PSYPOST
Difficulties with cognitive functions or skills, such as the ability to recall memories, concentrate on tasks, or find the right words in conversation, are commonly reported following a COVID infection. These symptoms are often referred to as “brain fog”, and are especially common among people who have long-term or persistent symptoms called long COVID.
At the latest count in March 2023, there were 1 million people in the UK with long COVID who reported difficulty concentrating, and three-quarters of a million who reported memory loss or confusion.
In the short term, brain fog symptoms can affect people’s ability to carry out their normal daily tasks, such as work and childcare, and reduce their quality of life.
In the longer term, mild cognitive impairment can develop into more severe conditions, such as dementia. COVID infection generally has been linked to an increased risk of being diagnosed with dementia.
So to support people in the short and longer term, it’s important to understand the nature, size and duration of the effects of brain fog and long COVID more generally on cognitive function.
In a new study, my colleagues and I set out to understand whether a COVID infection, and symptom duration, affected performance in cognitive tests, and how test performance changed over time. We found people with persistent symptoms fared worse in these tests up to two years after a COVID infection.
Brain training
To test cognitive skills, we invited participants in the COVID Symptom Study Biobank to complete a series of 12 brain-training-style tasks online in July 2021 and again in April 2022. In the first round, more than 3,300 people completed the test. Another 2,400 completed the second round, of whom 1,700 had also participated in the first round.
The COVID Symptom Study Biobank is a study that began in 2020, recruiting people from the COVID Symptom Study smartphone app (now the ZOE Health Study) which tracks symptoms and COVID tests. The study includes over 8,000 people both with and without a history of COVID infection and with a range of shorter- and longer-term COVID symptoms.
The tasks aimed to cover a range of elements of brain function, including visual memory, attention, verbal reasoning and motor control. Some tasks involved remembering words and shapes after a short delay of less than a minute, or a longer delay of around 20 minutes.
Other tasks included watching sequences of numbers appear on the screen and then repeating the sequences, clicking on a moving “bullseye” target, and deciding if pairs of words have the same meaning. Similar versions of the test are available for anyone to try online.
We then recorded how accurately people completed the tasks and their response times.
What we found
When we compared how accurately people with or without a history of COVID completed the test in the first round, we saw that people with an infection had lower scores on average across the 12 tasks.
Digging deeper, we saw that the effect of COVID on test performance was biggest for people with a longer symptom duration of more than three months. These people meet the criteria for having long COVID.
