamine. All addictive chemicals and activities raise dopamine levels. It's what makes them potentially addictive. Of course, you need continued use of the addictive substance or activity to cause physical changes that lead to addiction. Here's an odd thing. We've mentioned it before. Dopamine is released in response to expectations, rather than actual levels of pleasure. It's the drive to get it, it's the craving, but as I've mentioned, the actual pleasure of eating or orgasm is probably opioids. Those are morphine-like chemicals being released in the brain. Dopamine is wanting it, Opiates are liking it. Addictions are basically chasing after dopamine. So, what happen is addiction is wanting more but liking it less. Speaking of wanting and the power of the reward circuitry, here's an experiment. We have a rat and you see there's a wire and then this electrode that's actually going to the reward circuitry of the rat. And the rat has its little paw on lever and whenever he hits the lever it sends just enough electricity to the reward circuitry to stimulate it. Now, what will happen is this rat would just keep hitting the lever and hitting the lever thousands of times an hour until it drops. It won't stop to eat, sleep, have sex or even take care of the pups. It will give up everything just to press that lever. As we know, this behavior is not unlike some serious drug addicts. Here's another experiment. They take the same rat and then they have an electric grid between the lever and the rat so the rat has to feel painful shock in its little paws to go over to the lever and press it. Well, the rat will actually cross the bridge and endure the shock but if you take the rat and put it in electric grid between them and food, they will not cross the electric grid. They will not undergo shock to eat food, they would rather starve. Here's more experiment to show the power of dopamine in your reward circuitry. If you take rats and block their dopamine, they have absolutely no motivation. They're not even eat. They won't walk over to the food dish and they'll starve to death. But they still like food. If you drop food into their mouth, they eat it and show little rat's smiles, they just have no motivation to go get it. They lie around. They won't have sex either. The male rat shows no signs of libido. The key point is you need the right level of dopamine to function normally. It does lots of important jobs. Dopamine gives you that positive outlook, good attitude, keeps you motivated, keeps you happy. Incidentally, many psychological problems involved dopamine imbalances, including addictions. Donate and help us make Medical Education Universal, Free, State of the Art and Available to Every Human Being. For more such videos, join our Facebook group. Let's make Medical Education Universal, Free, State of the Art and Available to Every Human Being to enable the best medical facilities for everyone.