Researchers found the spike protein inside the cerebral arteries, which flow to the brain. The study confirmed that, in all of the patients, some of the spike protein detected originated from the COVID-19 vaccines.

https://childrenshealthdefense.org/defender/spike-protein-found-female-stroke-victims-17-months-mrna-covid-vaccine/?

AND

Expression of SARS-CoV-2 spike protein in cerebral Arteries: Implications for hemorrhagic stroke Post-mRNA vaccination

https://www.sciencedirect.com/science/article/pii/S096758682500195X