Among the United Kingdom Biobank patients, researchers found out that COVID-19 may reduce the grey matter of the brain, particularly in areas of the brain that is involved in smell and memory processing. The study was published on March 7 in the journal Nature. The researchers looked at brain alterations in 785 UK Biobank people aged 51-81 years who had their brains scanned twice, including 401 cases who tested positive for COVID-19 between their two scans, with an average of 141 days between diagnosis and second scan.
Image-derived phenotypes (IDPs) were created and analysed with the use of brain scans. Each IDP represented a function or structure of the brain, according to News Medical. The cortical thickness and mean diffusivity were also measured by visualising the brain vertex-by-vertex and voxel-by-voxel. In addition, the Trail Making Test (TMT) was used to assess cognitive function. To eliminate confounding bias, the symptoms of respiratory illnesses such as pneumonia and influenza were assessed.
2,047 reproducible cerebral IDPs collected
There were a total of 2,047 reproducible cerebral IDPs collected, with 297 of them covering the olfactory area. The eight most prominent IDPs were related to the primary olfactory cortex in the cerebral cortex. The orbitofrontal cortex, anterior cingulate cortex, insula, ventral striatum, hippocampus, parahippocampal gyrus, and amygdala were among the areas where these significant IDPs overlapped. Furthermore, the major IDPs showed increased viral diffusivity, indicating functional connectivity with the temporal and frontal piriform cortices, anterior olfactory nucleus, and olfactory tubercle.
In COVID-19 patients, the remaining two prominent IDPs, which include the parahippocampal gyrus and the left lateral orbitofrontal cortex, had higher losses in cortical thickness and intensity contrast with time. The entorhinal and parahippocampal gyrus cortices both had substantial IDPs, but 90% of them were on the left side of the brain.
The greater decline in grey matter thickness and brain size
When compared, COVID-19 patients had a greater decline in grey matter thickness and brain size, as well as less contrast in orbitofrontal cortical tissues and the parahippocampal gyrus, according to News Medical. Furthermore, there was a decrease in whole brain volume and an increase in CSF fluid volume. A rise in brain atrophy and tissue damage caused these pathological alterations. In the meanwhile, between hospitalised and non-hospitalized COVID-19 patients, no significant brain alterations were identified.