Leonardo da Vinci's legendary struggles to complete projects suggest he may have had attention-deficit hyperactivity disorder (ADHD), a British researcher says.
That's the latest in a series of attempts to understand the genius and work habits of an inventor and artist often considered the most creative person ever known.
The fascination with da Vinci dovetails with the 500th anniversary of his death earlier this month.
In the latest theory, Marco Catani of King's College London said ADHD may have been a factor in da Vinci's chronic procrastination as well as his exceptional achievements. Catani's theory is based on historical accounts of da Vinci's work habits and behavior.
"While impossible to make a post-mortem diagnosis for someone who lived 500 years ago, I am confident that ADHD is the most convincing and scientifically plausible hypothesis to explain Leonardo's difficulty in finishing his works," said Catani, a professor of forensic and neurodevelopmental science.
"Historical records show Leonardo spent excessive time planning projects but lacked perseverance. ADHD could explain aspects of Leonardo's temperament and his strange mercurial genius," Catani explained in a college news release.
The inability to complete tasks was seen in da Vinci from childhood.
The artist was always on the go, often switching from project to project, and he worked around the clock by taking short naps, according to Catani, who specializes in treatment of conditions such as ADHD and autism.
Along with being left-handed, da Vinci was likely dyslexic and to have a dominance for language on the right side of his brain, Catani said. All are common in people with ADHD.
"There is a prevailing misconception that ADHD is typical of misbehaving children with low intelligence, destined for a troubled life," Catani said. "On the contrary, most of the adults I see in my clinic report having been bright, intuitive children but develop symptoms of anxiety and depression later in life for having failed to achieve their potential."
Catani said da Vinci considered himself a failure.
"I hope that the case of Leonardo shows that ADHD is not linked to low IQ or lack of creativity but rather the difficulty of capitalizing on natural talents," he said. "I hope that Leonardo's legacy can help us to change some of the stigma around ADHD."
The study was outlined in a paper published May 23 in the journal Brain.
Earlier this month, Dr. Salvatore Mangione, of Thomas Jefferson University in Philadelphia, said dyslexia was probably behind da Vinci's genius. Like ADHD, dyslexia does not affect intelligence, and research suggests people with the condition may be highly creative.
In an article in The American Journal of Medicine, Mangione noted da Vinci was an atrocious speller -- a sure sign of dyslexia.
Other recent research suggests da Vinci may have had an eye problem called strabismus, which makes 3D vision impossible. Having 2D vision is associated with dyslexia and skill in visual art, Mangione said.
The U.S. National Institute of Mental Health has more on ADHD.