It is becoming increasingly clear that a severe case of COVID-19 can have long-lasting effects on the brain, and along with these are persistent cognitive deficits reported by long-term COVID patients, lasting for months after an initial infection.
Under that context, a group of researchers from the University of Oxford set out to study the cognitive impacts in asymptomatic and moderate COVID-19 patients who did not report symptoms of prolonged COVID.
The results of the study, which was published in the journal Brain Communicationsrevealed that minor deficits in attention and memory can be seen up to six months after a mild COVID infection.
More than 150 people were recruited for the study, of whom 60 reported a mild case of COVID-19 confirmed by PCR up to nine months earlier. The group completed 12 online tests designed to measure a variety of cognitive functions, from sustained attention and semantic reasoning to mental rotation and visuospatial attention.
“Encouragingly, the COVID-19 survivors performed well on most skills tested, including working memory, executive function, planning, and mental rotation. However, they showed significantly worse episodic memory (up to six months post-infection) and a greater decline in vigilance with time spent on task (up to nine months).”
The vigilance task is used to assess how quickly a person becomes fatigued during a cognitive exercise that requires constant attention. Compared to a control group, the COVID patients showed a rapid decline in task accuracy after about four minutes of concentration.
Sijia Zhao, an author of the new study, said it was surprising to see these minor cognitive deficits in recovered COVID-19 subjects, because none of the group subjectively reported any neurological problems.
“What is surprising is that although our COVID-19 survivors felt no further symptoms at the time of testing, they did show degraded attention and memory. Our findings reveal that people can experience some chronic cognitive consequences for months,” Zhao said.
Exactly what might be causing these specific deficiencies so many months after an initial infection is not known, but the researchers hypothesize that the virus may be causing a variety of immunological and microvascular changes in the brain.
The good news is that, as study co-author Masud Husain explained, these potential cognitive problems appear to go away six to nine months after the initial infection.
“We don’t yet understand the mechanisms that cause these cognitive deficits, but it’s very encouraging to see attention and memory return largely to normal in the majority of people we evaluated six to nine months after infection, who showed good recovery over time,” Husain said.
On the other hand, Stephen Burgess, a researcher at the University of Cambridge who was not involved in the new study, pointed out a number of limitations to the research. He mentioned that the lack of randomization and blinding means that the differences detected between groups with and without COVID should be interpreted with caution. But he does indicate that the findings are certainly impressive and worthy of further investigation.
“The differences between the COVID and non-COVID groups, in terms of several specific measures of cognitive ability observed in this study, were impressive, particularly in terms of delayed memory tasks and the ability to perform tasks accurately when fatigued.” Burgess said.
“Despite the limitations of nonrandomized research, it seems unlikely that these results can be explained by systematic differences between groups unrelated to COVID infection,” added the outside researcher.
The new study concludes by stating that it is plausible to assume that transient minor cognitive deficits would be evident after mild cases of COVID-19. Considering that previous studies have indicated that the severity of symptoms at the time of infection is related to the severity of persistent neurological problems, it is not surprising that mild cases of COVID-19 may show lesser signs of the same problems seen in serious cases.
“Just as acute COVID-19 disease demonstrates a wide spectrum of severity, from asymptomatic to fatal forms, our findings show that post-COVID-19 cognitive deficits can also manifest a wide spectrum of severity. They highlight a pressing need to measure cognitive performance objectively to better understand how COVID-19 affects the brain.”
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