"We really took the world's best memorizers — 23 memory champions out of the top 50 of the world. You wouldn't find anywhere in the world people more capable of memorizing stuff than them," says Dresler.
They did MRI scans of their brains, to take a look at the anatomy.
Then they scanned the brains of 23 regular people who were matched in age, gender and even IQ to the memory athletes. When Dresler and his colleagues compared the brain scans, they found no difference. At least, no big, obvious difference.
"That was actually really a bit surprising," he says.
But, when Dresler and his colleagues did functional MRI scans, which measure brain activity by looking at how much blood is going to specific portions of it, they did see a subtle difference in brain activity.
When memory athletes were asked to recite a long list of memorized words, some portions of brain were activating in unison — making 25 connections that seemed particularly significant among different parts of the brain. The scientists didn't see that sort of unified activity in the brains of the regular subjects.
In particular, parts of the brain associated with memory and with spatial learning seemed to be interacting a lot.
That makes sense, when you consider the tricks these athletes had learned to use when they memorize.
They weren't born with extraordinary memorization skills. They had all learned and practiced the same kind of training to develop their seemingly superhuman abilities.
Konrad, the memorizing whiz in Dresler's lab who is also a co-author of the study, started using the memory strategy as a hobby in high school, after watching memory championships on TV. He holds the world record for memorizing faces and names — 201 people in 15 minutes.
"I use my visual memory," says Konrad. If he's trying to remember a person called Miller, he says, "I would picture this person looking at a mill, maybe during a vacation in the Netherlands."
For more abstract memory challenges, like memorizing the exact order of hundreds of digits, he'll build memory palaces. It's a method that's been around since the Greeks and is covered extensively in the book Moonwalking With Einstein by journalist Joshua Foer.
It works by recalling a building or place that is very familiar and charting a mental path through that building.
"The very first one I ever did was in the home of my parents, where I still lived back then when I was still in high school," says Konrad.
Then, he memorizes an order of walking through that house.
"It would start in my room," he says. The first location would be my bed, and the second one would be the shelf above my bed; then it's my desk, the computer on it, the window, the mirror and so on."
To memorize abstract information, like a list of numbers, he would translate numbers into images and then distribute them along the mental path through his house.
For example, to memorize my phone number, which starts with "1202," Konrad transforms pairs of numbers into images, using something called the Major System.
The combination "1-2," for example, brings to mind (for him) a dinosaur, Konrad says. "So I would then picture a dinosaur standing on my bed," says Konrad. "It's a weird image. That's why it sticks."
"And then, 0-2 would be a sun. So, I would picture the sun illuminating the shelf over my bed," he says. And so on.
Memory Training Succeeds
In a second part of their study, Konrad and Dresler recruited 51 university students, and had one third of them do memory palace training for six weeks — once a week in person with Konrad, and half an hour a day at home on the computer. (If you want to give it whirl, here you go.)
Another group did a different kind of memory training, and the last group did nothing special.
Then, they were brought into the lab and were asked to memorize a list of words, like "night, car, yardstick," and so on.
The researchers used functional MRI machines to scan the brains of subjects as they rested, and again as they recited the list of words.
In the group that did memory palace training, Konrad, Dresler and their colleagues found that the volunteers' brain activity had changed to become more like that of the champions of memorization. This was the case when they were reciting numbers, but also when they were at rest.
"We showed that, indeed, the brain is somehow driven into the patterns you see in memory champions," says Dresler.
The subjects came back into the lab four months after training and got a new list of words to memorize. The ones who had done memory palace training did really well compared to the others, and their brains were still connecting in that new way.
"Not only during a task, but even in the complete absence of any memory-related activity, we see this effect — that memory champions differ from matched controls, and that after memory training your brain shows similar patterns," says Dresler.
"There are very few actual studies of people with remarkably superior memory who compete in these memory contests. This is by far the largest," says Roddy Roediger, a psychologist with Washington University in St Louis.
Roediger has studied people with exceptional memory for a long time. He says people knew that something different had to be going on inside the brains of these people.
"These people are the first to really uncover what that something may be," he says.
But Wait: The Fine Print
But this method of memory training is not the key to unlocking intelligence. In fact, it doesn't even seem to be the key to unlocking overall memory capability.
For example, Roediger knows a man capable of playing dozens of games of chess at the same time, while blindfolded.
"He had never heard of memory palaces," says Roediger.
There are also people who have memorized the Bible in its entirety and can recite portions of it on demand. And there are others who have a condition known as Highly Superior Autobiographical Memory, where they remember every day of their lives in sometimes excruciating detail.
"And yet, when you put them in memory tasks that memory competitors can do very easily, they can't do them any easier than you or I could," says Roediger. "So that's a real mystery."
The same limitations apply to people who have trained their memories.
If, for example, you ask the chess player or a Bible memorizer to remember a long list of words, says Roediger, "None of them can do that." Their techniques are specific to their tasks.
And, he says, intense memory training doesn't cure everyday forgetfulness.
"They forget the milk on the way home from work just like we do," says Roediger.