As is usually the case in neuroscience, the revolution was triggered by improved technology, in this case, histotechnical advances heralding the emergence of new experimental methods to trace neuronal connections (see Basic Science Box 1).

As it turned out, while MacLean was developing his idea in the late 1960s and early 70s ( MacLean, 1970), the field of comparative neuroanatomy was undergoing a revolution of its own. Several reviewers of the concept questioned its compatibility with modern views of evolutionary neurobiology ( Durant, 1985 LeDoux, 1991 Butler and Hodos, 1996 Reiner, 1997). MacLean's notion of a hierarchical structure represented by the triune brain had popular appeal, and it reached beyond the research community as reflected by the books The Ghost in the Machine ( Koestler, 1967) and The Dragons of Eden ( Sagan, 1978), in which MacLean's notion of the triune brain was used in speculations on the human condition and destiny.Īlmost as soon as MacLean's triune brain was proposed, it came under fire. The evolutionary process was later followed in modern mammals by the development of the neomammalian brain (neocortex, related to problem solving and other cognitive functions).

MacLean suggested that a paleomammalian brain (represented by the limbic system, which according to MacLean is important in emotional behavior related to feeding, reproduction, and parental functions) was added in early mammals to the already existing reptilian brain (the basal ganglia, important for daily routines and ritual displays related to aggression, territoriality, and courtship). Zahm Ph.D., in Anatomy of Neuropsychiatry, 2008 2.1 THE TRIUNE BRAIN CONCEPT AND THE CONTROVERSY SURROUNDING IT

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