In 1997, when she was 44, a massive stroke cost painter Katherine Sherwood the permanent use of her right hand.
Today, the Bay Area artist is painting with her left hand, her career more successful than ever.
Back in 1980, an aneurysm from a previously undiagnosed brain abnormality required surgery that completely wiped out noted jazz guitarist Pat Martino's musical memory. Surgeons told him he had been two hours away from death, put him to sleep, and removed 60 percent of his left temporal lobe.
Playing with a computer and listening to his old recordings, Martino, who lives in South Philadelphia, taught himself to play again and has made more than a dozen albums. In 2004 he won the Downbeat magazine readers poll as "Guitarist of the Year."
"Miraculous" artistic recoveries such as these have been noted over the years, as have examples of artists creating great work while suffering from some form of irreversible brain trauma. Composer Maurice Ravel, for example, is thought to have written his best-known work, Bolero, while suffering from the degenerative brain disease known as FTD, or frontotemporal dementia.
But with the aid of new diagnostic instruments, neurologists and other scientists hope to unlock the secrets of creativity both in artists and the general population.
Anjan Chatterjee, a neurologist at the University of Pennsylvania, says that while brain injuries and disease usually hamper the production of art, the exceptions could be revealing. "Sometimes," he says, "the great artist can give us insight into the process because they have distilled it into a more extreme version."
Using a technique called fMRI, or functional Magnetic Resonance Imaging, scientists can measure changes in the brain while a person engages in creating art or any form of mental activity. The technique was invented in the mid-1990s, but "it's only in the last few years that it has taken off," Chatterjee says.
So it is an infant science with anecdotal information preceding scientific studies and questions far outnumbering answers.
But the implications are vast. Unlocking the secrets of creativity, scientists say, could result in everything from improvements in helping stroke victims recover to developing new teaching methods.
To take an example that might seem unlikely, Chatterjee cites a situation in which creativity can be the key to survival: Army Special Forces soldiers dropped behind enemy lines and needing to improvise to survive.
"People are creative in different ways," says Chatterjee, himself a serious photographer. "For example, the kind of creativity that operates in the visual arts might be different from the creativity that operates in mathematics. We are at the beginning of understanding the physiology of why certain sensations give us pleasure and the neural underpinnings of aesthetic experiences.
"There are two ways to approach this," he adds. "What is the brain teaching us about creativity and what is creativity teaching us about the brain?"
Robert Zatorre, a neuropsychologist at McGill University in Montreal, adds that "we might be able to make predictions about who can benefit from what kinds of training. Who has a super aptitude."
However, he adds a cautionary note: "Everyone's brain is different, which is a damned good thing. Otherwise it would be a pretty boring world."
Chatterjee never treated Katherine Sherwood as a patient, but as he studied the places where neurology and art intersect, he became fascinated by her recovery, and has become a friend and admirer. "For me," he wrote in an article for a 2008 exhibition catalog of her paintings, "artists like Sherwood who have the resilience to continue to produce a body of work after brain damage are of great interest."
"One might ask, as I do, what might have happened to Sherwood's brain as it changed following her stroke that 'accounts' for her current artistic style."
Before the stroke, her work was controlled, intellectual, and filled with esoteric images. For example, Aldrich Ames, named for a CIA officer convicted of spying for the Soviet Union, contains a fragment of the U.S. flag against a background of CIA satellite photos of nuclear test sites in Russia.
Her later work - she cannot control her left hand as well as she did her right - tends to be less intricate and more abstract. Much of it - such as One in 100 Billion - is based on neurons and brain imagery, which has fascinated her since she saw her own brain angiogram, an X-ray image of cerebral blood vessels. She also makes frequent use of symbols from "The Lesser Key of Solomon," an anonymous 17th-century mystic tract.
Sherwood says that she doesn't necessarily buy into the critical consensus that her work after the stroke is more powerful than before. But she knows that she feels different in creating it.
"My left-handed painting is less intellectualized, more spontaneous," she says by telephone from the University of California, Berkeley, where she is on the faculty.
"I do everything, more slowly, and I think my paintings are served well by that slowing down."
Relaxing in his South Philadelphia apartment, Martino reported a somewhat similar experience when he is soloing. He says that while the stroke has deprived him of some memory, it also helped his music in unforeseen ways: "The greatest gift was the ability to focus on the moment, the moment when you can't see a past and a future," he said. "The less control, the better."
In fact, Georgia Tech neuroscientist Paul Corballis has theorized that brain injuries can in some cases help free the mind to be more open and creative, particularly in cases where the injury harms linguistic ability. (Sherwood speaks more slowly than she did before her stroke.)
"Language is the bully of the brain," he says. "It takes up its own space and if something else gets crowded out, too bad."
Corballis says there are limits to what fMRIs can study at the moment because the subject can't move around. While fMRIs remain a key tool, other medical techniques are being brought into play.
Corballis has worked with subjects who have had a surgical procedure used in extremely severe cases of epilepsy, an operation that virtually divides the brain. "It's almost like having two brains in one head," he says, allowing him to see the left hemisphere, commonly associated with language and logic, functioning almost independently of the right hemisphere.
He also cites the work of Allan Snyder, an optical physicist who heads the Centre for the Mind in Sydney, Australia. Using transcranial magnetic stimulation (TMS), a technique associated with treating Parkinson's and other disorders, Snyder says he has produced heightened mental functioning in his subjects for short periods of time by depressing - rather than stimulating - certain areas of the brain.
But it remains a science where questions are still being developed rather than answered, Corballis says.
"We're where chemistry was in 1870, before the periodic table," he says. "Or maybe where physics was pre-Einstein."