Even mild or asymptomatic cases of COVID-19 may still have lasting effects on people’s ability to remember specific long-term events or personal experiences, according to a new study published today from researchers at Oxford University.
Medical experts have known about long COVID—when patients report lasting symptoms for much longer than one might expect after infection—for quite some time. While long Covid cases have differed from person to person, common symptoms include chronic fatigue, labored breathing, and the loss of smell or taste. These symptoms can persist for months.
Most cases of long COVID have been connected to patients who contracted severe illness. But this new study, which looked at 136 participants, found that brain fog symptoms could appear and persist for up to nine months in people who contracted even light cases of COVID. Those symptoms include forgetfulness, low motivation, difficulty concentrating, and general moodiness.
The study included 53 participants who had contracted relatively mild cases of COVID in the past, and a control group of 83 people who had never had COVID. The participants were asked to complete a number of tests to assess their memory, with a focus on tasks that required cognitive abilities important to daily life, like sustaining attention, memory, and reasoning skills.
Recovered COVID patients displayed significantly worse episodic memory—the ability to remember specific events or personal experiences in the past—and had much shorter attention spans than people who had never contracted COVID.
“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,” Dr Sijia Zhao of Oxford’s Department of Experimental Psychology, University of Oxford, said in a statement.
The study found that shorter attention spans and dampened episodic memory observed in people who had recovered from mild COVID tended to last up to nine months after infection.
But even though some of the brain fog symptoms associated with long COVID tended to persist far longer than normal, over time each participant in the study was able to recover.
The study’s authors are unsure as to exactly why mild COVID infections could cause these lasting cognitive symptoms, but were heartened that all study participants eventually showed signs of recovery.
“We still do not understand the mechanisms that cause these cognitive deficits,” said Dr. Masud Husein, professor of cognitive neurology at Oxford. “[B]ut it is very encouraging to see that attention and memory return largely to normal in most people we tested by 6-9 months after infection.”
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