Image: JEREMY CAPLAN
It's impossible to pinpoint where our ability to navigate lies. The brain has no central GPS unit. But scientists are homing in on just how we figure out which way to turn in familiar environments. Recent studies have illuminated our use of both visual cues and language. And a new paper in the June 24 issue of Nature reports that spatial reasoning in people actually produces specific patterns of electrical activity called theta oscillations.
Earlier work had linked slow, rhythmic theta oscillations and way-finding in rats, but it was hard to make the same connection in humans. Noninvasive methods for observing the brain in action--such as magnetic resonance imaging (MRI) and positron-emission tomography (PET)--don't pick up on brain waves. To see them, Michael Kahana, Robert Sekuler, Jeremy B. Caplan and Matthew Kirschen of Brandeis University, along with neurosurgeon Joseph R. Madsen of Boston's Children's Hospital, enlisted the help of three teenagers.
All three teens had severe epilepsy, a condition characterized by electrical storms of sorts in the brain. And for all three, medication had failed to control the seizures that result. Consequently, they were due for delicate surgeries in which doctors excise the regions in their brains where the storms originate. To make certain they don't damage healthy and essential tissue, doctors first monitor such patients using electrodes placed directly on the brain's surface. It was these electrodes that allowed Kahana and his crew to record theta waves.
Image: JEREMY CAPLAN
To prompt spatial reasoning in their subjects, the researchers had them play a video game--essentially a collection of long and short 3-D virtual mazes designed by a 15-year-old student for the study. Four times the teens went through each maze with arrows directing them to the end. Then they were asked to navigate each maze unaided until they could traverse its length without errors at least three times in a row.
In both cases, the task generated strong episodes of theta-wave activity in all three subjects and in many different areas of the brain--including the temporal cortex, a region involved in memory and often epilepsy. Moreover, longer mazes brought on more frequent periods of theta oscillations. Of interest, theta episodes were also more common when the teens were trying to recall the maze, not learn it in the first place. Although there could be no control group--and so the scientists cannot guarantee that these patterns arise in non-epileptic brains as well--there is every reason to be confident that they do: in one subject, the epileptic tissue and that creating strong theta waves were entirely separate.
Not only does the study confirm that rats and people have similar brain activity while wending their way around mazes, it also opens up new avenues to explore for treating epilepsy. "By playing video games today, these heroic teenagers are helping the kids of the future have happier, healthier, seizure-free lives," Sekuler notes. "With more work, we may be able to understand why the brain's rhythmic activity sometimes spins out of control. Our long-range goal is developing a cure for epilepsy."