It is a myth that people use only 10 percent of their brain, but it may be true that we use 20 percent to form memories. Working with mice and fluorescent probes, investigators monitored neurons in the lateral amygdalas, two almond-shaped regions on either side of the midbrain associated with learning and memory. In particular, they investigated the activity of the CREB protein, which plays a key role in memory formation in species ranging from sea slugs to humans, and they discovered that CREB activity occurs in one fifth of those midbrain neurons. Evidently neurons battle one another to make a particular memory. “It's like grading on a curve,” says study co-author Sheena Josselyn of the Hospital for Sick Children in Toronto. “The same number [20 percent] of students are going to get As”—or in the case of neurons, help make the memory. The findings appear in the April 20 Science.