Viruses Affect Memory

Recent research looks at how viral infections can involve the brain, affecting how the memory works. In fact, some of the incidental memory degeneration associated with ageing may be due to past viral infections. Aetiology Blog looks at this issue.

A recent article highlights one area of investigation: how viral infections can influence memory problems......

A family of viruses that cause a range of ills from the common cold to polio may be able to infect the brain and cause steady damage, a team at the Mayo Clinic in Minnesota reported on Monday.

"Our study suggests that virus-induced memory loss could accumulate over the lifetime of an individual and eventually lead to clinical cognitive memory deficits," said Charles Howe, who reported the findings in the journal Neurobiology of Disease. [Article can be found here; --TS]

This may seem somewhat far-fetched at first, but we know that viruses certainly can cause severe damage to the brain and nervous system. Therefore, this lends plausibility to the idea that they can cause more minor damage as well. As they note, polio (a picornavirus) is a prime example of this, with the potential to affect the brain and the spinal cord and result in paralysis. A related virus in mice, called Theiler's murine encephalomyelitis virus, has also been used to induce damage to the nervous system (for example, it's used as a mouse model for multiple sclerosis), and researchers infected mice with this and then performed cognitive tests to see if it had more subtle effects as well:

Infected mice later had difficulty learning to navigate a maze. Some were barely affected, while others were completely unable to manage, and when the mice were killed and their brains examined, a correlating amount of damage was seen in the hippocampus region, related to learning and memory.

Now, it's always a bit difficult to extrapolate directly from an animal model to humans, but the study is certainly intriguing and can open doors for epidemiological studies of viruses and cognition in humans.

One virus particularly likely to cause brain damage is enterovirus 71, which is common in Asia, the researchers said. It can cross over into the brain and cause encephalitis, a brain inflammation that can lead to coma and death.

"Our findings suggest that picornavirus infections throughout the lifetime of an individual may chip away at the cognitive reserve, increasing the likelihood of detectable cognitive impairment as the individual ages," the researchers wrote in their report.

"We hypothesize that mild memory and cognitive impairments of unknown etiology may, in fact, be due to accumulative loss of hippocampus function caused by repeated infection with common and widespread neurovirulent picornaviruses."

Source.

The link to this story came from Tangled Bank #65. There are many more good stories to be found from this edition, so check them out.

This is a particularly disturbing concept--one that has probably spawned a large number of zombie stories and other tales of malignant mass mental transformations. Vaccines have minimised incidence of bacterial meningitis, which previously destroyed the minds of many thousands of people every year--at least in the western world. Neurovirulent viruses can be more difficult to control.