The origins of this approach are based upon work done in the early 1960's by Dr. Paul McLean and others who were attempting to explain the general function of various areas of the brain. Dr. McLean developed the 'Triune Brain' model for the structure of the brain he divided into three basic stages of development of the structure of the brain: the Reptilian Complex, the Paleomammalian Complex (Limbic) and the Neomammalian Complex (Neocortex).