WASHINGTON — A longtime smoker, a patient code-named Nathan simply forgot his two pack-a-day addiction after a stroke.

He had no cravings, no desire to quit. “My body forgot the urge to smoke,” he told his doctor nonchalantly.

His comment inspired research that suggests damage to a silver dollar-sized spot deep in the brain can wipe out the urge to smoke. The surprising discovery may shed important new light on addiction.

“The quitting is like a light switch that went off,” said Dr. Antoine Bechara of the University of Southern California, who scanned the brains of 69 smokers and ex-smokers to pinpoint the region involved. “This is very striking.”

Clearly brain damage isn’t a treatment option for people struggling to kick the habit.

But the finding, reported in Friday’s edition of the journal Science, does point scientists toward new ways to develop anti-smoking aids by targeting this little-known brain region called the insula. And it sparked excitement among addiction specialists who expect the insula to play a key role in other addictions, too.

“It’s a fantastic paper, it’s a fantastic finding,” said Dr. Nora Volkow, director of the National Institute on Drug Abuse and a longtime investigator of the brain’s addiction pathways.

“What this study shows unequivocally is the insula is a key structure in the brain for perceiving the urges to take the drug,” urges that are “the backbone of the addiction,” Volkow added.

Why? The insula appears to be where the brain turns physical reactions into feelings, such as feeling anxious when your heart speeds up. When those reactions are caused by a particular substance, the insula may act like sort of a headquarters for cravings.

Some 44 million Americans smoke, and the government says more than 400,000 a year die of smoking-related illnesses. Declines in smoking have slowed in recent years, making it unlikely that the nation will reach a public health goal of reducing the rate to 12 percent by the year 2010.

Nicotine is one of the most addictive substances known, and it’s common for smokers to suffer repeated relapses when they try to quit.

So imagine Bechara’s surprise at hearing a patient he code-named “Nathan” note nonchalantly that “my body forgot the urge to smoke” right after his stroke.

At the time, Bechara was at the University of Iowa studying the effects of certain types of brain damage after strokes or other injury. While Nathan was hospitalized, stroke specialists sent his information to that brain registry. He was 38, had smoked since 14, said he enjoyed it and had no intention to quit. But his last puff was the night before his stroke. His surprised wife said he never even asked for a smoke while in the hospital.

It’s not unusual for a health scare to prompt an attempt at quitting. “That’s the quitting that’s not as interesting,” Bechara said.