Always Look on the Bright Side of Life

and you won't go senile, at least according to a recent study that examined scores on a personality test (the Minnesota Multiphasic Personality Inventory) then looked for evidence of demential 40 years later.

This is interesting but I'd urge several cautions
1. Diagnosis of dementia was based on interviews of patients and/or families. Maybe people are more likely to label cranky old relatives as demented than optimistic ones
2. Maybe the pessimism seen earlier in life is a manifestation of underlying factors that also cause early dementia (i.e. the study shows correlation not causation).

I think this quote, by the leader of the research, gets it wrong:

"Certainly the last thing you want to do is to say, 'Well, I am a pessimist; thus, I am doomed to develop dementia 20 or 30 years later,’ because this may end up becoming a self-fulfilling prophecy.”

I think the study would tend to reinforce pessimism, not necessarily drive dementia.