Thirsty animals seek water. In mice, this vital impulse is motivated not by the brain signalling an attraction to water, as some studies have suggested, but by the feeling of thirst being perceived as unpleasant.
Karl Deisseroth, Liqun Luo and their colleagues at Stanford University in California worked this out by dissecting the neural circuitry involved. They identified in mouse brains a cluster of neurons that were activated after two days of water deprivation.
When the scientists inhibited these neurons, the water-deprived mice drank less. When they activated the neurons, even mice that had ample access to water drank more. Non-deprived mice even worked hard for water by repeatedly pressing a lever.
When those mice were taught how to turn off the activated neurons by pressing a different lever, they did so vigorously, indicating that they experienced the artificial feeling of thirst as unpleasant.