Lucky Triune Brain

Chronicles of Paul D. MacLean’s Neuro-Catchword

in Nuncius
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The triune brain idea has been rated as the most influential in post-war neuroscience. The first part of this article seeks to retrace its genesis and development through the vicissitudes of the research conducted by Paul D. MacLean (1913–2007). Ten years have passed since his death: despite the loss of scientific credit, the apparent simplicity of his tripartite theory continues to exert a certain popular appeal. In the second part of the article an attempt is made to figure out how the transfer from the laboratory to public fruition could happen. The man initially responsible for the operation was MacLean himself, then aided by a few followers who had the means to spread his message of salvation. Against the background of the Cold War, and while Western culture started to realize the threat posed by overpopulation, pollution, and the exhaustion of critical resources, they deluded themselves that “knowing the brain” might suggest new and more effective approaches to the troubles of the oncoming end of the century. Consulting MacLean’s papers in the archives at the National Library of Medicine (Bethesda, MD) has been essential to this historical reconstruction.

Lucky Triune Brain

Chronicles of Paul D. MacLean’s Neuro-Catchword

in Nuncius




John Durant“Knowledge and Values in Neurobiology: The Case of the Triune Brain,” in So Human a Brain. Knowledge and Values in the Neurosciencesedited by Anne Harrington (Boston Basel Berlin: Birkhäuser 1990) pp. 268–269.


Jeremy Pearce“Paul MacLean, 94, Theorized a ‘Triune Brain,’ ” The New York TimesJanuary 10 2008 A28; Peter Farley “A Theory Abandoned but Still Compelling” Yale Medicine 2008 43:16–17.


Antonio R. Damasio G.W. Van Hoesen“Emotional Disturbances Associated with Focal Lesions of the Limbic Frontal Lobe,” in Neuropsychology of Human Emotionedited by Kenneth M. Heilman Paul Satz (New York London: The Guilford Press 1983) pp. 85–110: 87. A similar remark would also be made by Joseph LeDoux who acknowleged that MacLean’s synthesis was an “amazing achievement” – broad in its scope wide-ranging in its implications and long-lived – but unfortunately not acceptable because of the scarce evidence for the existence of the limbic system or its involvement in emotion. As survival functions emotions are manifold and each may well involve different brain systems; see Joseph LeDoux “Emotion and the Limbic System Concept” Concepts in Neuroscience 1991 2:169–199; Id. The Emotional Brain. The Mysterious Underpinnings of Emotional Life (London: Weidenfeld & Nicolson 1998) pp. 92–103.


Anton Reiner“An Explanation of Behavior,” Science1990 250:303–305; C.B.G. Campbell review of The Triune Brain in Evolution: Role in Paleocerebral Functions by Paul MacLean American Scientist80/5:497–498. For a reply to critics see Gerald A. Cory Jr. “Reappraising MacLean’s Triune Brain Concept” in Gerald A. Cory Russell Gardner The Evolutionary Neuroethology of Paul MacLean. Convergences and Frontiers (Westport CT – London: Praeger 2002) pp. 9–27 which contains twenty contributions by various authors 400 pages of positive evaluation. According to the book’s coeditors MacLean had been trying to address the larger questions of human behavior while other researchers were much more interested in the fine-grained technical questions: whence the roots of the tension (pp. 21–23).


See for instance Walter J. FreemanSocieties of Brains. A Study in the Neuroscience of Love and Hate (New York, London: Psychology Press1995) pp. 168–169; Ann B. Butler William Hodos Comparative Vertebrate Neuroanatomy. Evolution and Adaptation (New York: Wiley-Liss 1995) p. 86; Arnold H. Modell “Are Mental Functions Hierarchical?” The Annual of Psychoanalysis 2000 28:127–135; and Paul Patton “Many Minds: Intelligence in the Animal Kingdom” Scientific American 2008 19:72–79. Patton asserts that according to recent findings in comparative neuroanatomy complex brains evolved independently in multiple phyla and times among various groups of vertebrates. Therefore no sequential line would be plausible.


Ben Thomas“Revenge of the Lizard Brain,” Scientific AmericanGuest Blog September 7 2012.


Kelly G. Lambert Robert Gerlai“The Neurobiological Relevance of Social Behavior: Paul MacLean’s Legacy,” Physiology and Behavior2003 79:341–342; Detlef W. Ploog “The Place of the Triune Brain in Psychiatry” Physiology and Behavior 2003 79:487–493 p. 492.


Ibid. p. 251.


Ibid. p. 255.


James W. Papez“A Proposed Mechanism of Emotion,” Archives of Neurology and Psychiatry1937 38:725–743 p. 743.


MacLean to Papez November 2 1948Paul D. MacLean Papers 1936; 1944–1993. Located in: Archives and Modern Manuscripts Collection History of Medicine Division National Library of Medicine Bethesda MD; MS C 534. (henceforth MLP) Box 2 – Correspondence folder 32.


MacLean to Papez November 15 1948MLP Box 2 – Correspondence folder 32. The envelope contained also a review of Wiener’s Cybernetics that had just come out with MacLean’s comment: “This book will be of tremendous interest to you because it introduces the concept of scanning and negative feed-back mechanisms which are implicit in your paper Structures and mechanisms underlying the cerebral functions. It is Professor Wiener’s thesis that the brain and the computing machine as well as other servomechanisms have much in common. I shall bring along a copy of Wiener’s books which I’ll present to you.”


MacLean to Papez November 30 1948MLP Box 2 – Correspondence folder 32.


MacLean to Papez February 17 1949MLP Box 2 – Correspondence folder 32.


Papez to MacLean February 25 1949. “You will be remembered” MacLean emphasized in his reply “as the man who localized the id!” (MacLean to Papez March 8 1949 MLP Box 2 – Correspondence folder 32).


Paul D. MacLean“Psychosomatic Disease and the Visceral Brain. Recent Developments Bearing on the Papez Theory of Emotion,” Psychosomatic Medicine1949 11:338–353 p. 351.


Ibid. p. 338.


See Heinrich Klüwer Paul C. Bucy“Preliminary Analysis of Functions of the Temporal Lobes in Monkeys,” Archives of Neurology and Psychiatry1939 42:979–1000.


MacLean“Psychosomatic Disease” (cit. note 20), p. 348 (italics in text). For a history of the terms, see Régis Olbry, Duane E. Haines, “Rhinencephalon: a Brain for the Nose?,” Journal of the History of the Neurosciences1997 6:217–218; Id. “From Dante Alighieri’s Circle to Paul Donald MacLean’s Limbic System” Journal of the History of the Neurosciences 2005 14:368–370.


See Paul Broca“Anatomie comparée des circonvolutions cérébrales. Le grand lobe limbique et la scissure limbique dans la série des mammifères,” Revue d’ Anthropologie1878 7:385–498.


Paul D. MacLean“Some Psychiatric Implications of Physiological Studies on Frontotemporal Portion of Limbic System (Visceral Brain),” Electroencephalography and Clinical Neurophysiology1952 4:407–428. In a letter to Stanley Cobb MacLean explained how he had come to introduce the term which would avoid any preconception as regards function (January 18 1956 MLP Box 1 – Answered Letters folder 18). See also Id. “The Limbic System and its Hippocampal Formation. Studies in Animals and their Possible Applications to Man” Journal of Neurosurgery 1954 11:29–44.


MacLean to George L. Engel November 10 1953MLP Box 9 – Series IV: Professional Activities folder 23 (American Psychosomatic Meeting).


Papez to MacLean May 15 1956MLP Box 2 – Correspondence folder 32.


Breitenberg to MacLean August 9 1956MLP Box 3 – General Correspondence folder 1. MacLean to Moruzzi April 4 1957; Moruzzi to MacLean April 8 1957 and May 8 1957 Box 3 – General Correspondence folder 2. Wolstenholme to MacLean November 28 1956; MacLean to Wolstenholme January 10 1957; Wolstenholme to MacLean March 20 1957 MLP Box 9 – Series IV: Professional Activities folder 42.


MacLean to Lorenz October 20 1959MLP Box 8 – Comparative Behavior Research Center folder 1. MacLean’s itinerary in Europe included a visit to Nikolaas Tinbergen at the Department of Zoology Oxford.


MacLean to Livingston November 14 1958MLP Box 6 – Series III: National Institute of Health Brain and Behavior Reserve folder 40.


Livingston to MacLean March 12 1959Box 6 – Series III: National Institute of Health Brain and Behavior Reserve folder 41.


Carmichael to MacLean May 12 1964MLP Box 1 – Answered Letters folder 13; Paul D. MacLean “Man and his Animal Brain” Modern Medicine 1964 32:95–106; Stanley Finger Origins of Neuroscience. A History of Explorations into Brain Function (Oxford: Oxford University Press 1994) p. 290. Others have noticed that a hierarchical tripartite organization is inherent to Freud’s structure of the mental apparatus or that similar models based on the ‘magic’ number three occur not infrequently during the 20th century; see Luciano Gallino “Il contributo di Paul D. MacLean a una scienza unitaria del comportamento umano” in Paul D. MacLean Evoluzione del cervello e comportamento umano (Torino: Einaudi 1984) pp. VIILV; Gerald Wiest “Neural and Mental Hierarchies” Frontiers in Psychology 2012 3:1–8; Lazaros C. Triarhou “Tripartite Concepts of Mind and Brain” in Cognitive Psychology Research Developments edited by Stella P. Weingarten Helena O. Penat (New York: Nova Science 2009) pp. 183–208.


Koestler to MacLean October 13 1965MLP Box 3 – General Correspondence folder 37. See David Cesarani Arthur Koestler: The Homeless Mind (New York: Free Press 1998). According to the testimony of Koestler’s third wife “MacLean’s work came at the right moment when a number of ideas on this theme were in chrysalis form”: Cynthia Koestler “Twenty-Five Writing Years” in Astride the Two Cultures. Arthur Koestler at 70 edited by Harold Harris (New York: Random House 1975) pp. 136–148: 143.


Koestler to MacLean November 22 1966MLP Box 3 – General Correspondence folder 37.


Koestler to MacLean July 7 1968MLP Box 3 – General Correspondence folder 37. The European Forum in Alpbach (Tyrol) was founded in 1945 by the federalist Otto Molden as an interdisciplinary venue for a peacefully united Europe. Since 1959 Koestler had owned a house for summer vacations there and helped organize several symposia. His work in view of the 1968 conference is documented by the correspondence with MacLean whose paper The paranoid streak in man was afterwards included in Beyond Reductionism. New Perspectives in the Life Sciences. The Alpbach Symposium 1968 edited by Arthur Koestler John R. Smythies (London: Hutchinson 1969) pp. 258–278. The Wenner-Gren Foundation Symposium had been organized by Gregory Bateson and held in Burg Wartenstein Castle (July 16–25 1968): see Mary Catherine Bateson Our Own Metaphor. A Personal Account of a Conference on the Effects of Conscious Purpose on Human Adaptation (New York: Alfred A. Knopf 1972).


MacLean to Koestler February 7 1969MLP Box 3 – General Correspondence folder 37.


MacLean to Koestler November 8 1971MLP Box 3 – General Correspondence folder 37.


Constance Holden“Paul MacLean and the Triune Brain,” Science1979 204:1066–1068 p. 1068.


MacLean to Ardrey December 20 1971MLP Box 1 – Answered Letters folder 3. Published by Atheneum (NY) The Social Contract was the third part of a tetralogy started in 1961 with African Genesis. A Personal Inquiry into the Animal Origins and Nature of Man (1961) – a long time bestseller – followed by The Territorial Imperative. A Personal Inquiry into the Animal Origins of Property and Nations (1966) and ending with The Hunting Hypothesis. A Personal Inquiry Concerning the Evolutionary Nature of Man (1976).


Ardrey to MacLean March 13 1976MLP Box 1 – Answered Letters folder 3. In a letter dated February 22nd 1978 he exultantly believed to see around a “new pro-Ardrey gang headed by E.O. Wilson.” Ardrey died in 1980 and the MLP folder on him contains a message by the psychologist John Paul Scott to the senior editor of Readers Digest (probably forwarded to MacLean) with a merciless judgment on him: “You should place no faith in Robert Ardrey as a scientist. He had a little training as an anthropologist in his youth but his primary career was as a dramatist and later as a publicist. While he liked to portray himself as a scientist his actual method of thought was that of an advocate; that is he was concerned with making a case for his preconceived ideas” (Scott to Methvin September 11 1982 MLP Box 1 – Answered Letters folder 3).


Dart to MacLean February 12 1976MLP Papers – Answered Letters folder 27: see Raymond A. Dart “The Dual Structure of the Neopallium: its History and Significance” Journal of Anatomy 1934 69:3–19. MacLean to Dart March 25 1976 MLP Papers – Answered Letters folder 27. The proceedings of the Papez Symposium held at the University of Toronto (November 5–6 1976) as a satellite to the Sixth Annual Meeting of the Society of Neuroscience were edited by Kenneth E. Livingston Oleh Hornykiewicz Limbic Mechanisms. The Continuing Evolution of the Limbic System Concept (New York: Springer 1978). MacLean had been invited “as the one who picked up Papez’s torch and carried it and saw the implications before anyone else” (Livingston to MacLean October 2nd 1975 MLP Box 11 – Papez Symposium folder 26). His discourse opened the Symposium (Challenges of the Papez Heritage pp. 1–15). Dart continued to correspond with MacLean up until his death in 1988 at the age of 95. His letters express admiration for the work done at the Poolesville Laboratory which he had visited in 1976: “Let me also congratulate you on your magnificent effort in correlating the current data in cerebral evolution ethology animal behavior experimental neurology with human speech memory and learning in such a way as to be understood and appreciated […] You are the first medically-qualified and experimental neurologist as far as my antiquated knowledge goes to have directed your primate experimental studies specifically to the evolutionary significance of their past” (Dart to MacLean July 19 1978 MLP Box 1 – Answered Letters folder 27).


Paul D. MacLean“Putting On Our Thinking Caps,” New York TimesJanuary 1 1971:23.


Henry Allen“Beastliness. The Three Brains of Dr. Paul MacLean,” Washington PostFebruary 10 1974. The title of both of MacLean’s talks is Brain Mechanisms of Ancestral Behavior: MLP Box 11 – Gainesville March 17 1973 and Charlottesville May 11 1973 folders 4 and 6.


MacLean to Koestler November 20 1975MLP Box 3 – General Correspondence folder 37. A Festschrift for Koestler had just come out thirteen essays dealing with his multifaceted activity. The collection closed with an essay by MacLean on “The Imitative-Creative Interplay of Our Three Mentalities”; see Harris (ed.) Astride the Two Cultures (cit. note 48) pp. 187–213. MacLean sent the editor his “infinite praise for having created this beautiful testimonial to a man whose writings will stand out as unique in the history of letters” (MacLean to Harris September 15 1975 MLP Box 3 – General Correspondence folder 37).


Carl SaganThe Dragons of Eden. Speculations on the Evolution of Human Intelligence (New York: Random House1977) pp. 49–79.


MacLean to Sagan November 24 1982CSP.


Sagan to MacLean October 20 1981CSP. After having read Sagan’s West Point lecture MacLean hyperbolically eulogized him: “With its eloquent development it is easy to see why your audience was so enthusiastic. You are making a neo-Carlylian out of me! By that I mean that I am again beginning to believe in heroes and hero-worship!” (MacLean to Sagan June 17 1982 CSP).


Sagan to MacLean May 25 1982CSP.


Sagan to MacLean October 16 1983CSP. As for the amusing column see Sarah Overstreet “Man’s Slithery Nature Alive Well in the Brain” Good Life August 15 1983 inspired by a David Bottoms’ poem (“Crawling Out at Parties”) with the following incipit: “My old reptile loves the Scotch / The way it drugs the cells that keep him caged in the ancient swamps of the brain […].” However in the 1979 interview already mentioned Constance Holden had noted that despite Sagan’s amplification “MacLean is not one of those scientists whose work has captured the popular imagination” because of his virtually unique ethological approach to the human brain: see Holden “Paul MacLean” (cit. note 64) p. 1066.


Paul D. MacLean“Brain Evolution Relating to Family, Play, and the Separation Call,” Archives of General Psychiatry1985 42:405–417.


Paul D. MacLean“Women: A More Balanced Brain?,” Zygon. Journal of Religion and Science1996 31:421–439. Since 1973 MacLean had collaborated occasionally with Zygon and exchanged correspondence with its founder and editor Ralph W. Burhoe who once expressed his pleasure at having MacLean’s support “in the fact that our best wisdom and logic does not match the unconscious and unknown wisdom that men have” (Burhoe to MacLean July 7 1973 MLP Box 13 – Professional activities folder 13).


Paul D. MacLean“Brain Roots of the Will-To-Power,” Zygon. Journal of Religion and Science1983 18:359–374.


  • View in gallery
    Figure 1

    Medial view of the right cerebral hemisphere, showing the hippocampus and its connection with the mammillary body through the fornix and the connections of the mammillary body to the anterior thalamic nuclei and thence to the cortex of the gyrus cingulifrom James W. Papez, “A Proposed Mechanism of Emotion,” Archives of Neurology and Psychiatry, 1937, 38:727–743, p. 727

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    Figure 2

    The shaded area of cortex represents what was formerly known as the limbic lobe of Broca and subsequently termed the rhinencephalon by Turner. It corresponds to MacLean’s visceral brain.from Paul D. MacLean, “Psychosomatic Disease and the Visceral Brain. Recent Developments Bearing on the Papez Theory of Emotion,” Psychosomatic Medicine, 1949, 11:338–353, p. 340

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    Figure 3

    Representation of the hippocampal region. HYP indicates the anterior, middle, and posterior divisions of the hypothalamus. Directly above are the three subdivisions of the right anterior nucleus of the thalamus.from Paul D. MacLean, “Psychosomatic Disease and the Visceral Brain. Recent Developments Bearing on the Papez Theory of Emotion,” Psychosomatic Medicine, 1949, 11:338–353, p. 345

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    Figure 4

    A diagram indicating the anatomic and possible functional relationships of various parts of the hippocampal formation (which includes the hippocampal and dentate gyri, the hippocampus and the amygdala)from Paul D. MacLean, “Psychosomatic Disease and the Visceral Brain. Recent Developments Bearing on the Papez Theory of Emotion,” Psychosomatic Medicine, 1949, 11:338–353, p. 346

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    Figure 5

    Master plan of the site of the NIH Animal Center – October 18, 1964 (MLP, Box 6, folder 42)

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    Figure 6

    First visualization of the three brains. Color drawing attached to the typescript of a Brady lecture given by MacLean on January 7, 1965 at the School of Medicine of the Johns Hopkins University.


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