A recent study examines why it is hard to concentrate when you feel sick. This problem very likely reflects the effects of substances that are released by immune cells in the brain.
The research, published in Biological Psychiatry, describes how the immune cells, called inflammatory cytokines, help your body cope with infection.
During an infection, humans typically experience a set of physiological and psychological symptoms, including fever, confusion, decreased motivation, depression and anxiety that are accompanied by a slowing of movements.
These changes, collectively known as “sickness behavior,” are the body’s way of conserving energy during illness so that an effective immune response can be launched. This new study helps researchers further understand how cytokines communicate between the immune system and the brain to promote sickness behavior.
Brydon and colleagues utilized brain imaging to assess the impact of a typhoid vaccine, which prompts a low-grade immune response, on cognitive performance and brain activity in healthy young men. The scientists found that men with larger inflammatory cytokine responses to the vaccine had significantly slower reaction time responses during performance of a cognitive task and perturbed neural activity within a brain region facilitating movement known as the substantia nigra.
The substantia nigra is an important part of the motor system, releasing a chemical called dopamine to other brain regions to facilitate movement and motivate behavior.
The findings of this important study provide a valuable insight into the mechanisms by which infection and inflammation change the way we act and feel, specifically indicating
that chemical messengers released in the blood stream to combat infection can influence motivational centers in the brain leading to ‘psychomotor’ features of sickness.
John H. Krystal, M.D., Editor of Biological Psychiatry and affiliated with both Yale University School of Medicine and the VA Connecticut Healthcare System, comments on the value of this study: “The findings add to our growing knowledge of the intimate involvement of the brain, and by implication our patterns of thought and behavior, in the biology of the body.”
Dr. Lena Brydon, corresponding author on this article, agrees, adding that “understanding the link between the body’s immune defenses and the brain mechanisms responsible for sickness-related behavior may assist the development of novel interventions to control the depressive symptoms that accompany a wide range of inflammatory diseases.”
As the authors note, these mechanistic findings are critical to the development of interventions to control symptoms in inflammatory diseases as varied as obesity and cancer, or even neurodegenerative disorders such as Parkinson’s.