The life and career of Paul MacLean. a journey toward neurobiological and social harmony.

Working as a physician, Paul MacLean's interests moved in the direction of the brain when he realized that most of his patients suffered from symptoms (e.g. anxiety, sleeping problems) that could not be traced to a known physiological cause. His curiosity about the neurological origins of these psychological symptoms led him to the laboratories of Stanley Cobb and James Papez, both of whom were influential in guiding MacLean's interests toward the temporal lobe. His neurobiological interest was not contained, however, to the temporal lobe. As his own family grew to include a wife and five children, his scholarly pursuits extended to social and familial relations and their accompanying underlying neuroanatomical circuits (i.e. the thalamocingulate system). Viewing the brain and behavior from an evolutionary perspective, MacLean introduced the concept of the "triune brain" to describe the evolutionarily distinct components of the mammalian brain and reintroduced Broca's term "limbic" to describe a neuroanatomical system involved in emotional functions. MacLean wrote that the development of social behaviors, such as mother-infant audiovocal communication and the separation cry of the offspring, served as the driving force in the evolution of the neocortex. MacLean's neuroevolutionary perspective and appreciation of the complexity and evolutionary significance of social systems offer valuable insights into the contemporary fields of behavioral neuroscience and biological psychiatry.