An analysis of brain scans from people once infected with COVID-19 suggest a consistent pattern in loss of grey matter over time, say researchers.

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The researchers affiliated with the University of Oxford posted findings ahead of peer review to medRxiv, drawing on data from the UK Biobank. "Our findings thus consistently relate to the loss of grey matter in limbic cortical areas directly linked to the primary olfactory and gustatory system", or areas in the brain related to the perception of smell and taste, the authors wrote. The team compared brain scans taken pre-pandemic to scans taken about three years later among 394 Covid-19 patients and 388 matched controls, reports Fox News.

Further analysis included 15 hospitalised patients compared with 379 people who had not been hospitalised. The initial set of scans taken before the pandemic strengthens the findings, the researchers said, because they help differentiate the effects of COVID-19 disease from patients' preexisting health conditions. The team said the three areas revealing a "significant loss" in thickness and volume of grey matter among COVID-19 patients was the "parahippocampal gyrus, the lateral orbitofrontal cortex and the superior insula", later adding that the "strongest deleterious effects of COVID-19 could be seen predominantly in the left hemisphere".

The results from the comparison of hospitalised patients "were not significant", but authors noted "comparatively similar" findings to the larger group of COVID-19 patients, "with, in addition, a greater loss of grey matter in the cingulate cortex, central nucleus of the amygdala and hippocampal cornu ammonia". The team stopped short of pinning a causal relationship due to the study design, yet still expressed confidence in the results. "By using automated, objective and quantitative methods, we were able to uncover a consistent spatial pattern of loss of grey matter in limbic brain regions forming an olfactory and gustatory network", the team said.

"Whether these abnormal changes are the hallmark of the spread of the disease (or the virus itself) in the brain, which may prefigure a future vulnerability of the limbic system, including memory, for these patients, remains to be investigated", they added.