The website here is unfortunately, non-English, but if you click on the links on the bottom (the ones with blinking blue >>) you will see the pdf files you can use to construct your own paper brain.
Another 3D paper brain can be made using pdf files that can be found here.
Let's also not forget the famous brain hat by Ellen McHenry here.
For the younger set, five messy ways to play brain surgery here.
This one is a kitchen utensil no neuropsychologist should be without. Particularly good with off-white jellies, such as almond pudding. You could also consider putting some frozen strawberries inside to simulate a tasty bleed.