It has been suggested that madness and genius have a common source. When the brain processes stimuli, it "learns" to discard information that it considers irrelevant.
For some unknown reason, some people doesn't develop these inhibitors and the brain is more "open" for input, which other peoples brains might observe, but discard as irrelevant.
These people are frequently called "creative", as they can observe things, where others can not (e.g. artists etc.).
In extreme cases, the information becomes overwhelming and a high intelligence is required to process the information. These people are able to utilize input in ways most other people can't. These are often referred to as "geniuses" (e.g. Einstein etc.).
If a person lacks inhibitors and the intelligence to process it, they succumb to "madness" (i.e. they tend to lose their grip on reality)
Sometimes people starts out with low inhibitors and high intelligence, but eventually the mind tires, intelligent or not, and madness sets in after a period of brilliance.
Interesting field of researh, but I'm currently too lazy to look up the links for the source...