Does the Flu Affect Your Mind? Bad Memory and Brain Changes Could Result After the Viral Infection

Did you get the flu this year? There’s a chance it may have a long-lasting effect on your brain. Research published Monday in the Journal of Neuroscience found that for months after mice got the flu, their memory was impaired.

For this study, mice were infected with a strain of the flu and put in something called a Morris water maze—basically a pool of water with a submerged platform that the mice can’t see. Each time the mice go into the maze, they swim around until they touch the platform. (Treading water gets pretty tiring, after all.)

There are cues, like letters or colored bits, spread around the pool. After a few times out, mice should learn where the platform is based on these cues—unless they have memory problems.

Mice infected with the flu went through this test four times over six months—and for at least two months, they took far longer than expected to find the platform. The test was done at 30, 60, 90 and 120 days after infection. “One hundred and twenty days after the infection, they’ve fully recovered,” Martin Korte, a biologist at Technische Universität Braunschweig in Germany, told Newsweek. “They get back their full cognitive abilities—but one has to keep in mind that 120 days for the lifespan of a mouse would be equivalent to many years in humans.”

This change may be happening because the brain’s version of an immune system continues to be triggered long after the sniffles subside. “The inflammatory response in the brain holds on much longer than the actual virus is around,” he said. Two kinds of cells in the brain are responsible for this inflammatory response: astrocytes and microglia. (Activation of microglia is also thought to be involved in Alzheimer’s as well as other conditions.)

Exactly how the virus might be having this effect isn’t clear. But this isn’t the first time that scientists have found evidence of an infection causing brain inflammation. Richard Smeyne, a neuroscientist at Thomas Jefferson University who was not involved in this paper, has been studying a potential link between viruses and Parkinson’s disease for years. “Our findings actually support the findings of this paper,” he said. “Any virus that gets into the brain becomes much more worrisome in terms of later effects.”

Smeyne said he was particularly concerned by the effects of the H3N2 virus, given that it is a virus strain we see often in humans. This is the strain that has been responsible for much of the devastating flu season in the United States this winter.

Results of a similar study done in humans really ought to have the same results, but it would be impossible to know without more studies. That's always true, but especially for this study, Smeyne noted, because Korte and his colleagues used strains of the flu that had been adapted to infect and spread among mice, not the actual strains of flu humans encounter. There are good reasons to use those mouse-adapted strains—the safety of the researchers, for example—but that adaptation necessarily means that the flu is just a little bit different.

If these findings turn up again in human studies, it would be nice to do something about it. Korte is on it. “We would like to know if we protect the mice with the same antidotes we are using [like Tamiflu] if they are also protected from the neurological effects,” he said.

Those studies are already ongoing, and Smeyne thinks that intervention might actually work. In animal studies, he said, mice that were vaccinated against the flu didn’t have this kind of immune response in their brains if they did get the virus. That might mean that getting a flu shot might be even more important than we realize.

“You may still get the flu, but it might protect you against this kind of longer-term inflammation,” Smeyne said. “I hate to be the scary guy, but I think these are concerns that we have to have.”