The mice with the modified astrocytes seemed perfectly healthy. But after several cognitive tests, the researchers found that they failed in one major area: novel object recognition. As expected, healthy mouse spent more time with a new item placed in its environment than it did with familiar items. In contrast, the group's new mutant mouse treated all objects the same.
"That turned out to be a spectacular result in the sense that novel object recognition memory was not just impaired, it was gone—as if we were deleting this one form of memory, leaving others intact," Sejnowski says.
The results were surprising, in part because astrocytes operate on a seconds- or longer timescale whereas neurons signal far faster, on the millisecond scale. Because of that slower speed, no one suspected astrocytes were involved in the high-speed brain activity needed to make quick decisions.
"What I thought quite unique was the idea that astrocytes, traditionally considered only guardians and supporters of neurons and other cells, are also involved in the processing of information and in other cognitive behavior," says Verma, a professor in the Laboratory of Genetics and American Cancer Society Professor.
It's not that astrocytes are quick—they're still slower than neurons. But the new evidence suggests that astrocytes are actively supplying the right environment for gamma waves to occur, which in turn makes the brain more likely to learn and change the strength of its neuronal connections.
Sejnowski says that the behavioral result is just the tip of the iceberg. "The recognition system is hugely important," he says, adding that it includes recognizing other people, places, facts and things that happened in the past. With this new discovery, scientists can begin to better understand the role of gamma waves in recognition memory, he adds.