Three layers of the brain are known for distinct functions (though all functioning areas constantly interact). Brain stem (fight or flight, instinct); Limbic system (emotion is processed); Four lobes at the top of the brain, generally where conscious thinking occurs. (Gurian, Michael, PhD, and Patricia Henley, with Terry Trueman. Boys and Girls Learn Differently! p 18. CA: Jossey-Bass, 2001.)

The fourth brain layer is defined as the prefrontal cortex. It can function, especially the left hemisphere portion, without being influenced unduly by the first two brain layers. (Pearce, Joseph Chilton. The Biology of Transcendence. p 36-38. VT: Park Street Press, 2002.)