Like many freshwater turtles, the slider Trachemys scripta can spend the whole winter resting at the bottom of a cold lake with no oxygen. Are they totally comatose, or do they keep a bit of a light on in their brains? To find out, researchers inserted electrodes into anesthetized turtles' heads. The reptiles’ neurons responded to light and vibration—even when the turtles were deprived of oxygen , the group reports online today in Biology Letters. The team also placed nonanesthetized turtles in cold, oxygen-free water in a dark lab for 2 weeks, to make them think it was winter. When the researchers turned on the lights, the turtles started moving around in their tanks. Warming the water had the same effect. (Oxygen and vibration didn't.) The team concludes that the turtles aren't actually comatose in winter; they're waiting for signs of spring in a state of "slow vigilance."