By analyzing results of the memory test, the researchers picked out a group of volunteers who stayed sharp, even after two all-nighters. The next step was to examine these people's MRI scans to figure out which brain networks were responsible for the memory boost.
"We could see what brain networks were more activated in those people who were more resilient to the sleep deprivation," says Lisanby.
But she says, "Just seeing that that network is more active in the resilient person doesn't prove that that's how they were doing it, that that's how they were resisting the sleep deprivation." That's why they used TMS, "guided by those brain imaging results, to test whether that network was responsible for those people's ability to be resilient to sleep deprivation," Lisanby explains.
Simply put, the researchers saw what worked for the resilient volunteers, and they used TMS to replicate that beneficial brain state in the volunteers most affected by losing sleep.
While the MRI scans provide the maps of each volunteer's brain, they can't steer the magnetic fields. So to make sure the magnets hit the right spot, the researchers hook up the TMS device to an infrared camera that tracks the research subject's location in the lab room. The camera and the MRI data both feed to a computer, and the computer tells the researcher where to aim the magnet. Lisanby's co-author, Bruce Luber, says TMS is accurate enough to send the magnetic signal to within millimeters of the targeted brain region.
As the researchers wrote in the journal Cerebral Cortex, TMS recipients were speedier in memory tests following the treatment.
Lisanby says, "That's the part that we find really exciting — that not only has it taught something new about how the brain works, how the brain responds when you're sleep-deprived, but it also might shed light on a new direction for using image-guided TMS as a way of improving memory in the future."
The research, which was funded by the Department of Defense, may one day be able to help sleep-deprived soldiers, says Lisanby. "Our men and women in uniform might be in missions where they need to be sleep-deprived for certain periods of time. So that's another situation where it's important to learn about how sleep deprivation affects our function," she says.
Could TMS also be used to improve performance if you aren't short on sleep? In their 2007 paper published in the journal Brain Research, the researchers showed that they could improve working memory slightly in well-rested people as well. But for TMS to make a difference for these normal volunteers, it needed to target different brain regions than those targeted in the sleep-deprived group.
"The region of the brain that helped the people who weren't sleep-deprived was actually different from the brain region that helped the people who were sleep-deprived," Lisanby explains.
But that doesn't mean you'll be boosting your brain with TMS tomorrow. "We're at the very early stages of this research," she says. "It's a far leap before we would get to the point where something like this would be of use outside of the laboratory. But it's certainly something that we hope that research will begin to look towards."
This research was published in Cerebral Cortex, January 17, 2008, and was funded by a Defense Advanced Research Projects Agency (DARPA) Award.