For the first time, dopamine regulation has been mapped in real time, deep inside the brains of three humans, revealing how the brain neurotransmitter plays an essential role in not just recognizing rewards but learning from mistakes.
Researchers from Wake Forest University School of Medicine (WFUSM) have unlocked crucial information about the brain’s decision-making mechanisms in a new study that could help us better understand how dopamine signaling differs in psychiatric and neurological disorders.
“Previously, research has shown that dopamine plays an important role in how animals learn from ‘rewarding’ (and possibly ‘punishing’) experiences,” said Dr Kenneth T. Kishida, associate professor of physiology and pharmacology and neurosurgery at WFUSM. “But little work has been done to directly assess what dopamine does on fast timescales in the human brain.
“This is the first study in humans to examine how dopamine encodes rewards and punishments and whether dopamine reflects an ‘optimal’ teaching signal that is used in today’s most advanced artificial intelligence research.”
For the study, the researchers used fast-scan cyclic voltammetry, paired with machine learning to measure dopamine levels in real time. Because this can only be done during invasive surgery, three patients scheduled to receive this kind of treatment – deep brain stimulation for essential tremor – were able to take part in the research.
A carbon fiber microelectrode was inserted deep into the brains of the participants to monitor dopamine in the striatum, the area of the brain involved in decision making, habit formation and reward.
They were then tasked with playing a simple computer game that had three stages requiring the participants to learn through experience to make choices that maximized rewards while minimizing punishments. The players were rewarded with real monetary prizes for making the correct decisions and lost money as a penalty for wrong moves. Dopamine was measured once every 100 milliseconds in each player, across all stages of the game.
And what they found was something quite unexpected: The dopamine pathway may be far more multifaceted and complex than we thought, playing as much a role in processing losses as it does wins. And these pathways operate on a different timescale.
“We found that dopamine not only plays a role in signaling both positive and negative experiences in the brain, but it seems to do so in a way that is optimal when trying to learn from those outcomes,” said Kishida. “What was also interesting, is that it seems like there may be independent pathways in the brain that separately engage the dopamine system for rewarding versus punishing experiences. Our results reveal a surprising result that these two pathways may encode rewarding and punishing experiences on slightly shifted timescales separated by only 200 to 400 milliseconds in time.”
The study indicates that dopamine is a key factor in how we learn from our experiences – good and bad – helping our brain adapt behaviors to make choices tied to positive outcomes.
“Traditionally, dopamine is often referred to as ‘the pleasure neurotransmitter,”’ Kishida said. “However, our work provides evidence that this is not the way to think about dopamine. Instead, dopamine is a crucial part of a sophisticated system that teaches our brain and guides our behavior. That dopamine is also involved in teaching our brain about punishing experiences is an important discovery and may provide new directions in research to help us better understand the mechanisms underlying depression, addiction, and related psychiatric and neurological disorders.”
The study was published in the journal Science Advances.
