Is It Rewarding? How Dopamine Affects Short-Term & Long-Term Decisions

Picture this – an Olympic athlete training for the delayed Summer Tokyo Olympics versus an overworked student working from home and snacking. For the athlete, they feel the pain of exertion as they exercise daily and continue testing their limits. In the case of the student, snacking on junk food is a reprieve from stressful cramming before a virtual exam. Between the two, you might find one more relatable than the other. The Olympic athlete is, of course, imagining their future success –overcoming short-term pain by focusing on winning a future gold medal. The student may be ignoring long-term health consequences, mainly because the short-term reward is too tempting.  The fear of quarantine weight gain, or “COVID curves” as some say, can be tomorrow’s problem after just one more chocolate!

Between an Olympic athlete and your average stressed out student, could different brain functions underlie their decision-making processes?

Dopamine is the crucial mechanism at work within this decision-making. Despite its popularity in psychological news, dopamine is not just involved in making you feel happy. It is a chemical messenger that helps the brain interpret rewards, punishments, movement, and can even influence decision-making and memory. But how is dopamine able to impact such a diverse set of behaviours? This question is of interest to Trainees from the Cognitive Developmental Neuroimaging Lab (CDNL) in the Brain and Mind Institute at Western University.      

A side-by-side comparison of two women, one getting ready for a run and the other lying down on a couch. We might relate to one of these women more, but dopamine functioning has significantly affected both of their decision-making.

Ph.D. Candidates Nikki Kamkar and Masood Rezaei have taken on the task of modelling how dopamine impacts learning in humans. Their overlapping goals aim to fill in the gaps pertaining to dopamine function and its effects on reward-based learning and decision-making.

In 2017, Kamkar and her colleagues investigated factors that can cause deficits in normal dopamine functioning and impact the brain’s reward system. For decision-making, the reward system is an integral part of providing a reason for us to want to accomplish a task. The network of brain regions that make up our reward system all rely on dopamine in order to communicate with each other. When you are given a reward, dopamine is released and sends associated positive signals to your reward system.

However, outside of rewards, the amount of dopamine that stays active in your brain is also critical. Normal dopamine levels affect how much dopamine is released for signalling rewards. In this way, increased dopamine release influences how enjoyable rewards are perceived to be.

Unfortunately, more dopamine is not necessarily a good thing. Increased dopamine release has been strongly linked with attention deficit hyperactivity disorder (ADHD) in children, favouring impulsive decision-making. 

It is this aspect of dopamine functioning that Kamkar wanted to delve deeper into; especially how normal dopamine levels can be impaired. After examining results from earlier research, she settled on studying childhood adversity as a key negative factor for dopamine. 

According to previous experiments, adversity affects the development of the reward system. Childhood is a sensitive period for the brain, which is why a reward system that expects difficulty will overreact when given a rare positive reward. The reward system thereby releases a higher amount of dopamine per reward and keeps more dopamine active in the brain. Subsequently, childhood adversity often predicts elevated dopamine levels.

Across two studies, Kamkar and colleagues decided to further examine these effects of elevated dopamine on decision-making behaviour in 9-12-year-old children. More specifically, by observing how early life adversity can impair reward prioritization and impulsive decision-making. For both experiments, adversity was measured by parents describing the number of emotionally charged events experienced by their child (e.g., changing schools, moving to a new neighbourhood, loss of a pet, etc.) and the severity of their child’s responses to them.

Kamkar tested what types of decisions adversity elicits in children using a combination of neuroimaging and decision-making tasks. They found that high levels of adversity significantly predicted children over-prioritizing rewards (making rewards more tempting) and discounting delayed rewards (choosing a small immediate monetary reward over a large reward later). 

That being said, these results do not explain how dopamine affects reward-based decision-making in the average person who has minimal experiences of childhood adversity.

To fill in this knowledge gap, Rezaei plans to take a different approach in a future research project and better establish the relationship between elevated dopamine levels and decision-making. Starting in 2019, he began investigating the effects of the drug Levodopa (L-DOPA); a dopamine increasing medication typically prescribed to supplement low levels of dopamine in Parkinson’s disease.     

For the purposes of Rezaei’s research, L-DOPA provides a safe means of examining the effects of temporarily increased dopamine in research participants who otherwise have normal levels of dopamine. 

Accordingly, Rezaei intends to explore how increased dopamine affects two types of behaviours: goal-directed (actions that pursue a direct reward) and habitual (automatic actions that respond to immediate or familiar rewards). He plans to administer L-DOPA to normal adults, observe any changes in these two types of behaviours, and see how increased dopamine affects brain activity during neuroimaging. 

With in-person research participation returning to campus, there is so much more we will continue to learn about dopamine levels and short-term versus long-term decision-making.

For the time being, Rezaei states that current research points towards dopamine being “…especially important for balancing actions based on short-term reward and long-term consequences”.

As for what this entails for our athlete and student? You may not have mastery over how your brain releases dopamine, but you do have control over how you perceive rewards. Rezaei explains that habitual behaviours are motivated by rewards initially but do not require the same reward over time. Repeating behavioural patterns over and over again can help train them into routine habits. Likewise, a delayed long-term goal is motivating when a sufficient reward is associated with it. 

For an Olympic athlete, winning a gold medal is inspirational enough to devote themselves to intense training. And for any students also trying to ditch junk food – try to slowly change snacking habits into isolation breaks to buy your favourite fruits from the farmers market this summer!