An anonymous reader writes "In this week's issue of Nature, scientists from Princeton University trained mice to navigate around a virtual environment using a setup that resembles a combination of a giant trackball and a mini-iMax theater displaying a virtual world rendered using a modified version of the Quake 2 open source game engine. (Here's the academic paper, subscription required.) They hold the mouse's head still atop a giant trackball, which the mouse turns by running. The scientists use the rotations to move the mouse around in the virtual environment, and when he reaches certain places, he gets a reward. Because they are able to hold the head still, they can stick microscopic glass electrodes into individual neurons in the hippocampus of this mouse as it 'navigates.' They find the neural activity that resembles activity during real life navigation, and learned new things about the inputs and computations that are going on inside these neurons, which weren't known before. No word as of yet whether the scientists plan on giving the mice control of the gun. Wonder whether John Carmack ever envisioned this when he opened up the Quake code?"