An analysis of brain scans of participants in the UK Biobank has shown there are significant differences between the condition of the brain before and after mild COVID-19 infection. These included a reduction in overall brain size, reduction in grey matter thickness in the orbitofrontal cortex and hippocampal gyrus, and changes in markers of tissue damage in regions functionally connected to the primary olfactory cortex. Infected participants also showed, on average, a larger cognitive decline than participants who had not contracted COVID-19.