Dopamine takes a hit: how neuroscience is rethinking the ‘feel-good’ chemical

## Summary
The classic idea, known as the reward prediction error (RPE) hypothesis, is that bursts of dopamine in the brain link stimuli to rewards, helping to reinforce associations that fulfil a need for an animal or a person. This was a valuable rarity for researchers struggling to overlay simple theories onto the intense complexity of the brain. “Dopamine was the one field of neuroscience where we had a computational model that explained what the signal was and what it was computing,” says Mark Humphries, a neuroscientist at the University of Nottingham, UK. Wolfram Schultz, now at the University of Cambridge, UK, and his colleagues showed how the activity of dopamine neurons deep in the brain shifted as a monkey learnt to expect a reward. Article PubMed Google Scholar Download references Reprints and permissions Related Articles Untangling the connection between dopamine and ADHD How human brains got so big: our cells learned to handle the stress that comes with size Explaining dopamine through prediction errors and beyond Subjects Neuroscience Psychiatric disorders Lab life Latest on: Neuroscience Psychiatric disorders Lab life How the Pokémon franchise has helped to shape neuroscience Correspondence 17 MAR 26 China approves brain chip to treat paralysis — a world first News 16 MAR 26 Gut microbes affect cognition during ageing News & Views 11 MAR 26 Autism in older adults: the health system must recognize its effects Correspondence 17 MAR 26 My relationship with my PhD supervisor has become toxic — what do I do?

## Article Content
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Animation: Fabio Buonocore
When neuroscientists gather in the Spanish city of Seville in May for the annual Dopamine Society meeting, one discussion could be unusually lively. Session 31 will feature a debate between researchers who fundamentally disagree about the role dopamine has in the brain.
Untangling the connection between dopamine and ADHD
Dopamine is one of the most extensively studied neurotransmitters, chemicals that convey signals from cell to cell. It’s the one with the highest profile outside neuroscience: often known as the ‘pleasure chemical’, it’s depicted as the hit of reward that people get from recreational drugs or scrolling through social media.
That’s a gross simplification of what dopamine does; on that, researchers agree. But beyond that, where once there was a simple model that explained how dopamine works in the brain, now there are challenges that seek to amend the theory — or
even to overturn it
.
This could have implications not only for basic neuroscience, but also for clinicians trying to explain and treat conditions such as
attention deficit hyperactivity disorder (ADHD)
and
addiction
. If the model is wrong or needs modification, then so might some of the assumptions about what drives these disorders and the best way to treat them.
The classic idea, known as the reward prediction error (RPE) hypothesis, is that bursts of dopamine in the brain link stimuli to rewards, helping to reinforce associations that fulfil a need for an animal or a person. The model has dominated and guided research in the field for decades, offering a mathematical framework to interpret data from animal experiments, and it does a good job of explaining behaviour.
This was a valuable rarity for researchers struggling to overlay simple theories onto the intense complexity of the brain. “Dopamine was the one field of neuroscience where we had a computational model that explained what the signal was and what it was computing,” says Mark Humphries, a neuroscientist at the University of Nottingham, UK. People in the field knew that some of the assumptions involved in the RPE model were simplistic. But as a working understanding of part of the brain, it was seen as a major step forwards.
In the past few years, that primacy has begun to slip. About a decade ago, experimental techniques emerged that made it easier to monitor the release of dopamine from neurons in animal experiments. This threw the field wide open, with more laboratories able to gather and analyse data. And many of the data from these studies suggested that dopamine has functions in the brain that go way beyond reward, suggesting roles in cognitive functions such as attention, working memory and even social behaviours. Other studies showed that dopamine neurons can respond to new stimuli, threats and movement. The original model is no longer sufficient to explain all of this, Humphries says.
That leaves the field wrestling with a question, one that those who attend Session 31 in Seville will address: is this the end of the road for neuroscience’s most cherished model? Or is the idea, and the way it has been adapted by clinicians trying to understand ADHD, schizophrenia and addiction, now too big to fail? “I do think that the framework is insufficient,” says Kauê Costa, a neuroscientist at the University of Alabama at Birmingham. “But you know, if you aim at the king, you better not miss.”
Predicting reward
The idea of reward prediction has its roots in the famous twentieth-century experiments of Russian psychologist Ivan Pavlov. He established the idea of classical conditioning, showing that dogs learnt to associate environmental cues with the expectation of food. The principle inspired computer scientists trying to develop theories of machine learning in the 1960s, and was used in the 1990s to design neural networks.
Dopamine neurons (green) growing with other mature neurons (red) in a dish. DNA in the nucleus of each cell is shown in blue.
Credit: Jian Feng
In 1997, neuroscientists reclaimed the idea to explain data from a primate experiment
1
. Wolfram Schultz, now at the University of Cambridge, UK, and his colleagues showed how the activity of dopamine neurons deep in the brain shifted as a monkey learnt to expect a reward. At first, these neurons fired and released dopamine when the animal unexpectedly received a drop of fruit juice. Then the experimenters turned a light on before the juice arrived, and found that afterwards, the dopamine neurons were triggered by the light — the predictor of the reward — and not the juice. If the monkey expected but didn’t receive juice, there was a downward blip in the firing rate of dopamine neurons.
The RPE hypothesis says that dopamine signals allow the brain, over time, to make better estimates of where a reward — food, a mate, a safe place — might come from.
It’s a “shining highlight of computational neuroscience”, says Nathaniel Daw, a neuroscien

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## Expert Analysis

### Merits
- This was a valuable rarity for researchers struggling to overlay simple theories onto the intense complexity of the brain. “Dopamine was the one field of neuroscience where we had a computational model that explained what the signal was and what it was computing,” says Mark Humphries, a neuroscientist at the University of Nottingham, UK.
- The result can’t be explained by reward, and it faced significant headwinds from reviewers — and requests for further experiments, some designed to produce data linked to reward. “People were really mad about it,” she says. “It was like the rebuttal from hell.” One of the most direct challenges to the RPE crown comes from Vijay Mohan Namboodiri, a neuroscientist at the University of California, San Francisco, who has suggested an alternative model that is basically the reverse of RPE.

### Areas for Consideration
- Or is the idea, and the way it has been adapted by clinicians trying to understand ADHD, schizophrenia and addiction, now too big to fail? “I do think that the framework is insufficient,” says Kauê Costa, a neuroscientist at the University of Alabama at Birmingham. “But you know, if you aim at the king, you better not miss.” Predicting reward The idea of reward prediction has its roots in the famous twentieth-century experiments of Russian psychologist Ivan Pavlov.
- Dopamine responses can be tuned towards water when a songbird is thirsty, for example, but retune to prioritize singing when a potential mate is nearby — although how these neurons change their tuning is unclear.
- But she has found it difficult to publish papers that make that case.

### Implications
- Email Bluesky Facebook LinkedIn Reddit Whatsapp X Animation: Fabio Buonocore When neuroscientists gather in the Spanish city of Seville in May for the annual Dopamine Society meeting, one discussion could be unusually lively.
- Session 31 will feature a debate between researchers who fundamentally disagree about the role dopamine has in the brain.
- This could have implications not only for basic neuroscience, but also for clinicians trying to explain and treat conditions such as attention deficit hyperactivity disorder (ADHD) and addiction .
- If the model is wrong or needs modification, then so might some of the assumptions about what drives these disorders and the best way to treat them.

### Expert Commentary
This article covers dopamine, reward, neurons topics. Notable strengths include discussion of dopamine. Areas of concern are also raised. Readability: Flesch-Kincaid grade 0.0. Word count: 2397.