Covid leading to loss of grey matter, hits cognition: Study

THE RESEARCHERS STUDIED PRE AND POST-INFECTION BRAIN SCANS OF CLOSE TO 800 PEOPLE IN THE UK

NEW DELHI: Covid-19, even if mild or moderate, is possibly leaving people with significant impact on their brains, according to a study involving pre- and post-infection brain scans involving close to 800 people in a study carried out in the UK.

The scans showed loss of grey matter, indicative of damage, and the areas affected involved functions relating to smell and taste, cognition and memory formation. Most of the patients examined had mild-to-moderate disease.

“We identified significant effects of Covid-19 in the brain with a loss of grey matter in the left parahippocampal gyrus, the left lateral orbitofrontal cortex and the left insula. When looking over the entire cortical surface, these results extended to the anterior cingulate cortex, supramarginal gyrus and temporal pole,” said the researchers, who work with the University of Oxford, in their report on medRxiv, which is yet to be peer-reviewed.

The study was conducted after the researchers pored over data of 40,000 people in the UK Biobank, a long-term, large scale repository of biomedical data, and reached out to volunteers.

In all, 782 people who previously underwent brain scans participated, and of these, 394 subsequently tested positive for SarsCov-2.

The researchers used the scans of these people from before their infection and carried out new scans afterwards. They compared both these scans, as well as the change they saw with the control group — the remaining people who did not have Covid-19 between the two sets of scans.

“In total, 394 Covid-19 patients with usable imaging data at both timepoints were included in this study, as well as 388 controls, matched for age, sex, ethnicity and time elapsed between the two scans. These large numbers may allow us to detect subtle, but consistently spatially distributed sites of damage caused by the disease, thus underlining in vivo the possible spreading pathways of the virus within the brain,” the authors said.

The authors said they found three main regions that showed significant loss of grey matter, in both thickness as well as volume: the parahippocampal gyrus, the lateral orbitofrontal cortex, and the superior insula. All of these were localised to the left hemisphere of the brain.

The parahippocampal gyrus plays an important role in spatial memory and navigation; the orbitofrontal cortex is believed to play a role in higher-order cognition such as decision-making, and the superior insula is part of a region that is yet to be fully understood but is believed to play a role in processing some sensory inputs and emotions.

“The loss of grey matter in areas of brain linked to taste and smell is consistent with the clinical symptoms of the patients; loss of taste and smell is one of the earliest symptoms in many Covid-19 patients and it is one of the most sensitive markers of infection,” said Dr Rajinder K Dhamija, head of the department of neurology at Lady Hardinge Medical College.

“One of our studies had proposed that there were two mechanisms that the virus could be using to affect the brain --- either getting in directly through the olfactory mucosa (the inner lining in the nasal cavity) or forming tiny clots in the epithelial layer of the blood vessels in the brain. The examination of the pre and post-Covid-19 scans seems to support the first hypothesis... but we still need further studies to understand what it means for the Covid-19 patients. Grey matter once destroyed cannot be created, but patients do get back their sense of smell and taste in four to six weeks,” he added.

The researchers found that similar neurological features were seen in a small group of 15 people who were hospitalised. “Comparing the few patients who had been hospitalised with Covid-19 with those who had not also showed a similar pattern of olfactory- and memory-related brain regions, particularly centred around the left cingulate cortex, and the right hippocampus and amygdale [as being affected],” they said.