People who have had covid-19 may have long-term cognitive impairments, but memory appears to be less affected.
|Covid-19 can impair cognition. Dragana Gordic/Shutterstock
People who have had covid-19 can have long-term cognitive impairments, but memory appears to be less affected.
While it is now widely accepted that covid-19 can cause long-term declines in cognition, among other symptoms, most previous studies evaluating this used dementia-related tests. "These tests don't provide very subtle measures, and they don't really measure a variety of brain functions," says Conor Wild, a psychology professor at Western University in Ontario, Canada.
Wild and his colleagues used the Cambridge Brain Sciences online cognitive assessment tool to provide a more sensitive analysis, which measures cognition using 12 tasks across five domains: reasoning, verbal processing, memory, processing speed, and overall cognition.
The researchers asked 478 adults who had previously been infected with covid-19 to take the test. Participants tested positive between one week and nine months before the study, and it is unknown if any had previously contracted the virus. Approximately 14% reported being hospitalized as a result of their illness.
The researchers then compared the scores of the participants to those of 7832 people who completed the assessment prior to the pandemic. They discovered that people who had previously reported a covid-19 infection had significantly lower overall cognitive scores - the equivalent of aging by 4.5 years, according to Wild. Those with more severe infections fared the worst, but even those with minor illnesses suffered impairments.
Covid-19 appeared to have a greater impact on certain brain functions than others. According to Wild, processing speed was the most impaired, with average scores lower than the control group by the equivalent of 8.5 years. On average, those who reported contracting covid-19 had significantly lower verbal processing and reasoning scores.
Notably, the researchers found no significant differences in memory, despite previous research findings. "Memory is sort of an umbrella term that encompasses a few different types of memory," Wild explains. He claims that the assessment tool used in this study is biased toward short-term memory, which could explain the discrepancies.
We can not only better understand long covid by pinpointing which areas of cognition covid-19 affects, but also potentially develop more precise treatments for the condition, says Frederic Meunier of The University of Queensland in Australia.
Previous research, for example, has shown a similar pattern of impairment in people who don't get enough sleep, with reductions in processing and overall cognition but not memory, suggesting that the effects of covid-19 may be related to sleep disturbances.
However, because the researchers compared the scores of people with a history of covid-19 to those of people studied before the pandemic, they can't say for certain that the observed differences were caused by illness. According to Wild, the stress of living through a pandemic could have also played a role.
"What we're looking at next is how people compare to their pre-pandemic selves in terms of cognition," he says.
Cell reports Medicine, DOI: 10.1016/j.xcrm.2022.100750