Dopamine seems to be having a moment in the zeitgeist. You may have read about it in the news, seen viral social media posts about dopamine hacking, or listened to podcasts about how to harness what this molecule is doing in your brain to improve your mood and productivity. But recent neuroscientific research suggests that popular strategies for controlling dopamine are based on an overly narrow view of how it works.
Dopamine is one of the brain’s neurotransmitters: tiny molecules that act as messengers between neurons. It is known for its role in monitoring your reaction to rewards such as food, sex, money, or answering a question correctly. There are many types of dopamine neurons located in the uppermost region of the brainstem that produce and release dopamine throughout the brain. Whether the type of neuron affects the function of the dopamine it produces is an open question.
Recently published research reports a relationship between the type of neuron and the function of dopamine, and one type of dopamine neuron has an unexpected function that will likely reshape how scientists, doctors and the public understand this neurotransmitter.
Activation of dopamine neurons
Dopamine is famous for its role in reward processing, an idea that dates back at least 50 years. Dopamine neurons monitor the difference between the rewards you thought you would get from a behavior and the rewards you actually got. Neuroscientists call this difference a reward prediction error.
Dining at a restaurant that just opened and appears to be nothing special rewards prediction errors in action. If your meal is very good, this results in a positive reward prediction error and you will likely come back and order the same meal in the future. Each time you return, the reward prediction error reduces until it reaches zero when you fully expect a delicious dinner. But if your first meal was terrible, that results in a negative reward prediction error and you probably won’t return to the restaurant.
Dopamine neurons communicate reward prediction errors to the brain through their firing rate and patterns of dopamine release, which the brain uses for learning. They shoot in two ways.
Phasic activation refers to rapid bursts that cause a short-term spike in dopamine. This happens when you receive an unexpected reward or more rewards than expected, such as if your server offers you a free dessert or includes a nice note and smiley face on your check. Phasic activation encodes reward prediction errors.
In contrast, tonic activation describes the slow, steady activity of these neurons when there are no surprises; it is background activity interspersed with phasic explosions. Phasic fire is like the mountain peaks, while tonic fire is the valley floor between the peaks.
Functions of dopamine
Tracking information used to generate reward prediction errors isn’t all that dopamine does. I have followed with interest all the other dopamine work through my research measuring the brain areas where dopamine neurons are located in people.
About 15 years ago, reports began to emerge that dopamine neurons respond to adverse events – think brief discomforts such as a blast of air against the eyes, a mild electric shock, or a loss of money – something that scientists thought that dopamine didn’t do. These studies have shown that some dopamine neurons respond only to rewards while others respond to both rewards and negative experiences, leading to the hypothesis that there may be more than one dopamine system in the brain.
These studies were soon followed by experiments showing that there is more than one type of dopamine neuron. So far, researchers have identified seven distinct types of dopamine neurons by examining their genetic profiles.
A study published in August 2023 was the first to analyze dopamine function by neuron subtype. Researchers at Northwestern University’s Dombeck Lab looked at three types of dopamine neurons and found that two monitored rewards and aversive events while the third monitored movement, such as when the mice studied began to run faster.
Dopamine release
Recent media coverage on how to control the effects of dopamine is based only on the type of release that resembles highs and lows. When dopamine neurons fire in phasic steps, as they do to signal reward prediction errors, dopamine is released throughout the brain. These dopamine spikes occur very quickly because dopamine neurons can fire many times in less than a second.
There is another way that dopamine release occurs: sometimes it slowly increases until you get the desired reward. Researchers discovered this ramp pattern 10 years ago in a part of the brain called the striatum. The slope of the dopamine ramp tracks the value of a reward and the effort needed to obtain it. In other words, it encodes motivation.
The restaurant example can also illustrate what happens when dopamine release occurs in a gradual pattern. When you’ve ordered a meal that you know will be amazing and you’re waiting for it to arrive, your dopamine levels steadily increase. They reach a crescendo when the waiter places the plate on the table and you sink your teeth into the first bite.
How dopamine ramps occur is still uncertain, but this type of release is thought to underlie goal pursuit and learning. Future research into boosting dopamine will influence how scientists understand motivation and ultimately improve advice on how to optimally hack dopamine.
Dopamine(s) in disease and neurodiversity
Although dopamine is known for its involvement in drug addiction, neurodegenerative diseases, and neurodevelopmental conditions such as attention-deficit/hyperactivity disorder, recent research suggests that how scientists understand its involvement may soon need an update. . Of the seven subtypes of dopamine neurons known so far, researchers have characterized the function of only three.
There is already evidence that the discovery of dopamine diversity is updating scientific knowledge of diseases. Researchers in the recent paper identifying the relationship between the type and function of dopamine neurons point out that movement-focused dopamine neurons are known to be among the most affected in Parkinson’s disease, while two other types are not as affected. This difference could lead to more targeted treatment options.
Ongoing research to untangle dopamine diversity will likely continue to change and improve our understanding of disease and neurodiversity.
This article is republished from The Conversation, an independent, nonprofit news site dedicated to sharing ideas from academic experts. The Conversation is trusted news from experts, from an independent nonprofit. Try our free newsletters.
It was written by: Kimberlee D’Ardenne, Arizona State University.
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Kimberlee D’Ardenne currently receives funding from the National Institutes of Health (R21-MH130924-01) and has received other funding from the National Institutes of Health and the National Science Foundation in the past. She is also a member of the National Association of Science Writers and the Board of Editors in Life Sciences.