Researchers carefully implanted a tiny lens inside the mouse's brain. It's the lens for a microscope so small, the mouse can wear it like a hat.
The microscope can see neurons -- the cells that make up the brain -- firing with electrical impulses. It's the stuff neuroscientists have dreamed of and it could be the key to the mystery of memory.
"We think this is going to be useful both for understanding information processing in healthy brains and there also are applications in brain disease research," said Mark Schnitzer, an associate professor of biology and of applied physics.
Researchers found that when a mouse ran along a little track, every spot on the track lit up a specific neuron as the mouse scurried by.
"We can actually reconstruct where the animal is in space by looking simply at the brain activity movie," said Schnitzer.
But they found different sets of neurons light up on different days -- as if the brain is keeping its own backup, storing the same information in multiple places.
"One of the implications, I think, of the study is that the retention of spatial information may be surprisingly robust, at least in normal brains," Schnitzer said.
The idea of having a live window inside a working brain has so captivated the scientific community that in true Silicon Valley fashion, some of the researchers have gone and started a company, Inscopix, based around the technology.
"The data, when you look at it, it's just kind of beautiful, like a piece of art, and it really allows the researchers to kind of immediately see the data that they're collecting," said Laurie Burns, founding scientist at Inscopix.
The startup Inscopix plans to sell the miniature microscopes to brain researchers studying everything from aging to Alzheimer's disease.
"I really feel that using this technology, we can really help enable some truly fascinating research," said Burns.