The physical and mental health benefits of exercise are widely known, but finding the motivation to exercise can be a challenge. The study authors said a look inside the brain may shed light on how people can be encouraged to maintain healthy exercise habits. More specifically, the dopamine reward system may play a role in motivating people to exercise, and the study authors proposed that regular exercise could alter the brain’s reward response.
“My background is in eating disorder research, and these people tend to exercise very high. Before exploring the effects of exercise in this population, I wanted to study the relationship between exercise and food processing. brain reward, specifically dopamine-related reward processing,” said study author Guido KW Frank of the University of California, San Diego.
The researchers examined brain activity during a reward prediction error (RPE) task. An RPE is when a person receives an outcome of an event that is different than expected, causing dopamine neurons to send a signal. This unexpected outcome can be positive, such as receiving an expected reward, or negative, such as being unexpectedly deprived of a reward. RPE is thought to reflect motivational salience, a cognitive process that drives a person’s behavior toward a positive outcome. The researchers speculated that people who exercise more frequently might show a stronger response in the dopamine system.
“The type of response of the reward system that we focus on is responding to the receipt of unexpected stimuli: it could be called excitement for receiving a reward unexpectedly, or unexpected omission of stimuli or disappointment for not receiving a reward that was expected” , Frank told PsyPost. “The stimuli we use are sucrose or water taste stimuli.”
A group of 111 healthy women participated in a task that elicited the dopamine-related RPE response. The task involved a classic sucrose taste conditioning paradigm where participants learned to expect or not to expect a sucrose reward. Throughout the task, functional magnetic resonance imaging (fMRI) was used to measure the participants’ brain activity. In addition, the women reported the amount of aerobic exercise they do each week.
The researchers then analyzed the fMRI data, focusing on brain responses when the participants unexpectedly received a sucrose reward, did not receive it unexpectedly, or received it as expected. For all three conditions, increased exercise was associated with a stronger response in the right medial orbitofrontal cortex (OFC). But after correcting for multiple comparisons, this increased activity was only significant during the unexpected reception condition.
“A greater amount of cardiovascular/aerobic exercise was associated with a higher brain response (orbitofrontal cortex, an area between the eyes that is important for the assessment of rewards) when participants received the sugar stimulus unexpectedly, but did not affect the response to the unexpected omission of the stimulus or disappointment,” Frank explained. “We think that increased exercise can change your brain, and getting a reward unexpectedly is more enjoyable.”
In particular, the right medial OFC is involved in goal-directed decision-making and the calculation of reward value. The results may suggest that exercise strengthens this circuit, driving higher brain activity in the OFC. Alternatively, it could be that higher activity in the OFC reinforces exercise participation.
“Therefore, it is possible that individuals who engage in more aerobic activity may be intrinsically more sensitive to salient stimuli and especially to receiving stimuli,” the researchers wrote, “or alternatively, participation in aerobic exercise has modulated brain activity and dopamine signaling, which can reinforce and functionally maintain exercise behavior reflexively.” The authors point out that both of these explanations could be true.
Overall, the results suggest a link between aerobic exercise and the brain’s response to an unexpected reward. “It is possible that exercise may in particular enhance the ability to value or enjoy stimuli or experiences, which could be important for intervening in psychiatric disorders,” the authors said, adding that an “altered relevance response brain damage is characteristic of many psychiatric illnesses.” ” If exercise is found to improve the importance of motivation, this could reveal potential treatment options for affected individuals.
Among the limitations, the study was cross-sectional and future longitudinal studies will be necessary to draw more robust conclusions from the data. In addition, participants self-reported their exercise levels, and it is unclear whether the results reflect the effects of general activity level or actual aerobic exercise.
“We can’t be sure exactly which neurotransmitters are involved, and a larger study sample might have indicated that higher cardiovascular exercise also protects against disappointment,” Frank said. “Cardiovascular exercise may help you be happier by being able to enjoy things more and be less disappointed when something doesn’t work out the way you thought it would.”
“It is important that this was a study in healthy controls and that their amount of exercise was within normal limits,” he added. “Excessive exercise can prevent a healthy life and will not have a positive effect on your well-being because you may lose a lot of weight and/or develop an eating disorder.”
The study, “Associations between aerobic exercise and dopamine-related reward processing: Informing a human exercise participation model,” was written by Sasha Gorrell, Megan E. Shott, and Guido KW Frank .