Adult rodents form more new neurons than usual when placed in spacious habitats with toys and running wheels, so researchers had supposed that neuron formation, called neurogenesis, also causes the decreased anxiety as well as the enhanced learning and memory brought on by richer environments. Looking to test the connection further, Columbia University researchers precisely irradiated and disabled the hippocampal region where mice form new neurons. Surprisingly, when placed in enriched surroundings, the irradiated mice performed just as well as intact rodents in spatial learning tests and were equally less anxious. The result suggests neurogenesis is not responsible for the effects of enrichment, at least in mice, the investigators note in the April 30 online Nature Neuroscience. The study also raises tantalizing questions about the role of neurogenesis in humans, as some research has suggested that the process is important in the treatment of depression.