Below is the URL for the online version of a short article from
the current issue of "Discover" magazine, describing a case
of sudden onset of dementia (in a long-term vegetarian) that was
(partially) alleviated by vitamin B-12 injections:

http://www.discover.com/feb_00/featdementia.html

[Note: the article has an error - the last few paragraphs are
repeated.]

I would mention here that while researching vitamin B-12 (some time
ago),
I did review a few papers and abstracts discussing the possibility
of a causal linkage between vitamin B-12 deficiency and dementia.
The topic is controversial, in that papers can be found that argue
both sides of the issue.

The article above is quite interesting and I encourage all to read it.

Tom Billings
http://www.beyondveg.com