Individuals who recovered from COVID-19, including those who no longer had symptoms, exhibited significant “cognitive deficits,” according to a large study out of the U.K.
The research, conducted by academics from Imperial College London, Kings College and the Universities of Cambridge, Southampton and Chicago, aimed to find out how COVID-19 affected mental health and cognition.
For the study, researchers analyzed data from 81,337 participants of the Great British Intelligence Test from January to December 2020. Of those participants, nearly 13,000 reported they had contracted the novel coronavirus.
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Importantly, the study said that only 275 participants had completed the intelligence test both before and after contracting COVID-19.
For the rest of the participants, the researchers said they employed a linear model to predict general cognitive performance, or premorbid intelligence, based on age (to the third order), sex, handedness, ethnicity, first language, country of residence, occupational status, and earnings.
“Predicted and observed general performance correlated substantially, providing a proxy measure of premorbid intelligence of comparable performance to common explicit tests such as the National Adult Reading Test,” the study stated.
What’s more, the academics also found that their intelligence estimates for individuals pre-illness indicated that those who contracted COVID-19 were actually likely to have had a “somewhat higher as opposed to lower cognitive ability” before they were sick.
After controlling for those factors, they found that those who had COVID-19 underperformed when compared to those who never contracted the disease.
The cognitive deficits were particularly pronounced for test tasks that involved reasoning, problem solving, spatial planning and target detection, while those who had COVID-19 fared better when they were asked to complete simpler tasks, such as working memory span and emotional processing.
“These results accord with reports of long-COVID, where ‘brain fog’, trouble concentrating and difficulty finding the correct words are common,” the authors noted. “Recovery from COVID-19 infection may be associated with particularly pronounced problems in aspects of higher cognitive or ‘executive’ function.”
The authors said their results appear to show that COVID-19 infection is associated with cognitive deficits that can persist into the recovery phase, such as in cases of long COVID in which symptoms can last for weeks or months after the initial illness.
The level of underperformance was also dependent on the severity of illness in the group who had COVID-19 during the pandemic. The study said those who had been placed on a ventilator during the pandemic exhibited the greatest cognitive deficits, so much so that it equated to a seven-point drop in IQ in a classic intelligence test.
The drop in intelligence among those who had been ventilated was also larger than the deficits observed in patients who had previously suffered a stroke or who reported learning disabilities, according to the paper.
The authors cautioned against drawing firm conclusions about the neurobiological or psychological basis for the intelligence deficits without brain imaging data; however, they said the results should serve as a clarion call for further research on the subject.
The study, “Cognitive deficits in people who have recovered from COVID-19,” was published in the journal The Lancet last week.