Why Inflammation Impairs Memory as We Age

Inflammation has long been linked to disorders of memory such as Alzheimer's disease. Severe infections can also impair cognitive function in healthy elderly individuals. Now new research done at Brighton and Sussex Medical School in the UK and published in the journal Biological Psychiatry not only helps explain why inflammation impairs memory but could spur the development of new drugs targeting the immune system to treat dementia.

A release from Wellcome Trust, a global charitable foundation dedicated to achieving improvements in human and animal health,reports the team scanned 20 participants before and after either a benign salty water injection or typhoid vaccination used to induce inflammation. Positron emission tomography (PET) measured the effects of inflammation on the consumption of glucose in the brain and after each scan participants tested their spatial memory by performing a series of tasks in a virtual reality.

A reduction in glucose metabolism within the brain's memory center, known as the Medial Temporal Lobe (MTL), showed up following inflammation. Participants also performed less well in spatial memory tasks, an effect that appeared to be directly mediated by the change in MTL metabolism.

The release quotes lead researcher Dr Neil Harrison, a Wellcome Trust Intermediate Clinical Fellow at BSMS, as saying, "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. This study suggests that catching a cold or the flu, which leads to inflammation in the brain, could impair our memory."

Infections are unlikely to cause long-term detrimental impact in the young and healthy but the findings are of great significance in the elderly. The team now plans to investigate the role of inflammation in dementia, including insight into how acute infections such as influenza influence the rate of progression and decline.

"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," says Dr Harrison. "If we can control levels of inflammation, we may be able to reduce the rate of decline in patients' cognition."