Medicine has suspected a link between madness and creativity for centuries. Artist Vincent Van Gogh provided ample anecdotal evidence when he lopped off the lower lobe of his left ear in 1888 and gift wrapped it for a prostitute he loved. Author Ernest Hemingway, long plagued by depression, may have done the same when he took his own life with a shotgun in 1961. These cases provide insight into the dynamic relationship between mental illness and creativity, but no rational explanation.
The explanation may lie in a condition shared by highly creative people and those with hallucinatory mental illnesses like schizophrenia -- low latent inhibition (LI). Each of us is constantly assaulted with sensory information; that raw data which Snyder believes autistic savants have trouble converting into mindsets. Humans and other primates have evolved enough to weed through this information and consider only what we need to survive, to perform a necessary task or to consider data we haven't already catalogued. The other information is unconsciously discarded, filtered through the process of latent inhibition. It's why we tend not to latch onto the constant buzzing of fluorescent lights overhead or compile snippets of conversations in crowded restaurants into a senseless whole.
A low level of latent inhibition has been shown in schizophrenics [source: Weickert, et al]. Because they can't distinguish between external and internal stimuli (for example, voices), schizophrenics attach meaning to the sensory input people with normal latent inhibition unconsciously ignore [source: Carson].
Harvard psychologist Dr. Shelley Carson found that highly creative people also experience a lower LI threshold. What creative people do with the additional stimuli appears to be the separation between creativity and insanity. In a 2004 study, Carson found that test subjects with low latent inhibition coupled with a relatively high IQ (120 to 130) also had creative abilities. Carson postulated that people with high intellects aren't assaulted by the additional information allowed into their consciousnesses through low LI like schizophrenics are. Instead, they make creative use of it: "Intelligence allows you to manipulate the additional stimuli in novel ways without being overwhelmed by them" [source: Carson].
The implication of this is, of course, that schizophrenics simply have lower intellects than highly creative people. Each group teeters on opposite sides of the same raging river of information and stimuli, holding ground only through their respective intelligence levels. While this may be an obvious conclusion, the exception that disproves the rule (schizophrenics who maintain a high intellect) doesn't support it. Studies have found a decline in intellect among some schizophrenics; but others show no decline -- remaining either at the same high or low intelligence quotient they possessed prior to developing the mental disorder (which appears on average at age 16 for males and 20 for females) [source: Weickert, et al, Carson].
If it isn't intellect that separates genius from insanity in the human brain, then what does? Science simply doesn't know yet; what constitutes that blurry line remains a mystery. Perhaps it will be Snyder's forays into the skulls of his test participants using the thinking cap that will finally force the brain to give up its secrets.