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Brain Imaging Before and After Covid-19


This is an abstract taken from a pre-print, and therefore not yet peer reviewed, paper "Brain imaging before and after COVID-19 in UK Biobank" by Douaud et al. The research is based at the Wellcome Centre for Integrative Neuroimaging, Nuffield Department of Clinical Neurosciences, University of Oxford, UK.


Quick Rose Cottage Doc Summary:

  • 40,000 Patient's brains were scanned pre pandemic

  • 782 were then rescanned - 394 of these had tested positive for Covid-19

  • There was loss of grey matter of the brain in those who had had Covid-19

  • The areas were: the left parahippocampal gyrus, the left lateral orbitofrontal cortex and the left insula

  • There was NO difference between those who were hospitalised and those that were not.

  • The areas of loss are in the limbic area of the brain close to the olfactory and gustatory pathways.

  • The left parahippocampal gyrus plays an important role in memory encoding and retrieval (ie remembering events).

  • The left orbitofrontal cortex it is hypothesized to play a role in higher-order cognition like decision-making, rational thought, reasoning, and even the full expression of personality.

  • The left insula is involved with empathy and social cognition.

  • The limbic nature of the regions of the olfactory system, and their physical proximity to the hippocampus in particular, raise the possibility that longer-term consequences of SARS-CoV-2 infection (for which some suggest that the coronavirus itself enters the brain via the olfactory route) might in time contribute to Alzheimer’s disease or other forms of dementia.


Abstract

There is strong evidence for brain-related pathologies in COVID-19, some of which could be a consequence of viral neurotropism ( the ability of the SARS-CoV-2 virus to invade and live in neural tissue - brains, nerves etc).

The vast majority of brain imaging studies so far have focused on qualitative, gross pathology of moderate to severe cases, often carried out on hospitalised patients.

It remains unknown however whether the impact of COVID-19 can be detected in milder cases, in a quantitative and automated manner, and whether this can reveal a possible mechanism for the spread of the disease.

UK Biobank scanned over 40,000 participants before the start of the COVID-19 pandemic, making it possible to invite back in 2021 hundreds of previously-imaged participants for a second imaging visit. Here, we studied the effects of the disease in the brain using multimodal data from 782 participants from the UK Biobank COVID-19 re-imaging study, with 394 participants having tested positive for SARS-CoV-2 infection between their two scans.

We used structural and functional brain scans from before and after infection, to compare longitudinal brain changes between these 394 COVID-19 patients and 388 controls who were matched for age, sex, ethnicity and interval between scans.


We identified significant effects of COVID-19 in the brain with a loss of grey matter in 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. We further compared COVID-19 patients who had been hospitalised (n=15) with those who had not (n=379), and while results were not significant, we found comparatively similar findings to the COVID-19 vs control group comparison, with, in addition, a greater loss of grey matter in the cingulate cortex, central nucleus of the amygdala and hippocampal cornu ammonis (all |Z|>3).

Our findings thus consistently relate to loss of grey matter in limbic cortical areas directly linked to the primary olfactory and gustatory system.

Unlike in post hoc disease studies, the availability of pre-infection imaging data helps avoid the danger of pre-existing risk factors or clinical conditions being mis-interpreted as disease effects. Since a possible entry point of the virus to the central nervous system might be via the olfactory mucosa and the olfactory bulb, these brain imaging results might be the in vivo hallmark of the spread of the disease (or the virus itself) via olfactory and gustatory pathways.


Reference

The whole paper can be read here:

https://www.medrxiv.org/content/10.1101/2021.06.11.21258690v1.full-text

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