Scientists at the University of Birmingham in collaboration with the University of Amsterdam have uncovered a possible explanation for the mental sluggishness that often accompanies illness.
An estimated 12M UK citizens have a chronic medical condition, and many of them report severe mental fatigue that they characterize as 'sluggishness' or 'brain fog.' This condition is often as debilitating as the disease itself.
A team in the University's Centre for Human Brain Health investigated the link between this mental fog and inflammation - the body's response to illness. In a study published in Neuroimage, they show that inflammation appears to have a particularly negative impact on the brain's readiness to reach and maintain an alert state.
The study focused specifically on an area of the brain which is responsible for visual attention. A group of 20 young male volunteers took part and received a salmonella typhoid vaccine that causes temporary inflammation but has few other side effects. They were tested for cognitive responses to simple images on a computer screen a few hours after the injection so that their ability to control attention could be measured. Brain activity was measured while they performed the attention tests.
On a different day, either before or after, they received an injection with water (a placebo) and did the same attention tests. On each test day they were unaware of which injection they had received. Their inflammation state was measured by analyzing blood taken on each day.
The tests used in the study assessed three separate attention processes, each involving distinct parts of the brain. These processes are: "alerting" which involves reaching and maintaining an alert state; "orienting" which involves selecting and prioritizing useful sensory information; and "executive control" used to resolving what to pay attention to when available information is conflicting.
The results showed that inflammation specifically affected brain activity related to staying alert, while the other attention processes appeared unaffected by inflammation.
The next step for the team will be to test the effects of inflammation on other areas of brain function such as memory.