Mind reading? Maybe. Researchers have successfully identified where people are "standing" in a virtual-reality environment by analyzing which neurons they're using. The findings may help scientists understand how memory goes awry in neurological diseases such as Alzheimer's.
Researchers have already made progress in reading rat minds. By recording the firing patterns of neurons called, appropriately enough, place cells, scientists have been able to pinpoint a rat's location in a laboratory maze. But such studies can only record activity in a tiny fraction of the millions of neurons thought to play a role in spatial memory; some researchers felt they might learn more by looking at all of those millions at once.
So Demis Hassabis and Eleanor Maguire, neuroscientists at University College London, and their colleagues turned to fMRI (functional magnetic resonance imaging), which measures brain activity through changes in blood flow. They asked four male volunteers to navigate through two rooms in a virtual-reality program (see picture) and to stop repeatedly at eight different marked locations, while the fMRI scanned a region of their brain known as the hippocampus. (In 2000, some of the same researchers showed that the rear portion of the hippocampus in London cabbies--masters of navigation--was larger and differently shaped than in other adult men, suggesting that this area was important for spatial memories).
Bringing the virtual-reality environment to the subjects was tricky, because according to Hassabis, "you can't have any metal [like virtual-reality goggles] inside the scanner--it would get ripped apart." Instead, the team projected the environment onto two mirrors positioned just above the subjects' eyes. A special joystick-like control pad allowed the volunteers to move around the environment while lying motionless in the scanner.
Publishing online 12 March in Current Biology, the team reports that after analyzing scans from several stops at each location, a customized computer algorithm was able to consistently identify in which of the eight locations a subject was "standing." But Hassabis notes that, although the algorithm could differentiate between the locations based on activity patterns, it's not clear exactly what patterns the spatial memory is storing. He says that if researchers can determine what spatial memory actually encodes, they'll have come a step closer to understanding how memory works in healthy people, and "why the system breaks down in disease[s] ... such as Alzheimer's."
The experiment is "an impressive demonstration of our ability to decode thoughts in the brain," says Howard Eichenbaum, a hippocampal neuroscientist at Boston University. "It suggests there must be a hidden ... map" representing our position in space across the hippocampus, adds Edvard Moser, a neuroscientist at the Norwegian University of Science and Technology in Trondheim.
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