Cutting-edge technology allows MSU psychologists to reveal new ways in which dopamine affects decision-making

March 30, 2021 - Liz Schondelmayer

Dopamine is a neurotransmitter in the brain that is known for making us feel good. But besides helping us feel happy, it also plays a big role in our ability to make decisions and put effort into certain tasks, especially when the result is a reward that we want. 

Recent research from Dr. Alexander Johnson (pictured left), an associate professor of Psychology in the Michigan State University College of Social Science, explored this connection between dopamine and decision-making, finding that dopamine stimulation can interrupt how we choose to put effort into reward-based tasks. 

For this study, Dr. Johnson and his research team, including PhD candidate Benjamin Fry, and undergraduate research assistants Nathan Pence and Andrew McLockin, worked with mice. The team provided the mice with two sugar solutions, one slightly better-tasting yet more difficult to access than the other, and directly altered some of the mice's dopamine levels to see how the mice would respond when choosing between the rewards.

"We used a revolutionary neuroscience technique called optogenetics, which allows us to directly and selectively alter dopamine cells in the brain with a light-sensitive ion channel," explained Dr. Johnson. "The cells are unaffected when no light is on, but are activated when light is applied, allowing dopamine to stimulate the brain."

The team found that the mice with unaltered dopamine levels were willing to work hard to reach the better reward. Surprisingly, however, when the researchers stimulated the dopamine release, mice became less willing to work for the better tasting solution.

"While the control mice were willing to work extremely hard to access the better-tasting solution, the stimulated mice were much more content with the lower value, more immediately accessible outcome," explained Dr. Johnson. "These findings suggest that elevated dopamine levels may impair cost-benefit decision-making."

Moreover, the team found that on the day following the dopamine stimulation, the mice were willing to work even harder for the better-tasting solution. This long-term effect suggests that the previous day's stimulation of dopamine led the mice to be less interested in the rewards, which they compensated for by working even harder for the better reward available.

"This pattern of findings is difficult to explain within the context of what we typically think dopamine does," observed Dr. Johnson. "Our optogenetic technology has revealed something interesting by revealing that our everyday decisions and behavior are guided by choices based on value versus effort trade-offs. 

Despite obvious differences between a mouse brain and a human brain, there is enough in common for observations of mice behavior to translate to our understanding of our own behavior.

"Even though the human brain is far more evolutionarily-adapted, many of our lower-level brain systems - including the dopamine system - are similar to those of many other mammals, including mice!" said Dr. Johnson. "Reward-based decision-making is something that both animals and humans do everyday when interacting with and navigating their environments." 

This research has important implications for disorders such as depression and schizophrenia, which typically involve disruptions in reward-based decision making. Moving forward, the research team is hoping to further their understanding of dopamine by identifying the circuit path in the brain that the dopamine cells follow.

Find the full research article here.