One of science's more mundane but useful services is to confirm what common sense and common experience suggest. At its most trivial, you get elaborate studies showing that good-looking people are better treated by strangers than are ugly people. Well, yes. But every once in a while, you get a study that confirms people's intuition about something important, like the relationship of madness and creativity.

Intuitively we know they are connected. We remember a crazy aunt who wrote poetry and the great artists who went mad or committed suicide. Indeed, the relationship is so well accepted that most of the debate is about the reason that craziness tends to genius and vice versa. But the assumption that one leads to the other is based on little more than anecdotal evidence.

Dr. Nancy Andreasen, a rigorous and prolific psychiatric researcher at the University of Iowa, has set out to attach numbers to the intuition. Over 15 years, she studied 30 faculty members of the University of Iowa Writers' Workshop. This is not quite the same creative league as, say, Nabokov or Pound or the authors on the average college English curriculum. But since most of history's creative heavyweights are dead and not available for psychiatric interview, Andreasen picked the next best sample.

She found an extremely high rate of mental illness in the writers, almost three times that of a control sample. Her most interesting finding, however, is counter-intuitive. We tend to think that genius is a blood relative of crazy thinking, the wild and bizarre kind that occurs in schizophrenia. The idea being that if you keep your visions and your voices under control, you produce a great novel; if they get out of control, you end up in the emergency room.

Andreasen found that this was not the case. Her creative writers were not prone to schizophrenia, which is a disorder of thinking. They were prone to manic-depression, which is a disorder of feeling. Manic-depressives experience uncontrollable mood swings from euphoric highs to the deepest despairing lows, which can additionally lead to alcoholism, a kind of self-treatment, or suicide, the most terrible self-treatment of all. What the Andreasen findings suggest is that creativity is related not to extraordinary modes of thinking but to extraordinary depths of feeling.

Related in a rather simple way. It is a question of degree. Up to a certain point, a six-octave range of feeling is a creative asset. Beyond that point, it is a catastrophe. For example, the high ("manic") phase of manic-depressive illness -- the euphoria, the rush of energy, the racing thoughts -- can initially be very creative. When I was practicing psychiatry, several of my manic patients refused treatment because they thrived on the creative rush and inexhaustible energy of the early phase of the manic attack.

Soon, however, they thrived no more. Creativity turned into craziness. At some point the engine revved up a little too much, the activity became too frenetic, and the thoughts flew so fast that they no longer connected. That's when the patient turned up at the hospital, brought in by a cop or a frantic relative.

In the individual patient it is not hard to see how thin is the line between creativity and gross disorganization. From society's point of view, this leads to a dilemma: there is a cost to curing madness. Were we to conquer manic-depressive illness the way we've conquered, say, polio and smallpox, we might find our culture diminished. The twinning of madness and genius is such that eradicating the one may have unintended but predictable effects on the other.

A most extraordinary example of this twinning occurred in a genius with a different mental ailment. Dostoyevsky was an epileptic. He described the pre-epileptic aura, the moments of suspension just before the onset of the seizure, as a flash of inner light and felicity, a sensation of indescribable bliss and serenity. In "The Possessed," Kirilov, an epileptic, says, "There are seconds -- they come five or six at a time -- when you suddenly feel the presence of the eternal harmony perfectly attained." Says Prince Myshkin (in "The Idiot") of the moment before his seizure, "I would give my whole life for this one instant."

To be sure, Dostoyevsky's pre-epileptic ecstasy is as rare as his genius. Nor will most manic-depressives qualify for the faculty of the Iowa Writers' Workshop. But Andreasen's demonstration that illness may sometimes be allied with genius is a comfort of sorts. Anything that makes suffering a bit less pointless must count as good news.