When people get sick, they often also feel tired, which can be as troublesome as their disease. A team of researchers has learned more about this connection. Reporting in the journal NeuroImage, they have shown that inflammation, which is a natural biological response to illness, can have a detrimental impact on the brain's state of alertness and the ability to maintain it.
"Scientists have long suspected a link between inflammation and cognition, but it is very difficult to be clear about the cause and effect," said the co-senior author of the study Dr. Ali Mazaheri, of the University of Birmingham's Centre for Human Brain Health. "For example, people living with a medical condition or being very overweight might complain of cognitive impairment, but it's hard to tell if that's due to the inflammation associated with these conditions or if there are other reasons. Our research has identified a specific critical process within the brain that is clearly affected when inflammation is present."
In this study, the scientists zeroed in on a part of the brain that functions in visual attention. Twenty young men volunteered to get a vaccine for salmonella typhoid, which results in temporary inflammation but doesn't have many other side effects. On a different day, the volunteers were also given a water injection as a control. The cognitive responses of the study participants were assessed by showing them images on a computer a few hours after they got the vaccine or the placebo, and brain activity was measured as they took the attention test. Blood was also taken to measure their inflammation levels.
Separate attention processes that involve different regions of the brain were assessed in this study. Alerting involves obtaining and maintaining an alert state, orienting is related to choosing and prioritizing sensory information, and executive control can resolve the choice of what to pay attention to if there is conflicting sensory information. The researchers determined that inflammation had a specific impact on staying alert, and the other processes were unaffected.
"These results show quite clearly that there's a very specific part of the brain network that's affected by inflammation," noted Dr. Mazaheri. "This could explain 'brain fog'."
"This research finding is [a] major step forward in understanding the links between physical, cognitive, and mental health and tells us that even the mildest of illnesses may reduce alertness," said co-senior study author Professor Jane Raymond of the University's Centre for Human Brain Health.
"Getting a better understanding of the relationships between inflammation and brain function will help us investigate other ways to treat some of these conditions. For example, further research might show that patients with conditions associated with chronic inflammation, such as obesity, kidney disease or Alzheimer's, could benefit from taking anti-inflammatory drugs to help preserve or improve cognitive function," added the first author of the study, Dr. Leonie Balter. "Furthermore, subtle changes in brain function may be used as an early marker cognitive deterioration in patients with inflammatory diseases."
The scientists want to analyze how inflammation can influence other functions of the brain, like memory, next.
Inflammation and an overactive immune system have also been connected to chronic fatigue syndrome. Learn more from the video above. Inflammation is also related to a wide variety of different disorders, which is discussed in the video below.
Sources: AAAS/Eurekalert! via University of Birmingham, NeuroImage