I came across this test recently. If you need to discover a Russian under-cover agent you can show them color words (words like red, green, blue) colored in a different color.
Green Blue Purple
If you comprehend the words, you perform poorly at this test than otherwise.
The Stroop test on Wikipedia.
I first encountered the story of Phineas Gage in my freshman year in college. Phineas had a projectile drill a hole in his head (while he worked the railroad) and he survived the incident. The incident caused a massive personality change in Phineas and conclusively ruled out phrenology as a reasonable model of how the brain worked.
After the incident Phineas’ life comprised a trip to South America, a gig at P.T. Barnum’s establishment and a massive change in our understanding of the brain. This wikipedia article covers a good chunk of this work.