There is no sound evidence of having so much microplastics in the brain. The studies that show it are very broad, incomplete and did not check for false positives.
"The main analytical method used in this study was pyrolysis gas chromatography-mass spectrometry. This method can give false results when used to measure plastics because fats (which the brain is mainly made of) give the same pyrolysis products as polyethylene (the main plastic reported)"
And then you have something like this: pubmed.ncbi.nlm.nih.gov/32882126
"The main analytical method used in this study was pyrolysis gas chromatography-mass spectrometry. This method can give false results when used to measure plastics because fats (which the brain is mainly made of) give the same pyrolysis products as polyethylene (the main plastic reported)"
And then you have something like this: pubmed.ncbi.nlm.nih.gov/32882126