The Triune Brain

The Human Brain
        Paul MacLean, the former director of the Laboratory of the Brain and Behavior at the United StatesNational Institute of Mental Health, developed a model of the brain based on its evolutionary development. It is referred to as the "triune brain theory" because MacLean suggests that the human brain is actually three brains in one. Each of the layers or "brains" were established successively in response to evolutionary need. The three layers are the reptilian system, or R-complex, the limbic system, and the neocortex. Each layer is geared toward separate functions of the brain, but all three layers interact substantially.