Despite its moniker, mental illness often has a biological component. Some researchers suspect it has to do with a person's inability to shut out stimuli. Selectively ignoring certain incoming sights, sounds and thoughts is a hallmark of the mentally healthy, a trait psychologists call "latent inhibition." For example, a study of nearly 200,000 20-year-old Finnish males found those with higher intelligence were more than 12 times more likely to develop bipolar disorder as they aged. The link, surmised researchers, was the capability to rapidly process information while problem-solving, a hyper-alertness thought to accompany some types of mental illnesses [source: Collingwood]. Turns out, the selective hearing your child or spouse develops when it is time to take out the trash may be a good thing.
On the other hand, biology could be behind a person's propensity for certain mental maladies. For example, researchers have discovered nerve cells in a portion of the brain called the posterior cingulate cortex become more active when monkeys explore potentially rewarding new courses of behavior instead of the normal routines. It is suspected that for people who have an obsessive-compulsive disorder compelling them to adhere to strict behavioral patterns, the flexibility to pursue new -- even potentially gratifying -- avenues is absent [source: Futurity].
And then there are those who defy their diseases. Although Tesla exhibited behaviors consistent with obsessive-compulsive disorder, his thought process was agile. Just as engineers now use computer models to construct a complicated apparatus, Tesla virtually tested and recalibrated every invention before ever building a single prototype. Only he did it entirely in his own mind!
Tesla's autobiography, in which he described his creative process, reveals that across hundreds of inventions, he never built a device that didn't work as he thought it would [source: Knapp]. The link between intelligence and mental illness -- even if we don't fully understand it -- often seems to be two sides of the same coin.