NEW YORK — Scientists are studying dopamine to understand decision-making and human behaviour.
Dopamine is a neurotransmitter produced in the brain that serves as a chemical messenger, facilitating communication between nerve cells in the brain and the body.
It is involved in functions such as movement, cognition and learning. While dopamine is most known for its association with positive emotions, scientists are also exploring its role in negative experiences.
The new study published in the journal Science Advances shows that dopamine release in the human brain plays a crucial role in encoding both reward and punishment prediction errors.
This means that dopamine is involved in the process of learning from both positive and negative experiences, allowing the brain to adjust and adapt its behaviour based on the outcomes of these experiences.
"Previously, research has shown that dopamine plays an important role in how animals learn from 'rewarding' (and possibly 'punishing') experiences. But, little work has been done to directly assess what dopamine does on fast timescales in the human brain," said Kenneth T. Kishida, Associate Professor of physiology and pharmacology and neurosurgery at Wake Forest University School of Medicine in the US.
"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," Kishida said.
For the study, the team utilised fast-scan cyclic voltammetry, an electrochemical technique, paired with machine learning, to detect and measure dopamine levels in real-time (i.e., 10 measurements per second).
However, this method is challenging and can only be performed during invasive procedures such as deep-brain stimulation (DBS) brain surgery.
DBS is commonly employed to treat conditions such as Parkinson's disease, essential tremor, obsessive-compulsive disorder and epilepsy.
The team inserted a carbon fibre microelectrode deep into the brain of three participants who were scheduled to receive DBS to treat essential tremor.
While the participants were awake in the operating room, they played a simple computer game. As they played the game, dopamine measurements were taken in the striatum, a part of the brain that is important for cognition, decision-making, and coordinated movements.
During the game, participants' choices were either rewarded or punished with real monetary gains or losses. The game was divided into three stages in which participants learned from positive or negative feedback to make choices that maximised rewards and minimised penalties.
Kishida said the study showed that dopamine not only plays a role in signalling 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.
"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," Kishida said.