In late 2019, the BBC2 Horizon television network in England launched a national campaign it called The Great British Intelligence Test,
A collaborative citizen science project conducted by a team of brain researchers from the United Kingdom and the U.S., their goal was to enable viewers to assess their cognitive strengths.
Not an IQ test per se, participants took nine tests evaluating planning and reasoning skills, working memory, attention and emotion processing abilities, then filled out a questionnaire about their personal background.
People were drawn in by the ability to compare their score to those of others, and the turnout was huge. At one point, more than 36,000 viewers crashed the webpage for sign-ups, and by last fall, the participant count had surpassed 84,000 adults.
Because it had been launched before COVID-19, moreover, none of the promotional materials mentioned the illness at all.
But once the illness set in, the organizers saw an opportunity to learn more about the mystery illness, and reworded their discharge questionnaire to probe each participant’s patient status in connection to the illness –including whether they were hospitalized and put on a ventilator in the ICU.
Because the participants did not know the test would ask them about their COVID-19 history (or lack thereof), it offered the rare example of a cross sectional survey — a method that cannot prove causality, but can capture a broad range of information during a short window of time — which did not load the deck with people hoping to study the effects of their illness.
If anything, it was biased towards the broad swath of the population that wants to know more about how smart they are.
Once all the data had been collected, the authors checked if global cognitive scores varied according to COVID-19 respiratory symptom severity, and did so after controlling for the effect on cognitive skill of age, education level, earnings, occupational status and other variables.
Out of 84,285 participants, more than 9,200 had said they contracted the illness, with more than 3,400 having suffered breathing problems at home, 176 seen by a doctor, 147 hospitalized without a ventilator, and 60 hospitalized on a ventilator.
So, what did they find out?
Generally, that you don’t want to get COVID-19 if you can avoid it.
Even if you think it won’t kill you.
Specifically, the study found those who were sick with COVID-19 at home had small but significant global performance deficits in their cognitive abilities, while people who were hospitalized with the illness had medium and large deficits, depending upon the severity of their course of illness.
A cautionary note, the study was published on the preprint server medRxiv and as such is not yet peer-reviewed, meaning it should not be used to guide treatment decisions.
At its worst, the deficit in those who were put on a ventilator with the illness was larger than that experienced by those who had suffered a stroke.
This effect equalled the ordinary cognitive drop-off in adults over a 10-year period, or an 8.5-point drop in IQ on average. What does that look like? You might search a little longer to find the word you were looking for, or your executive functioning could slow down.
It could take you longer to decide how to plan a trip with multiple flights.
According to the authors, if only those who had been placed on a ventilator saw their executive functioning drop, it might not have been surprising, as the experience is known to create certain deficits.
But they found COVID-19 negatively affected the cognitive scores of people who were treated at home, and the authors wondered if this indicated “less severe hypoxia.”
Hypoxia, or the depletion of oxygen to the brain, is known to make high-altitude climbers lose their cognitive functioning in the short term.
The authors addressed the other nagging skeptical question: if the study reflected the possibility that “people with lower cognitive ability have higher risk of catching the virus.”
We know, everyone reading that sentence who has already caught COVID-19 is now feeling judged. You can relax. A simple, COVID-19/dull-witted correlation would not explain, the authors said, why study participants with worse illness had worse deficits.
The authors called for longitudinal research and follow-up with the same subjects to determine if the results are lasting and unique to COVID-19, or affect other respiratory diseases.