Walk into any hotel room and you’ll immediately recognize the bed. You’ve probably never seen that particular bed before, but you know it’s a bed and you know what it’s for. That’s because our brains have this amazing ability to form abstract concepts, like learning what a bed is, and what a bed does. This week researchers at Boston University announced that they’ve identified individual cells in the brains of mice that appear to encode the concept of bed or in this case, nest. The researchers had implanted electrodes in the brains of mice to study how neurons act together to form memories. In the course of their work they stumbled across a few cells that were only active when the mice returned to their cages and curled up in their nests. These neurons, it turns out, responded vigorously to anything that even resembled a nest whether it was round, square or triangular, or made of cotton, plastic or wood. But when the researchers covered the nest with a glass dish, so the mice could still see it but they couldn’t climb in, the cells fell silent. Now those are some pretty smart cells. After all, a bed under glass is not really a bed - it’s a museum exhibit.