A study of more than 84,500 people backs prior indications that surviving the novel coronavirus may be associated with potentially serious cognitive deficits, Reuters reported on Tuesday. While the new study, which is based on an online survey, has some major limitations, other research has found that covid-19 can cause neurological issues even in people with mild cases.
The research team, led by Imperial College London’s Adam Hampshire, reviewed data from the Great British Intelligence Test—a collaborative project with BBC2 Horizon that collects a broad array of cognitive test and questionnaire data. It was expanded to include questions about covid-19 infection in May; in the dataset of about 84,500 people, 9,201 reported infections without respiratory symptoms; 3,466 had respiratory difficulties but did not obtain medical assistance; 176 required medical attention at home; 147 were hospitalized; and another 60 had to go on a ventilator.
“People who had recovered, including those no longer reporting symptoms, exhibited significant cognitive deficits when controlling for age, gender, education level, income, racial-ethnic group and pre-existing medical disorders,” the researchers wrote in the study. “They were of substantial effect size for people who had been hospitalised, but also for mild but biologically confirmed cases who reported no breathing difficulty.”
The GBIT is an online survey that has respondents answer a variety of questions about their life situation as well as complete tasks designed to measure their abilities in semantic problem solving, spatial working memory, selective attention, and emotional processing. Those results are in turn used to assess overall cognitive scores of a population. In this study, the researchers did not have before-and-after data for respondents who said they had been ill with the coronavirus. Instead, they calculated how many standard deviations their cognitive scores were from healthy controls, accounting for factors like age, gender, education, income, racial-ethnic group, and pre-existing medical conditions.
The researchers wrote that the survey results indicated the cognitive deficits were correlated with the degree of medical attention received, a proxy for the severity of each case. The hardest hit were those who were hospitalized and required the user of a respirator, whose GBIT global composite scores were “equivalent to the average 10-year decline in global performance between the ages of 20 to 70 within this dataset” and larger than the mean deficit of those who had reported having a stroke or learning disability.
The “deficits were broad, affecting multiple cognitive domains,” the researchers added, though they were most apparent in “semantic problem solving and visual selective attention whilst sparing tests of simpler functions such as emotional processing and working-memory span.”
That said, there are some major caveats here. The study was not peer reviewed and relied on online questionnaires and tests, and experts told Reuters its design was inherently limited. In particular, the observed effects may not persist long-term.
Joanna Wardlaw, an applied neuroimaging professor at Edinburgh University, told Reuters: “The cognitive function of the participants was not known pre-COVID, and the results also do not reflect long-term recovery—so any effects on cognition may be short term.” University College London medical imaging science professor Derek Hill told the news agency the results did not contain before-and-after scores, and the vast majority of those who said they had fallen ill with coronavirus did not report testing positive for it, meaning many may have self-diagnosed. (However, testing positive for the virus was associated with worse outcomes in the GBIT, even among those with mild cases.) Hill said the study was an “intriguing but inconclusive piece of research into the effect of COVID on the brain,” adding that long-term research is needed to understand whether this brain damage is permanent.
This study adds to a body of knowledge suggesting that the SARS-CoV-2 virus can cause neurological damage. Some patients have reported loss of smell or taste (in rare cases perhaps permanently), and medical research published this year found evidence of neurological complications ranging from cognitive impairment or delirium to swelling and hemorrhaging in the brain in a small number of patients. Scientists suspect that cytokine storms, in which the body’s immune system attacks its own cells indiscriminately, may be one cause of damage to the neurological system and the heart.
Such observations wouldn’t be unprecedented. Medical researchers have observed surges of neuropsychiatric symptoms in past viral pandemics. In a study published earlier this year, University of California San Diego scientists argued that a potential wave of neurological illness caused by the pandemic will require long-term attentiveness by the medical community.
“We also want people to be aware that the nervous system could be involved in COVID-19, so we hope people will talk to their physicians about any emotional, behavioral, cognitive, or sensorimotor symptoms they might have over the course of their recovery,” lead author Emily Troyer, a UCSD psychiatrist, told Gizmodo at the time. “We don’t want to cause people more worry—we just want people to know to talk to their healthcare providers about these kinds of symptoms if they arise, and together we will get through this.”