Functional neuroscience Outline When a wild-type mouse—the variety that generally exists in nature—smells a cat, it feels fear and either freezes or runs away. Most people simply take it for granted that mice are afraid of cats, but elucidating the scientific mechanism that causes the brain to react with fear is no easy matter. Our team used genetic engineering to create a mutant mouse that could smell a natural predator but was unable to associate the odor with danger (see photo). This mouse taught us that the fear of a cat’s odor is an innate, genetically hard-wired response in mice. Lab head Reiko Kobayakawa, Ph.D. (Reiko@obi.or.jp) Kobayakawa et al., Nature vol.450, pp503-508 (2007)