Core Memory Orbs are vitally important objects from the Disney/Pixar film Inside Out. These special kinds of Memory Orbs contain a very special memory (like an accomplishment or behavior trait), and it activates/creates an Island that serves as the basis of that person's personality and interest. Core memories are distinguishable from the other memories by their much brighter glow. They are stored in the center of the Headquarters. The core memories can be any from any emotion, but Riley's first five are yellow in color, meaning that Joy is the one who helped create these special memories. But one core memory was created by Sadness on the first day of school when Riley started crying about her move to San Francisco, which Joy immediately tried to get rid of, causing them to accidentally leave the Headquarters. During the events of the film, any memory Sadness touches becomes sad and can't be changed back, so Joy tries to prevent her from touching the core memories.
When Joy and Sadness get vacuumed out of Headquarters, the core memories were with them. Without the presence of the core memories, the islands that build up Riley's personality began to shut down and eventually break down and fall into the Memory Dump.
With the installation of the new controls, it seems that all of Riley's new core memories were formed by two emotions working together.