Which is powerful brain or money

Addiction - motivation to achieve bad goals

Eating, working, reproducing: without the brain's reward center, humans would probably do next to nothing. The mechanisms of motivation, however, have an unhealthy side effect: They are also the reason for our susceptibility to addiction.

Scientific supervision: Prof. Dr. Rainer Spanagel

Published: 02/12/2018

Level: medium

  • Addiction is a disorder of the brain's reward system.
  • Drugs work directly in the brain and lead to an increase in the release of dopamine.
  • Success at work, in computer games or gambling can also activate the reward system and make it addictive.

Every day we get up, have breakfast, and go to work. Why actually? Why are we doing anything at all? We could be lazy in the sun all day. Instead, we struggle, day after day. We eat, we drink, we procreate. What is it that drives us? The answer from brain research is simple but impressive: Because these activities in the brain activate our “pleasure center”, the nucleus accumbens.

This lump of nerve cells deep in our forebrain is the seat of the human reward system. It is stimulated by cells in the ventral tegmentum, a structure in the midbrain, with the messenger substance dopamine. If the messenger substance has docked on the receptor of the nucleus accumbens, it sends excitation potentials to other brain structures, which then trigger satisfaction and joy.

The reward system is activated by all sorts of stimuli: a three-course meal at an Italian restaurant, a hot date or sex, for example, cause a feeling of happiness, but also exercise or the smile of your own baby. In this way we are encouraged to repeat certain things over and over again. This mechanism probably evolved to motivate us to self-preserve.

The reward system is not unique to humans. Even the very simple nematode Caenorhabditis elegans, the favorite laboratory animal of many researchers, has a rudimentary motivation system. If scientists destroy only a handful of nerve cells that release dopamine in the worm, the animal no longer makes a detour for a bacterial meal. And if you teach your dog a new trick by giving him a bite to eat for every successful trick, you will also use the reward mechanisms of the nucleus accumbens.

The nucleus accumbens is the seat of the human reward system, which also plays a role in addictions because drugs intervene in the mechanisms of the reward system.

Drugs as a fatal abbreviation

However, humans have learned to shorten the path to neuronal reward: with cigarettes, alcohol, a pull on the crack pipe or a dose of heroin injected into their veins. The drugs intervene in the complex mechanisms of the pleasure center in different ways. Cocaine, for example, directly inhibits a dopamine transport system and thus leads to increased transmitter levels in the synaptic gap.

In the end, all drugs always have the same effect: the cells in the nucleus accumbens, which have dopamine receptors on their surface, are activated more strongly and for longer - and the brain signals: reward. Because drugs stimulate our pleasure center in this way up to ten times more intensely than food, for example, they are a powerful motivator.

Researchers demonstrated 50 years ago that this works in exactly the same way with animals: They gave rats the ability to inject drugs directly into the blood by pressing a lever. The rats also had two other levers in the cage. One led to the infusion of a saline solution, with a third they could “order” food. After a short time, the animals became addicted and, depending on the attempt, gave themselves more and more heroin, cocaine, and amphetamine.

At some point the addiction got so out of hand that the rats no longer even ate, and some died of malnutrition. Animals with damaged nucleus accumbens did not learn this addictive behavior. However, if only the cells were damaged that did not respond to dopamine anyway, the animals nonetheless developed an addiction - clear evidence that the messenger substance is involved in the addiction.

Drinking alcohol affects brain functions - and can be addictive. © dasGehirn.info

Addiction - a brain disease

Addiction also comes at a high price at the neural level. The rest of the brain subordinates itself to the changed reward system and the addict is only concerned with how to get the next dose of his drug. Friends, family and careers take a back seat. At the same time, there is a fatal side effect: the dose often has to be increased further in order to achieve the same effect. The reason: The reward system becomes dull and has to be shaken up again with ever larger amounts of the respective substance. The addict gets into a destructive spiral that pulls him down like a vortex.

The close connection between drugs and the reward system can also be demonstrated with imaging methods: in a brain scanner, the nucleus accumbens of a cocaine addict lights up when the drug is offered to him. Or when he sees a video of someone using cocaine.

But drugs are by no means the only addictive pathogens. Compulsive gamblers who are shown pictures of a one-armed bandit show the same activation in the nucleus accumbens. And work, sports, computer games and the Internet are also addictive. Because what can trigger a reward in the brain always harbors the risk of making people dependent. That is the fatal side effect of motivation: it is actually vital. But if people learn to stimulate the motivational center more and more, they can become dependent - with long-term consequences for the whole brain.

Researchers now know that the nucleus accumbens is not the only brain region that plays a role in addiction: the amygdala is important for the emotional coloring of the memory, the hippocampus for the fact that a memory is stored at all. In these regions, too, drug addicts show changes. This explains why, even after years of being “clean”, they can relapse under stress or a simple reminder.

"Addiction is a brain disease," says Alan Leshner, longtime head of the US State Institute for Drug Abuse. But like so many diseases, addiction has helped researchers better understand vital mechanisms - in this case, motivation and the question of why we make an effort to do a variety of things.

Publication: on 08/15/2011
Update: on February 12th, 2018