As an artist, mathematician, and inventor, Leonardo da Vinci was without doubt a master. But "his contemporaries could never understand or forgive his lack of discipline," write researchers in the journal Brain. Indeed, as da Vinci jumped from task to task, he left plenty of works unfinished—even his famed Mona Lisa, per CNN. But to accuse him of a lack of discipline is too simplistic, says Marco Catani, a professor of neuroanatomy and psychiatry at King's College London. Instead, he thinks it's likely that da Vinci had attention deficit and hyperactivity disorder. Catani says historical evidence shows da Vinci would switch between tasks, work through the night, and rely on short naps—signs of the procrastination and restlessness that can come with ADHD. Others have argued the left-handed da Vinci had dyslexia, based on spelling errors and mirrored writing.
Both dyslexia and left-handedness are common among people with ADHD, as is "atypical hemispheric dominance." As da Vinci retained a language ability after a left-hemisphere stroke, Catani believes he had a "reverse right hemisphere dominance for language," found in less than 5% of people. "I am confident that ADHD is the most convincing and scientifically plausible hypothesis," says Catani, per Eureka Alert. He was left wondering "what would have been the impact of his work on history if he had managed to apply himself more consistently to his art and effectively disseminate his intuitions and discoveries." But others say ADHD might actually explain da Vinci's achievements. People with ADHD can "focus intensely … on a narrow area" and "intensify creativity," a rep for the Royal College of Psychiatrists tells CNN. (Da Vinci might've also had an eye disorder.)