The covid-19 infection has caused many deaths, arousing scientific interest worldwide. Different studies show changes in the brain due to the virus in post-mortem analyses carried out where indications of the presence of viruses in the central nervous system were found.

When analyzing the behavior of the Alpha strain of the virus in different subjects, it has been concluded that the total of the patients analyzed presented alteration of taste and 86% of smell partially. The brain regions responsible for the olfactory system are the parahippocampal gyrus, the piriform cortex, the orbitofrontal areas, and the entorhinal cortex.

Brain imaging and artificial intelligence are widely explored tools to observe structural changes or abnormalities in the brain in vivo. The Gwenaelle Douaud 2022 et. al. study uses Longitudinal brain magnetic resonance imaging from the UK Biobank database, where 785 subjects from 51 to 81 years old were selected, 401 cases with two samples (before and after COVID infection) images with an approximate separation time of 141 days. The remaining 384 cases were control subjects.

The main focuses of this study were to analyze the thickness of the gray matter, the tissue contrast between the regions of interest, and volumetric analysis of the whole brain between the two groups of subjects.

Among the results obtained, it was found that for the Alpha variant of SARS-Cov-2, brain changes were observed mainly in the limbic and olfactory cortical system, where significant differences in the diffusion measures responsible for measuring tissue damage were found. The regions that are connected to the piriform cortex, the olfactory nucleus, and the tubercle showed changes of 0.7% on average. Moreover, the volume, thickness, and contrast of the perirhinal, parahippocampal, and entorhinal cortex, showed a variation from 1.3 to 18% against the control group. Also, a significant cognitive decline was observed in the SARS-Cov-2 positive group caused by atrophy of the Crus II region of the cerebellum. Is important to note that there was an increase in cerebrospinal fluid volume, which is expected when there is a reduction in gray matter in the brain.

On the other hand, the parahippocampal gyrus is responsible for short-term memory and is connected to the entorhinal and piriform cortexes responsible for primary olfactory functions. The connections of the orbitofrontal cortex and the anterior olfactory nucleus were also affected. It was evidenced that in the subjects with the virus, the brain diffusivity metrics of the control group changed.

The results show that the affected regions of the limbic system of the brain can be caused by the spread of the disease through the airways. One of the study’s limitations is that it cannot be differentiated whether the subjects diagnosed with COVID 19 are due to an infection or vaccination by the type of tests used. On the other hand, from the date of the study until today, other new variants of the virus have been found that have drastically reduced the symptoms of loss of taste and smell. For instance, in the presence of the Omicron variant, neurodegeneration may change or not exist.