Thursday, January 10, 2008

Obit: Dr. Paul MacLean

From The New York Times:

Paul MacLean, 94, Neuroscientist Who Devised ‘Triune Brain’ Theory, Dies
By JEREMY PEARCE
Published: January 10, 2008

Dr. Paul D. MacLean, a neuroscientist and psychiatrist who developed the intriguing theory of the “triune brain” to explain its evolution and to try to reconcile rational human behavior with its more primal and violent side, died on Dec. 26 in Potomac, Md. He was 94.

Dr. MacLean’s death was confirmed by his family.

In the late 1940s, while he was a young researcher at Yale, Dr. MacLean became interested in the brain’s control of emotion and behavior. After initial studies of brain activity in epileptic patients, he turned to cats, monkeys and other models, using electrodes to stimulate different parts of the brain in conscious animals. He then recorded the animals’ responses and, in the 1950s, began to trace individual behaviors like aggression and sexual arousal to their physiological sources.

Dr. MacLean (pronounced mac-LANE) termed the brain’s center of emotions the limbic system, and described an area that includes structures called the hippocampus and amygdala. Developing observations made by Dr. James W. Papez of Cornell, he proposed that the limbic system had evolved in early mammals to control fight-or-flight responses and react to both emotionally pleasurable and painful sensations. The concept is now broadly accepted in neuroscience.

Dr. MacLean said that the idea of the limbic system leads to a recognition that its presence “represents the history of the evolution of mammals and their distinctive family way of life.”

In the 1960s, Dr. MacLean enlarged his theory to address the human brain’s overall structure and divided its evolution into three parts, an idea that he termed the triune brain. In addition to identifying the limbic system, he pointed to a more primitive brain called the R-complex, related to reptiles, which controls basic functions like muscle movement and breathing. The third part, the neocortex, controls speech and reasoning and is the most recent evolutionary arrival.

In Dr. MacLean’s theory, all three systems remain in place and in frequent competition; indeed, their conflicts help explain extremes in human behavior.

In the 1970s and ’80s, aspects of Dr. MacLean’s model were popularized by the astronomer Carl Sagan and the novelist Arthur Koestler.

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