Scientists from the University of Birmingham, in collaboration with the University of Amsterdam, have found a possible explanation for the mental sluggishness that is often associated with an illness.
It is estimated that 12 million British citizens suffer from a chronic illness and many of them report severe mental fatigue, which they call "sluggishness" or "brain fog". This condition is often as debilitating as the disease itself.
A team from the University Center for Human Brain Health examined the connection between this mental fog and inflammation - the body's response to disease. In a study published in Neuroimage, they show that inflammation has a particularly negative effect on the willingness of the brain to reach and maintain an alarm state.
Dr. Ali Mazaheri and Professor Jane Raymond from the University's Center for Human Brain Health are the lead authors of the study. Dr. Mazaheri says: "Scientists have long suspected an association between inflammation and cognition, but it is very difficult to determine the cause and effect. For example, people who are ill or overweight may complain of cognitive impairment, but it is difficult to say if this is due to the inflammation associated with these conditions or if there are other reasons. "
"Our research has identified a specific critical process in the brain that is clearly affected when there is inflammation."
The study specifically focused on an area of the brain that is responsible for visual attention. A group of 20 young male volunteers participated and received a salmonella typhoid vaccine that causes transient inflammation but few other side effects. They were tested for simple images on a computer screen a few hours after being injected for cognitive responses to measure their ability to control attention. Brain activity was measured while attention tests were being performed.
Another day, either before or after, they were injected with water (a placebo) and did the same attention tests. They did not know which injection they had received on each test day. Their inflammatory condition was measured by analyzing the blood taken daily.
The tests used in the study assessed three separate attention processes, each involving different parts of the brain. These processes are: "Alert", which means reaching and maintaining an alarm condition; "Orientation", in which useful sensory information is selected and prioritized; and "executive control", which is used to clarify what to look for when the available information conflicts.
The results showed that inflammation specifically affected brain activity related to maintaining alertness, while the other attention processes did not appear to be affected by the inflammation.
"These results show quite clearly that there is a very specific part of the brain network that is affected by inflammation," says Dr. Mazaheri. "This could explain 'brain fog'."
Professor Raymond says: "These research results are an important step forward in understanding the links between physical, cognitive, and mental health, and they tell us that even the mildest diseases can reduce alertness."
Dr. Leonie Balter, the first author of the study to complete her PhD, concluded: "A better understanding of the relationship between inflammation and brain function will help us explore other ways to treat some of these disorders. For example Further research could show that patients with chronic inflammation such as obesity, kidney disease or Alzheimer's can benefit from anti-inflammatory drugs to maintain or improve cognitive function. "
"In addition, subtle changes in brain function can be used as a cognitive deterioration in the early marker in patients with inflammatory diseases."
The next step for the team is to test the effects of inflammation on other areas of brain function such as memory.
Leonie JT. Balter, Jos A. Bosch, Sarah Aldred, Mark T. Drayson, Jet JCS. Veldhuijzen van Zanten, Suzanne Higgs, Jane E. Raymond, Ali Mazaheri. Selective effects of acute low-grade inflammation on human visual attention. NeuroImage, 2019; 202: 116098 DOI: 10.1016/j.neuroimage.2019.116098