 Ulfaction is a sense that has been shaped by evolution to detect and respond to chemicals in the environment. A recent study found that the brain's representation of odors follows a pattern based on the chemical structures of the molecules involved. This pattern, called the principal odor map, POM, is similar to the way the visual system processes light and shapes. The POM may help explain why certain odors often occur together and why some odors are easier to detect than others. This article was authored by Wesley W. Chen, Jennifer N. Wei, Benjamin Sanchez Lengeling, and others.