The fact that the virus could enter the brain is not surprising, as many viruses can cross the blood-brain barrier; however, neither is it good news. The SARS-CoV-2 virus has been shown, in controlled laboratory studies, to have the capability to cross the blood-brain barrier in mice.
This occurs through spike protein (the protruding arms or corona of the virus, called the S1 protein). These are visible in the picture below:
Brain fog
From the rodent studies it has been shown that the spike proteins can cause ‘brain fog’. There is no precise medical definition of brain fog. What it is intended to refer to is being absentminded or not particularly sharp and experiencing difficulty focusing. It can also refer to feeling sluggish when trying to think.
Issues with thinking and concentration have been reported by a number of people, post-coronavirus infection. Many have referred to this sensation as ‘brain fog’, despite the lack of any agreed medical interpretation.
S1 protein
It is the S1 protein that signals to the virus which cells the virus can enter. In addition, S1 proteins can independently cause damage by detaching from the virus and cause inflammation. In the human brain, this is probably through the release of cytokines (protein products secreted by certain cells of the immune system and have an effect on other cells) and inflammatory products.
In the research it was noted that the SRAS-CoV-2 S1 protein behaved very similarly to HIV, in terms of the outer protein crossing the blood-brain barrier and triggering a cytokine storm. Of specific concern to COVID-19 symptoms is where the coronavirus in the brain may target the respiratory centers of the brain and causing additional breathing problems at the time when the virus invades the cells of the lungs.
The research has been published in the journal Nature Neuroscience, where it is titled “The S1 protein of SARS-CoV-2 crosses the blood–brain barrier in mice.”
