A decade ago, several independent brain studies found that adults continue to grow new neurons, overturning a long-held belief that the number of cells in a grown-up's brain can only move in one direction: down. Many scientists suggested that this continued "neurogenesis"—which mainly happens in a small region called the hippocampus—might explain how people continue to learn and adapt in new environments long after birth. But a new mouse study suggests that learning and memory may not depend on neurogenesis. The research raises questions about both the purpose of those mysterious new brain cells and the neurobiology behind adult learning.
For most lab mice, home is a pretty austere place. Five critters share a plastic cage, only slightly bigger than a loaf of bread, lined with wood chips and holding nothing but food and water. Previous experiments had shown that putting mice in more stimulating environments—much larger cages with cubbyholes, ...
