As we age, there is typically a loss of gray matter of about 0.2% each year, which was seen in the control group. In contrast, the people with Covid in this study, at four months after their infection, had more gray matter loss than the control group, some up to tenfold more. Notably, the damage to the brain – the loss of gray matter – was chiefly in regions related to smell. Beyond the structural changes of the brain, there was a decline in the cognitive test among the infected group, taking longer to do the task. Separately, there was no difference in memory testing results between the two groups…

The mechanism for the structural brain changes is uncertain, but probably involves inflammation that originated from the nasal infection. Most studies of Covid and the brain support virus-induced inflammation, rather than direct infection of neurons, as the path to brain damage. The regions of the brain most affected in the Covid group are related to sense of smell, the limbic system, incriminating this nasal entry port. Whether the process is specific to this virus was examined in the current study by comparing Covid brain images with a small number of people with either influenza or pneumonia, and not seeing a similarity in pattern.