Dopamine is a neutrotransmitter with rock star status. And although it deserves to be well known for all the important work it does in our brain, much of the facts tend to get lost in rumors that come with this status. This is a true story of dopamine and how it came to be a rock star.
Dopamine has turned into a popular adjective and catches people’s attention. In recent years, it is often used to give weight to, for example, new lifestyle-changing hypes and make people believe they are scientifically sound: dopamine fasting, dopamine dressing, dopamine dieting. Much to the dismay of neuroscientists who study what dopamine does in the brain, and how it can help us understand human behavior and disorders better. More importantly, the exploitation of dopamine is problematic. People are being convinced to change their lifestyle, sometimes dramatically, without good grounds. Another big problem is that misrepresenting of scientific findings, whether it is intentional or out of not knowing better, eventually leads to confusion and mistrust in science.
The story of dopamine is a good example of what happens when scientific findings are pulled out of context and start living a life of their own. As rumors that travel to all corners of the world. What happens is similar to a simple game of Chinese Whisper, where you whisper a message into someone’s ear and they have to pass it on to the person next to them in the same way. With every intermediate stop, the message deviates further from the original, which can end up in a disturbingly different message at the end.
When researchers discovered a link between dopamine and the experience of pleasure (Wise, 1980), the news also travelled outside of science. It was so exciting that it travelled far and wide. In fact, the message seems to be travelling still, with the concoction of these new life-changing interventions that are either supposed to miraculously improve life by stimulating release of the ‘pleasure’ or ‘happiness’ hormone in the brain, or by its exact opposite, to prevent its release. Isn’t that confusing? Yes! Even though the scientific community, including the researchers who initially found the link with pleasure, have moved on and accept new evidence that clearly shows that dopamine is in fact not responsible for our experience of pleasure or happiness. That makes the true story of dopamine a beautiful example of how science and its self-correcting principle functions.
The true (and long) story
How it all began
Dopamine started out as an underdog (like a real rock star). In the brain, it was initially thought of as a by-product of the neurotransmitter noradrenaline and without a function of its own. Only in the 1950s, dopamine was shown to function as a neurotransmitter itself, giving it a crucial role in the passing on of signals from one neuron to the next. This was a huge change in status.
In the same period, other researchers discovered a part of the brain that was involved in experiencing reward – Sex, Drugs (& Rock ‘n Roll) – and interpreted it as the brain’s pleasure center (Olds & Milner, 1954; Olds, 1956). They found out that rats would keep stimulating themselves by continuously pressing a simple lever that activated those brain regions by means of an implanted electrode. As if they couldn’t get enough of it. The remarkable thing is that rats even started to neglect their basic needs, similar to what is seen in addiction. It wasn’t until 1980 until a link between this particular part of the brain and dopamine was made (Wise, 1980).
But let’s go back in time. First, dopamine was thought to be involved in control of our movements. A lack of it could really shake things up. Losing a substantial amount of the neurons that produce dopamine turned out to be characteristic for Parkinson’s Patients. These patients typically suffer from movement-related symptoms such as trembling hands and trouble initiating movements. A medication that increases dopamine production in the brain, found in the 1960s, still is one of the most common treatments for Parkinson’s disease. With this breakthrough, dopamine gained the interest of many more scientists.
The many ways of dopamine
New tools were developed. With these tools it was possible to observe dopamine and its “habitat” in much more detail. Scientists started to map the paths that dopamine takes in the brain. Guess what? The “pleasure center”, or rather the much larger reward system as it turned out later, was on its paths. Researchers also learned about receptors that dopamine can bind to. As some kind of key to open doors, so that signals can travel from one neuron to the next and affect communication in the brain.
The development of medication that could bind to dopamine receptors led to another turning point in dopamine research in the 1970s. An important class of medication for the scientific discovery of dopamine were neuroleptics that mainly block specific receptors. These medications were shown to have antipsychotic action and could be used in scientific research to investigate the causal role of dopamine in a particular pathway in the brain. It became clear that dopamine deficits could not only result in problems with control of movement, but also symptoms of cognitive and motivational disorders, such as schizophrenia, attention-deficit-hyperactivity disorder (ADHD), and importantly addiction.
Addiction is an interesting example to illustrate the importance of nuance in the story of dopamine. Although the experience of pleasure and the receiving of reward often occur together, and the experience of pleasure may motivate your next decision (“chocolate makes me feel good, so I’ll eat it again”), the two are not necessarily the same. This is what was clarified in later research. Researchers proposed a distinction between liking (pleasure) and wanting (motivation), where it is not liking but wanting that relies on dopamine (Robinson & Berridge, 1993). Addictive substances may initially result in pleasure and use can then be driven by liking. However, with prolonged use and development of addiction, someone no longer experiences the same pleasure (liking) while using the substance, but still is very motivated to get it (wanting).
A diverse repertoire
Now, with the existence of different paths and receptor mechanisms, it is not surprising that dopamine has a diverse repertoire. Much like Freddy Mercury with his band Queen, whose music cannot be captured by one single style.
In the past decades, dopamine research really took off and branched out. It was shown to be involved in many important functions – as a Swiss army knife – in both health and disease. Dopamine is key to working memory, processing of all sorts of reward (the taste of chocolate) and of cues that we have learned to associate with reward (hearing someone open the chocolate drawer). It is also involved in learning from rewards and punishments, the amount of effort we are willing to put in to achieve a certain goal (to go buy chocolate if it’s empty), and many more nuances of these processes.
Some researchers attempt to unify seemingly distinct functions of dopamine. Motivation is a key concept that comes back in dopamine theory time and again. A promising suggestion is that an important role of dopamine is to modulate the process of what decision are worth to take and what not, given limited resources (Berke, 2018). Even movement deficits, such as, difficulty initiating movements, could be explained by dopamine’s role in deciding to move or not.
Is there an end to this story?
At this point your head may spin from all the different processes that dopamine is involved in. And what does it even mean that the term motivation comes back all the time? Can we now say that dopamine is motivation instead of pleasure?
Well, it’s complicated. Welcome to science. In our current understanding, it indeed seems better to say that dopamine is critically involved in motivation. But we should think (and test) again (and again, and again… Don’t Stop Me Now!) before the same mistake is made and new rumors start living a life of their own. Instead of rumors, we need to spread knowledge in nuanced scientific “stories” and we need to teach how to deal well with their open-ended nature. We need to do justice to the rock star that dopamine really is.
Berridge, K. C. & Kringelbach, M. L. Pleasure systems in the brain. Neuron 86, 646–664 (2015). https://doi.org/10.1016/j.neuron.2015.02.018
Björklund, A. & Dunnett, S. B. Fifty years of dopamine research. Trends Neurosci. 30, 185–187 (2007). https://doi.org/10.1016/j.tins.2007.03.004
Cools, R. Role of dopamine in the motivational and cognitive control of behavior. The Neuroscientist 14, 381–395 (2008). https://doi.org/10.1177/1073858408317009
Robinson, T. E. & Berridge, K. C. The neural basis of drug craving: an incentive-sensitization theory of addiction. Brain Res. Rev. 18, 247–291 (1993). https://doi.org/10.1016/0165-0173(93)90013-P
An interesting line of research that builds on the work by Olds & Milner is very well captured in this comic.
The German version of this blog has previously been published on SciLogs Thinky & Brain.