The brain’s dopamine system is what drives motivation. There is growing evidence that this system is directly affected by chronic, low-grade inflammation. The most recent finding suggests that this connection between dopamine, effort (motivation), and the inflammatory response is an adaptive mechanism to help the body conserve energy. A paper published in Trends in Cognitive Sciences explains the theoretical framework developed by scientists at Emory University to arrive at these findings.
Corresponding author Michael Treadway, an associate professor in Emory’s Department of Psychology, who studies the relationship between motivation and mental illness, said:
When your body is fighting an infection or healing a wound, your brain needs a mechanism to recalibrate your motivation to do other things so you don’t use up too much of your energy. We now have strong evidence suggesting that the immune system disrupts the dopamine system to help the brain perform this recalibration.
The authors even provided a computational method in the research paper to experimentally test their theory. Co-author Jessica Cooper, a post-doctoral fellow in Treadway’s lab, led the development of the computational model. Scientists can use the computational method to measure the effects of chronic inflammation on energy availability and effort-based decision-making. The approach may yield insights into how chronic, low-grade inflammation contributes to motivational impairments in some cases of depression, schizophrenia, and other mental health disorders.
Co-author Andrew Miller, William P. Timmie Professor of Psychiatry and Behavioral Sciences in Emory’s School of Medicine and the Winship Cancer Institute, is a leader in this field and is pioneering the development of immunotherapeutic strategies for the treatment of psychiatric disorders. Miller said:
If our theory is correct, then it could have a tremendous impact on treating cases of depression and other behavioral disorders that may be driven by inflammation. It would open up opportunities for the development of therapies that target energy utilization by immune cells, which would be something completely new in our field.
Inflammatory cytokines are signaling molecules used by the immune system. It has previously been shown that the cytokines impact the mesolimbic dopamine system. Then, additional research revealed more insights into how immune cells can shift their metabolic states differently from most other cells. The researchers of this new study built on all these previous findings to develop their theoretical framework.
The Theory
Back in our ancestral environments, life was rife with pathogens and predators. Therefore, our bodies likely adapted an immune system mechanism to help regulate the use of energy resources during times of acute stress. However, now in modern environments, many people are less physically active and may have low-grade inflammation due to factors such as chronic stress, obesity, metabolic syndrome, aging, and other factors. Under our current conditions, the same mechanism to conserve energy for the immune system could become maladaptive.
Studies have been conducted to prove this theory, and they have provided evidence of an association between an elevated immune system, reduced levels of dopamine and motivation, and some diagnoses of depression, schizophrenia, and other mental health disorders. The scientists are now using their computational method to test their theory in a clinical trial on depression.
Treadway concluded:
We’re not proposing that inflammation causes these disorders. The idea is that a subset of people with these disorders may have a particular sensitivity to the effects of the immune system and this sensitivity could contribute to the motivational impairments they are experiencing.
