In a new study, researchers at Wake Forest University School of Medicine (WFUSM) have revealed key information about the brain's decision-making mechanisms that could help us better understand how dopamine signaling differs in psychiatric and neurological diseases. The study is the first to map dopamine regulation deep in the brains of three people in real time, revealing the important role of the brain's neurotransmitters in recognizing rewards and learning from mistakes.
"Previous research has shown that dopamine plays an important role in how animals learn from 'reward' (and possibly 'punishment') experiences," said Kenneth T. Kishida, Ph.D., associate professor of physiology, pharmacology and neurosurgery at WFUSM. "But few have directly assessed dopamine's rapid effects in the human brain. This is the first study in humans of how dopamine encodes reward and punishment, and whether dopamine reflects the 'best' teaching signals used in today's most advanced artificial intelligence research."
In this study, researchers used fast-scan cyclic voltammetry paired with machine learning to measure dopamine levels in real time. Since this can only be done during an invasive procedure, three patients scheduled to receive this treatment - deep brain stimulation for essential tremor - were included in the study.
The researchers inserted a carbon fiber microelectrode deep into the participants' brains to monitor dopamine in the striatum, a region of the brain involved in decision-making, habit formation and reward.
They were then asked to play a simple computer game with three phases that required participants to learn through experience to make choices that maximized rewards while minimizing penalties. Players are rewarded with real money if they make the right decision; if they make the wrong decision, they lose money as a penalty. During various stages of the game, each participant's dopamine was measured every 100 milliseconds.
What they found was unexpected: The dopamine pathway may be much more numerous and complex than we thought, playing an equally important role in processing losing money as it does winning. And these pathways operate on different time scales.
"We found that dopamine not only plays a role in signaling positive and negative experiences in the brain, but it seems to do so in an optimal way when trying to learn from those outcomes," Kishida said. "What's also interesting is that there appear to be separate pathways in the brain , can engage the dopamine system in reward and punishment experiences separately. Our results revealed the surprising result that these two pathways may encode reward and punishment experiences on slightly different time scales, as little as 200 to 400 milliseconds apart."
This research shows that dopamine is a key factor in how we learn from good and bad experiences, helping our brains adjust behavior and make choices associated with positive outcomes.
"Traditionally, dopamine is often called the 'happy neurotransmitter,'" Kishida said. "However, our work provides evidence that this is not the case for dopamine. Instead, dopamine is an important component of a complex system that teaches our brains and guides our behavior. Dopamine is also involved in teaching our brains about punitive experiences, which is an important finding that may provide new research directions and help us better understand the mechanisms underlying depression, addiction, and related mental and neurological disorders."
The research was published in the journal Science Advances.