The Triune Brain in Evolution: Role in Paleocerebral Functions

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Author: Anton Reiner
Date: Oct. 12, 1990
From: Science(Vol. 250, Issue 4978)
Publisher: American Association for the Advancement of Science
Document Type: Book review
Length: 2,576 words

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Paul MacLean was one of the trailblazers of neuroscience whose work in the 1940s and '50s provided many of the insights into the functions of the brain upon which today's neuroscientists build. MacLean in particular made contributions that drew attention to the role of brain areas such as the amygdala, septum, and cingulate cortex in emotion and motivation. He introduced the encompassing term limbic system to recognize the functional interrelatedness of these brain regions together with the hippocampus. Drawing on his own work and seemingly influenced by the prevailing view of brain evolution and the behavior of non-mammals (as reflected in the work of Elizabeth Crosby and C. J. Herrick), MacLean attempted to develop a comprehensive schema of brain function that would explain many major aspects of human behavior. This schema, which he set forth in the early '60s, was dubbed by him the triune brain because it involved the notion that the cerebral hemispheres of modern mammals, including humans, contain three distinct major regions - one inherited from reptiles, one inherited from early mammals, and one evolved in modern mammals. MacLean views each of these regions as controlling a specific set of behaviors. Hence he views the brain of modern mammals as exhibiting the sometimes unhappy cohabitation of an area with reptilian impulses (termed by him the reptilian or R-complex, which is often ignoble and always selfish), an area with early mammalian traits (termed the paleommalian complex, which is emotional but often noble and gentle), and an area devoted exclusively to rational and intellectual processes (termed the neomammalian complex).

Since he firsts introduced the triune-brain concept, MacLean has devoted himself to promoting and to carrying out studies to support it. These efforts have been rewarded by the reception the idea has been accorded outside the field of brain research. For example, it was a centerpiece to Carl Sagan's ruminations about the evolution of human intelligence in the best-selling book The Dragons of Eden, and it is frequently the only discussion of brain evolution in psychiatry and psychology textbooks.

The reasons for the popular appeal of the triune-brain idea are easy to see. For one thing, it pinpoints "big" behaviors that we are all interested in and finds causes for them. Further, it takes the "bad" behaviors, the things that we humans would rather not take blame for, and attributes most of them to a nonhuman, non-mammalian part of us, the purported reptilian beast in us. It takes the "good" behaviors, such as parental behavior and the related altruism, as well as the endeavors of art, science, and philosophy, and makes us feel that they are part of us as mammals and humans. These ideas tie in well with a longstanding human interest (at least in Western civilization) in attributing wayward human behavior to some nonhuman source - either to the beast within or to humankind's fall from God's grace due to the serpent-induced dereliction (those reptiles again) in the Garden of Eden. MacLean's Leaas are also appealing because they...

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Gale Document Number: GALE|A9012482