The Relationship Between COVID and Cognitive Function
Post by Anastasia Sares
The takeaway
A new meta-analysis showed that having COVID-19 (even a mild to moderate case) was linked to lower performance on cognitive tests after a person was no longer infected. Severe cases were linked to worse performance than mild or moderate cases. This is part of a larger pattern for viral diseases in general.
What’s the science?
Getting infected with SARS-CoV-2—the virus that causes COVID-19—can lead to symptoms like fatigue and brain fog, which sometimes last long after a person has recovered from the virus itself. In light of these symptoms, it is important to understand what effect COVID-19 may have on the public's long-term cognitive health. We need to know whether people’s self-reported cognitive issues correspond to actual performance on cognitive tests—in other words, an objective cognitive impact. Many studies were published on this topic during the years of the pandemic, but to better understand the trends, we need more than a lot of individual studies. Each study has slightly different methods and is conducted on a different group of people. Meta-analysis is a technique that takes the results from many different studies and aggregates them to help us come to an overall conclusion.
Recently in Neuropsychology Review, Austin and colleagues conducted a meta-analysis to understand the objective cognitive effects of COVID-19 infection.
How did they do it?
The authors sifted through multiple databases of scientific literature using keywords related to Sars-Cov-2/COVID and cognitive functioning, searching specifically for studies that evaluated cognition after the initial acute phase of the disease. They eliminated studies that were duplicates, did not address their main questions, did not involve mild to moderate COVID cases, or did not include objective measures of cognitive functioning (among other criteria). Then, they divided the studies into three categories: first, those that compared cognitive performance between a non-COVID control group and a mild-COVID group, second, those that compared the performance of a mild COVID group to an established testing norm, and third, a group mild or moderate COVID versus a group with severe COVID symptoms. The prediction was that the COVID groups would perform worse overall than the standardized norms as well as the control groups and that severe COVID would lead to worse performance than mild or moderate COVID.
What did they find?
In all three groups, scores across the cognitive testing spectrum were lower for the COVID groups. Memory, language, and combined measures were significantly affected. In addition, the groups with severe COVID performed worse than those with mild or moderate COVID in attention, memory, and executive function. However, visuospatial functioning was not affected. It is important to mention that the size of these effects was not large and differed quite a bit across studies; they were most pronounced in those with long-lasting symptoms after their illness. The authors gave some possible explanations for why COVID might lead to cognitive symptoms. The virus could have direct effects on brain tissue, or it may contribute indirectly via neural inflammation and other stress-induced processes. People may also experience distraction due to ongoing physical pain or depressive symptoms. These ideas are based on what we know about similar dynamics in other viral diseases such as influenza, herpes, and hepatitis. Ultimately, there are many questions left to be answered, especially as this virus evolves and changes over time.
What’s the bottom line?
As COVID-19 transitions from being pandemic (new and spreading out of control) to endemic (constantly present in the population but more predictable), it is important to understand how it affects cognitive health, especially since the population is also aging in many countries. Given this new risk to cognitive health, it is more important than ever to focus on finding therapies that can prevent or slow cognitive decline.