Tank's team designed an apparatus in which a mouse, its head firmly held in a metal helmet, walks on the surface of a styrofoam ball. The ball is kept aloft by a jet of air, so that it functions like a multidirectional treadmill. Around it are sensors taken from optical computer mice, which read the ball's movement as the mouse runs.
Those readings were the input for the researchers' virtual reality software -- a modified version of the open source Quake 2 videogame engine, tweaked to project an image on a screen surrounding the mouse. Tank called it "a mini-IMAX theater." Mice in the study ran through a virtual maze designed in the open source Quake game editor, but rather than earning points or power-ups, they were rewarded with sips of water from a head-side nozzle.
Into the hippocampus of each mouse the researchers inserted a glass capillary just one micron wide at its tip and filled with salt water. Known as a whole-cell patch recorder, it detects electrical currents as they pulse through individual cells.
"It is difficult to overstate the importance of understanding how the dynamics of electrical activity within single neurons is related to firing patterns among collections of neurons that accompany the performance of complex tasks," wrote Douglas Nitz, a University of California at San Diego cognitive scientist, in a commentary accompanying the findings.
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