As the neurologist
Oliver Sacks points out, sometimes we get the most valuable insights into the mind when the mind is damaged.
I've just been reading about
Phineas Gage again, the guy who had a pole dynamited through his head and survived (but as a different person).
And the story of
Clive Wearing is pretty tragic - for over 20 years he has had a seven second memory. (
More, and
more.)