A novel study led by researchers from the University of Oxford has investigated the lingering cognitive effects of mild COVID-19 in the months following infection. The research revealed minor deficits in attention and memory can be seen for up to six months following a mild infection.
It is becoming increasingly clear that a severe case of COVID-19 can result in lasting impacts to the brain. Alongside these acute impacts on the brain, there are persistent cognitive deficits being reported by long COVID patients that last months past an initial infection.
This new study, published in the journal Brain Communications, set out to investigate the other end of the disease spectrum. Here, the focus was on cognitive impacts in asymptomatic to moderate COVID-19 patients who do not report symptoms of long COVID.
More than 150 subjects were recruited for the study, with around 60 reporting a PCR-confirmed case of mild COVID-19 up to nine months prior. The cohort completed 12 different online tests designed to measure a range of cognitive functions, from sustained attention and semantic reasoning to mental rotation and spatial–visual attention.
“Reassuringly, COVID-19 survivors performed well in most abilities tested, including working memory, executive function, planning and mental rotation,” the authors write in the new study. “However, they displayed significantly worse episodic memory (up to six months post-infection) and greater decline in vigilance with time on task (for up to nine months).”
The vigilance task is used to evaluate how quickly a person is fatigued during a cognitive exercise demanding consistent attention. Compared to a control group the COVID patients displayed rapid declines in accuracy on the task after about four minutes of concentration.
Sijia Zhao, an author on the new study from the University of Oxford, said it was surprising to see these minor cognitive deficits in the recovered COVID-19 subjects because none of the cohort were subjectively reporting any neurological problem.
“What is surprising is that although our COVID-19 survivors did not feel any more symptomatic at the time of testing, they showed degraded attention and memory,” said Zhao. “Our findings reveal that people can experience some chronic cognitive consequences for months.”
It is unclear exactly what could be causing these specific impairments so many months after an initial infection. The researchers hypothesize the virus may be causing a variety of immunological and microvascular changes in the brain. But the good news is, as study co-author Masud Husain explained, these potential cognitive impairments seem to disappear between six and nine months after initial infection.
“We still do not understand the mechanisms that cause these cognitive deficits, but it is very encouraging to see that these attention and memory return largely to normal in most people we tested by six to nine months after infection, who demonstrated good recovery over time,” Husain said.
Stephen Burgess, a researcher from the University of Cambridge who did not work on this project, pointed out a number of limitations in the small study. He said the lack of randomization and blinding means the differences detected between COVID and non-COVID groups should be interpreted cautiously. But he does indicate the findings are certainly striking, and worthy of further investigation.
“… differences between the COVID and non-COVID groups in terms of several specific measures of cognitive ability looked at in this study were striking, particularly in terms of delayed memory tasks and ability to perform tasks accurately when fatigued,” said Burgess. “Despite the limitations of non-randomized research, it seems unlikely that these results can be explained by systematic differences between the groups unrelated to COVID infection.”
The new study does conclude by noting it is plausible to assume transient minor cognitive deficits would be apparent following mild COVID-19 cases. Considering prior studies have indicated symptom severity at the time of infection is linked to severity of persistent neurological problems it is unsurprising mild COVID-19 cases can display minor signs of the same problems detected after severe cases.
“Just as the acute illness of COVID-19 demonstrates a wide severity spectrum from asymptomatic to fatal forms, our findings show that post-COVID cognitive deficits too can also manifest a wide severity spectrum,” the authors concluded in the study. “They highlight a pressing need to measure cognitive performance objectively in order to better understand how the brain is affected by COVID-19.”
The new study was published in the journal Brain Communications.
Source: University of Oxford
