WASHINGTON (CNN) -- It's a classic pattern. You remember the name of your kindergarten teacher, but you can't remember the plot of the movie you saw last night. Researchers believe they can partly explain why. They have identified the areas of the brain that become more active when we remember.

In a unique pair of studies conducted in 1998, scientists at Harvard and Stanford universities used sophisticated imaging techniques to watch people's neural activity and, for the first time, show which parts of the brain determine whether a specific experience will be remembered or forgotten.

The findings "mark a significant step forward," said memory expert Michael D. Rugg of Britain's University of St. Andrews, who critiqued the studies in the journal Science.

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That discovery means advertisers might one day figure out how to make commercials better stick inside the consumer brain. "Advertisers, of course, are very interested in what's going to be remembered, what's going to be forgotten," said Stanford neuroscientist James Brewer, who led the memory study. "They want their stuff to be tied into your brain. So, if someone wanted to see what type of material might activate this region more than another region, that could be something applied to education or advertising."

Because Alzheimer's disease ravages one of these memory-making regions, the scientists studied whether their findings also could help detect the devastating brain disease in its earliest stages.

Alzheimer's patients often have vivid memories of past experiences, but new memories are easily forgotten. To date, the only way to diagnose Alzheimer's positively is by autopsy, but the scientists feel their studies are key to starting timely treatment.

"We're really excited about the prospect of this being used for Alzheimer's disease," said Brewer. "If we were able to detect Alzheimer's really early, the prospect for treatment is much, much better."

Scientists have long suspected that how well people remember depends on differences in how their experiences are "encoded" into the brain at the time they occur. Studies of people with brain damage have suggested various brain regions were involved, but it wasn't clear if damage to those regions meant people couldn't make new memories, retrieve old ones or store memories over time.

New, high-powered "magnetic resonance imaging," or MRI, machines work fast enough that scientists can measure split-second neural activity as a person's brain processes an experience.

At Harvard, neuroscientist Anthony Wagner put healthy volunteers into these "functional MRI" machines and rapidly flashed one word every two seconds onto a screen inside. At first, the volunteers merely noted whether words were in upper- or lower-case letters. With additional words, they were told to decide if each was concrete, like "chair" or "book," or abstract, like "love" or "democracy."

That's because psychologists already knew that analyzing the meaning of a word helps people remember it. In Stanford's study, Brewer showed volunteers color photographs of indoor and outdoor scenes rather than words.

Neither set of volunteers had been told this was a memory test. But after the MRI scans, they were asked which words or pictures they remembered well, remembered vaguely or didn't remember. The scientists compared those memories to the brain scans.

The longer that two brain regions -- the prefrontal lobes and the parahippocampal cortex -- both lit up on the MRI scans, the better people remembered the items. Words or pictures that caused weak activity in the two regions were forgotten.

What makes your brain more likely to react to one item over another? "That's the million-dollar question," Wagner said.

The studies provided some hints. Wagner's volunteers showed more neural activity and better memory during the "concrete-abstract" word test than for other words, providing biological evidence that more complex cognition increases the chances of memory.

And personal experiences probably play a role. Perhaps Brewer flashes a photo of Zion National Park: Someone who just visited there may react more than someone who says, 'Oh, a desert scene.' Most people think of memory problems as "failing to retrieve an event," Brewer explained.

Instead, think of "what went on when you put those car keys down that distracted your attention from where you're putting them," he said. "But you're thinking of that stupid piece of trivia, you're attending to it" -- so the trivia of, say, a TV show becomes a memory.

CNN Correspondent Rusty Dornin and The Associated Press contributed to this report.