What is a brain trust in Pixar?

Could you please elaborate on the concept of a "brain trust" within Pixar Animation Studios? I'm particularly interested in understanding the role it plays in fostering creativity and innovation in the development of their animated films. Additionally, I'm curious to know if this brain trust operates as a formalized group or if it functions more organically as a collection of individuals who collaborate on projects. How does this approach contribute to the success and distinctive style of Pixar's output?