A lot of what we think of as thinking happens at the brain's outer limits. A blanket of cells, marked with deep creases, swaddles the core of the brain in every animal with a spine. This blanket integrates all kinds of information, makes decisions, interprets emotions, solves problems and creates complex behavior. It is called the cerebral cortex, and neurons in it—humans have about 16 billion—act a bit like tiny information processors to form thoughts.