By outfitting a PET scanner with a virtual reality world, researchers have mapped brain regions as a person navigates through an environment. The research, described in today's Science, reveals a tight link between how humans and other mammals keep track of direction and location. What's more, the technique could be used to assess the disorientation that can accompany brain damage as in Alzheimer's disease and perhaps test drugs that might help these patients.
Experiments with rodents have shown that a portion of the brain called the hippocampus, long associated with memory, has a key role in navigation. Indeed, the hippocampus in rats even seems to contain a so-called cognitive map, since particular neurons fire in response to certain locations in an environment. Researchers have found that in humans, the hippocampus of the brain's right hemisphere is particularly busy during navigation. But these studies have been passive--people watching videos or London taxicab drivers recalling their routes. A team of neuroscientists led by Eleanor Maguire at University College London wanted to monitor brain activity while people were actively engaged in navigation.
Since it's hard to trot around while being PET-scanned, the researchers converted a video game called Duke Nuke'm into a town that people could see on a screen and walk through by pressing a keypad. Ten male volunteers were given an hour to explore the virtual streets and shops, thereby creating a mental map. Then researchers used a PET scan to measure brain activity while the subjects followed a path labeled with arrows--a task requiring no navigation. Later, the people had to find their way without arrows from one point to another, say from the movie theater to the sushi bar.
It turns out that the more accurate a subject's route, the more active the right hippocampus, which dovetails with its role in supporting spatial maps. Navigating quickly was strongly associated with activity in another brain region, the right caudate nucleus, which fits with its proposed role in motor learning.
"It's a lovely piece of work," says Eric Kandel, a psychiatrist at Columbia University who studies the hippocampus. The findings show that the same brain regions are involved in how both humans and mice or rats navigate. And that suggests these animals could be used to test for drugs that might help restore hippocampal function in those with dementing disorders.