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Cutting through the fog: understanding the causes of mental fatigue

Written by Caitlin Killen

New study provides an explanation for the brain fog often experienced by those with chronic medical conditions.

Individuals with chronic medical conditions often experience severe mental fatigue or ‘brain fog’. This fatigue can affect mental processes such as memory, the ability to process information and problem-solving skills. Increased mental strain can be frustrating and exacerbate existing symptoms of chronic illness.

Now, a collaborative study between scientists at the University of Birmingham (UK) and the University of Amsterdam (The Netherlands) has provided a possible explanation for this symptom.

Inflammation is the body’s response to infection; it is also found in autoimmune diseases. The team demonstrated a link between inflammation and a decline in the brain’s cognitive responses.

“Scientists have long suspected a link between inflammation and cognition, but it is very difficult to be clear about the cause and effect,” explained senior author Ali Mazaheri (University of Birmingham).

The study enrolled 20 healthy male volunteers. Each participant received a salmonella typhoid vaccine – selected to induce temporary inflammation with minimal side effects – on one day, and a saline injection which served as a placebo-control on another.

A few hours after receiving each injection, the volunteer’s cognitive responses were tested. Electroencephalography was utilized to image brain activity in response to different stimuli. Three separate attention processes were examined in order to understand the processes happening in distinct regions of the brain.



The processes examined were: “alerting” to assess vigilance in preparation for potential stimuli, “orienting” which is the ability to identify and prioritize sensory information and “executive control” which identifies the ability to process conflicting information.

The volunteers’ inflammatory levels were assessed by testing levels of interleukin-6 in the blood on each day of the study. It was demonstrated that inflammation impeded alertness, while the performance of the other attention processes was unaffected.

“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,” commented Leonie Balter (University of Amsterdam), first author of the paper.

These findings demonstrate that inflammation results in individuals exerting a greater cognitive effort when carrying out day to day tasks. The team now aims to assess the effects of inflammation on memory and other areas of brain function.