“This preliminary study examines whether daily CBD dose of 15-25 mg/kg produces cerebral macrostructure changes and, if present, how they relate to changes in seizure frequency.

In conclusion, short-term exposure to highly purified CBD may not affect cortical macrostructure.”

https://www.ncbi.nlm.nih.gov/pubmed/32322816

“We document no effect of CBD on gray matter volume and cortical thickness.”

https://www.sciencedirect.com/science/article/pii/S258998641930111X?via%3Dihub