When someone's knee becomes inflamed, he or she might experience reduced range of motion, which can disrupt his or her ability to walk normally. When someone suffers from inflammation in the brain, similarly, cognitive function becomes crippled.

Neuroinflammation is a well-known characteristic of neurodegenerative diseases like Alzheimer's, Parkinson's and forms of dementia. This swelling contributes to the rate of progression for these diseases.  

According to new research, increased inflammation following an infection hinders the brain's ability to create spatial memories. The findings, published in the journal Biological Psychiatry, are the first of this kind to image the effects of inflammation on the brain.

In the initial trial to understand how inflammation inhibits memory, a team of researchers at Brighton and Sussex Medical School scanned 20 participants before and after either a typhoid vaccination or benign salty water injection, which was used to trigger inflammation. Positron emission tomography was used to gauge the impact of inflammation on the consumption of glucose in the brain. After each scan, the subjects put their spatial memory to the test by performing a number of tasks in a virtual reality program.

"We have known for some time that severe infections can lead to long-term cognitive impairment in the elderly. Infections are also a common trigger for acute decline in function in patients with dementia and Alzheimer's disease," Dr. Neil Harrison, a Wellcome Trust intermediate clinical fellow at BSMS who led the study, told Eureka Alert in a statement. "This study suggests that catching a cold or the flu, which leads to inflammation in the brain, could impair our memory."

Following the inflammation, the scientists noticed a reduction in glucose metabolism within the brain's memory system, called the medial temporal Lobe (MTL). The MTL is responsible for storing long-term memories for facts and events, especially for visual recollections, comprehending language and deriving meaning from things like pictures. In patients who have sustained damage to their MTL, amnesia is profoundly common.

Participants performed less well in spatial memory tasks, a result that appeared to have a direct link in the change in MTL metabolism. In short, the cognitive impairment was induced by a decrease in glucose metabolism in the brain's memory center, interfering with the neural circuits which play a crucial role in learning and memory.

Stakes for seniors
While infections are not likely to have a long-term detrimental impact in the young and healthy, the findings hold major implications for older Americans' standards of senior wellness – in particular those suffering from dementia.

"Our findings suggest that the brain's memory circuits are particularly sensitive to inflammation and help clarify the association between inflammation and decline in dementia," Harrison remarked to the source. "If we can control levels of inflammation, we may be able to reduce the rate of decline in patients' cognition."

Dementia currently affects 35.6 million people worldwide, according to the World Health Organization. This number is expected to double by 2030 and more than triple by 2050. In the U.S. alone, as many as 6.8 million people have dementia, based on numbers from the National Institute of Neurological Disorders and Stroke. Alzheimer's disease is the most common form of dementia.

The findings from Brighton and Sussex could help encourage the development of new drugs focusing on the immune system as a method to treat dementia. The easy accessibility of blood immune cells and markers makes them prime candidates for use as potential biomarkers.

Harrison and colleagues plan to further pursue the role of inflammation in dementia, including how acute infections such as influenza affect the rate at which neurodegenerative diseases progresses.