Daily brain tests could reveal how prepared your immune system is to tackle a future viral infection.

A study led by researchers at the University of Michigan (U-M) has shown that poor immune performance tends to go hand-in-hand with periods of fluctuating cognitive performance.

For the first few days of the eight-day study, 18 participants tested their attention, reaction time, and ability to switch between numbers and symbols three times a day. On the fourth day of the study, the group was purposefully exposed to the human rhinovirus (HRV), typically responsible for the common cold.

Over the remaining days, a nose wash was self-administered by participants to measure the presence and volume of shedding viral cells.

Volunteers were also asked to rate their experience of eight symptoms, including chills, cough, headache, nasal obstruction, runny nose, sneezing, sore throat, and tiredness.

Ultimately, those who shed the most virus and had the worst symptoms tended to show inconsistent cognitive scores in the days leading up to their sickness.

"In the beginning, we didn't find that cognitive function had a significant association with susceptibility to illness because we used the raw scores," says bioinformatics researcher Yaya Zhai at U-M.

"But later, when we looked at change over time, we found that variation in cognitive function is closely related to immunity and susceptibility."

In other words, a single, one-off test probably isn't enough to determine the state of a person's immune system. A trend of cognitive performance as measured over days, however, could be the ticket.

The authors of the study acknowledge that most people are unlikely to take a cognitive test three times a day for the rest of their lives. But their results still showed strength even when only five tests were accounted for so long as they began three days before infection and at least one test was taken a day.

In the real world, a person doesn't know when they will next be exposed to a virus. That means for brain tests to predict future immune responses, they probably need to be taken semi-regularly. How regular remains to be determined.

The current study is small and only hints at a possible connection between cognitive function and a healthy immune system. Further research among larger cohorts is needed to verify the results.

In the past, scientists investigating brain function and health have relied on raw cognitive scores. But emerging research suggests the ups and downs of brain tests hold more information than any one test on its own.

An impressive 19-year-long study, for instance, found that when a person's reaction times show higher variability on tests, that person is at a greater risk of falls, neurodegenerative disorders, and death.

The authors of the current study hope that one day, brain tests can be easily accessed and tracked by the public using their very own smartphones.

Information on an individual's typing speed, typing accuracy, and sleep time, for instance, could be combined with tests on attention and memory to better predict when they are at a heightened risk of severe illness.

Precautionary measures could then be taken to reduce their exposure, or sure up their body's defenses.

"Traditional clinical cognitive assessments that look at raw scores in a single time point often do not provide a true picture of brain health," explains neuroscientist P. Murali Doraiswamy from Duke University.

"At home, periodic cognitive monitoring, through self-test digital platforms, is the future of brain health assessment."

The study was published in Scientific Reports.