A new study led by Western University neuroscientists is shedding more light on COVID-19’s impacts on post-infection cognitive function.
The study, published Tuesday in the journal Cell Reports Medicine, found short and possibly long-term cognitive impacts in processing speed, reasoning, verbal, and overall cognitive performance among the nearly 500 participants who took part. The study ran online from June 2020 to February 2021.
“Not all cognitive abilities were affected equally,” said Adrian Owen, a professor of cognitive neuroscience and imaging at Western’s Brain and Mind Institute, and one of the study’s lead authors.
“Memory, for example, was completely unaffected. We didn’t find any memory impairment. People may think they have a memory problem, but actually when it was tested in a lab situation, they don’t.
“The real problems were with slow thinking. People were very slow to solve the problems we gave them and to make decisions.”
Owen and the other researchers, including Western’s Conor Wild and others from UBC, Cambridge University, and Sunnybrook Health Sciences Centre, focused on 478 adult volunteers from Canada, Germany, Spain, the U.S. and the U.K. who had self-reported a positive test for COVID-19.
Those taking part in the online study varied in age, averaging around 43-years-old, and included 412 people who had not been hospitalized for COVID-19, and 66 who had been, including 34 who required supplemental oxygen, 17 who were in intensive care, and 11 who had been on a ventilator.
More than 3,200 people originally registered to take part in the study, and just over 1,400 completed the cognitive tests, however that number was whittled down after researchers removed outliers and datasets containing incomplete questionnaires, ineligible age entries, and other issues.
The study, conducted online, tested the participants three months after a confirmed diagnosis of COVID-19 using an online cognitive tool from Cambridge Brain Sciences, which Owen co-founded. Owen and Wild had previously utilized the tool in 2017 as part of a sleep study involving more than 40,000 people.
Participants were asked about their COVID-19 history, and were given 12 tests using the tool, including tests focused on short-term memory, episodic memory, verbal working memory, deductive reasoning, planning and executive functioning, and verbal reasoning.
Researchers found that those in the COVID-19 study performed significantly worse compared to those in the 2017 study in processing speed, reasoning, verbal, and overall performance — resembling the results of those from the sleep study who were sleep-deprived, Owen says.
“At three months, these things had neither got better or worse. That could be both good or bad news. I mean, I guess on the good side, it means that this doesn’t look like it’s something that will deteriorate over time. On the other hand, it doesn’t look like it’s getting any better either,” Owen said.
In addition, those who had suffered more severe COVID-19 infections, such as those who had been hospitalized, appeared to experience more severe cognitive impairments, particularly in reasoning and processing speed. The study also notes that participants who had better than average physical health performed similar to those in the normative data from 2017 in all cognitive domains.
“There was an interesting dissociation between that and the effects on mental health. About 30 per cent of our sample actually scored within a clinical range for things like depression and anxiety,” Owen said.
“So as well as the effects on cognition, there were effects on mental health, but importantly the mental health effects were not related to the severity of the disease.”
He noted, however, that the direct and indirect effects of living through the COVID-19 pandemic itself may explain why mental health effects were not tied to COVID-19 severity.
“One of our interesting findings was the relationship between older people and younger people. The older you are, the more likely you are to have more severe cognitive impairments following a COVID-19 infection. But it’s the opposite for mental health impairments. The younger you are, the more likely you were to have problems with anxiety and depression,” he said.
Owen says he found the relationship between mental health outcomes and cognitive outcomes to be surprising, noting that oftentimes issues related to mental health, such as severe depression, can also result in cognitive impairments.
“The fact that these two things were completely decoupled, in a sense there might be two quite separate aspects of COVID-19 infection, one affecting cognition, one affecting mental health, was surprising to me,” he said.
“It’s also very informative because it suggests, quite possibly, that the underlying brain mechanisms are different … that the way COVID-19 is affecting the brain varies amongst different people, and it might be affecting different brain systems in different ways.”
The study’s findings come a day after Statistics Canada released new data showing that around 1.4 million Canadian adults who know or suspect they’ve had COVID-19 reported experiencing symptoms. The data was released in partnership with the Public Health Agency of Canada.
Fatigue was the most common symptom, experienced by almost three-quarters of those with long-term symptoms, followed by cough and shortness of breath at 39 per cent and brain fog at 33 per cent, according to the Stats Can figures.
Similarly to the Western study, the Statistics Canada data also shows people who experienced more severe symptoms from their initial COVID-19 illness were more likely to experience longer-term symptoms.
Nearly one in three Canadians who experienced symptoms for at least three months after getting COVID-19 say they had recovered from their initial illness before symptoms returned.
During the time data was collected for the Western study, from June 23, 2022 until Feb. 2, 2021, the original SARS-CoV-2 virus was the only, or dominant, strain circulating.
Asked if researchers would conduct a follow-up study to examine whether subsequent COVID-19 variants may result in different cognitive outcomes, Owen noted the challenges in obtaining such data.
“As in all sort of scientific studies of this type, the more variables you throw into the equation, the more complex everything gets. And once we started to have multiple variants and multiple types of infection, it started to become very difficult to track the data,” he said.
“Most people don’t know what variant they have. They can hazard a guess based on when it occurred, but that’s not information that people typically have fed back to them, so for us to get hold of that information would actually be rather difficult.”
Those looking to take the same assessment used by the study’s participants can do so through the website of Cambridge Brain Sciences.
The full study can be found on the website of Cell Reports Medicine.
— with files from Teresa Wright
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