This is the 2007 version. Click here for the 2017 chapter 09 table of contents.

Limbic Origins of Emotion

Neurologist Paul D. MacLean is famous for inventing the term limbic system. MacLean's theory of the triune brain (three-part brain) identified three areas of differing phylogenetic or evolutionary age. The oldest part of the brain is the so-called "reptilian brain" which is present in virtually all animals. It controls behavior dominated by olfaction—the sense of smell. The olfactory lobe of the brain, which directly overlies the sinus cavities in humans, is primitive, meaning it is found in virtually all animals. Called the rhinencephalon, literally the "smell brain," this area controls many animal activities that typically involve the sense of smell: food gathering, courtship, mating, and warning of predators.

What is MacLean's "triune brain" concept?

The second part of the brain, which MacLean claimed was unique to mammals, is the limbic system. MacLean (1949) originally called it the visceral brain because of its close ties to the autonomic nervous system. MacLean coined the term "limbic system" in 1952 and it is now widely used to describe the deep forebrain structures, below the cerebral cortex but above the brain stem.

The third brain area is the neocortex (literally "new cortex"), which corresponds to the cerebral hemispheres in humans. As we saw in Chapter 2, humans have far more neocortex than any other species. MacLean suggested that the neocortex produced the intellect, which overlies and controls the impulses of the limbic system.

Which part of the limbic system is most involved in regulating emotion?

MacLean's triune brain concept is an oversimplification, and in some ways it is simply wrong (animals other than mammals have rudiments of a limbic system, for example) but the name limbic system stuck. The limbic system is a group of related midbrain structures. These structures are anatomically distinct but they work as a team, and much of their work involves emotions. The limbic system is the location of the so-called pleasure centers.

The part of the limbic system most crucial for negative emotional expression is the amygdala. Anderson and Phelps (2000) concluded, a "growing body of evidence" points to the amygdala as the brain structure most responsible for controlling emotion. The oft-cited superiority of the right hemisphere for emotional processing is due mostly to the activity of the amygdalar region on that side of the brain.


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