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Here you are again, stuck at home with a nasty cold. You don’t feel like doing anything and just want to lie on the couch all day. This happens because your immune system affects your brain, and thus how you feel and behave. How does that work?
Less dopamine = less motivation
While your body is busy battling the pathogens, your immune system produces cytokines; these are anti-inflammatory substances which travel throughout your whole body. They also end up in your brain, where they mostly influence dopamine. Dopamine is an important neurotransmitter, a particle for communication in the brain, that is involved in motivation and seeking of reward. Dopamine helps you to achieve goals. It gives you the drive to make your favourite recipe or go to football practice.
If there’s an inflammation in the body, the amount of dopamine decreases. This is why you feel tired and apathetic when you’re ill. This mechanism has a logical evolutionary explanation: it makes sure you rest and save your energy, which you need to beat whatever’s making you sick.
Depression is linked to inflammation
In case of illness, it is useful that your immune system can influence your brain. But sometimes the immune system has an effect that doesn’t really make sense, evolutionarily speaking. An important example of this is the role of the immune system in depression. A large proportion of depressed people have low-grade inflammation. This is not the brief-yet-intense inflammation you get from cold, but rather a longer low-intensity activation of the immune system. Low-grade inflammation could have multiple causes, like prolonged stress, an unhealthy lifestyle, or a genetic disposition. This low-grade inflammation is often correlated with the symptoms: the worse the inflammation, the stronger the depressive symptoms. We see this because even low-grade inflammation causes a reduction in dopamine, resulting in fatigue and reduced motivation.
Fortunately, this relation between the immune system and the brain also creates opportunities for treatment. In recent years, research has studied the effect of anti-inflammatory medication on depression, and with success: it seems to reduce symptoms in people with depression.
Overweight, inflammation, and the brain?
Other conditions that involve inflammation may also affect the brain. For example, people that have overweight often have mild chronic inflammation, caused by a certain type of fat tissue. This inflammation might also affect dopamine, and thereby motivation. These changes to dopamine might be one factor that contributes to the difficultly of maintaining a change of life style or diet. At the Donders Institute we are currently studying the influence of the immune system on the brain in people with overweight. In this way, we hope to further unravel the relationship between the brain and the immune system!
Participate in research into the influence of the immune system on the brain?
At the Donders Institute we’re looking for female participants from 18 to 55 years old. For more information go to the website: https://www.ru.nl/donders/projects/flair-studie/