The life and career of Paul MacLean: A journey toward
neurobiological and social harmony
Kelly G. Lambert*
Department of Psychology, Copley Science Center, Randolph-Macon College, P.O. Box 5005, Ashland, VA 23005, USA
Received 4 April 2003; accepted 17 April 2003
Working as a physician, Paul MacLean’s interests moved in the direction of the brain when he realized that most of his patients suffered
from symptoms (e.g. anxiety, sleeping problems) that could not be traced to a known physiological cause. His curiosity about the
neurological origins of these psychological symptoms led him to the laboratories of Stanley Cobb and James Papez, both of whom were
influential in guiding MacLean’s interests toward the temporal lobe. His neurobiological interest was not contained, however, to the temporal
lobe. As his own family grew to include a wife and five children, his scholarly pursuits extended to social and familial relations and their
accompanying underlying neuroanatomical circuits (i.e. the thalamocingulate system). Viewing the brain and behavior from an evolutionary
perspective, MacLean introduced the concept of the ‘‘triune brain’’ to describe the evolutionarily distinct components of the mammalian brain
and reintroduced Broca’s term ‘‘limbic’’ to describe a neuroanatomical system involved in emotional functions. MacLean wrote that the
development of social behaviors, such as mother–infant audiovocal communication and the separation cry of the offspring, served as the
driving force in the evolution of the neocortex. MacLean’s neuroevolutionary perspective and appreciation of the complexity and
evolutionary significance of social systems offer valuable insights into the contemporary fields of behavioral neuroscience and biological
D2003 Elsevier Inc. All rights reserved.
Keywords: Triune brain; Limbic system; Paul MacLean; Neuroethology; Thalamocingulate division; Social neuroscience
According to Paul MacLean, social separation is one of
the most stressful events a mammal encounters in its
lifetime. Although other environmental events such as pain
or starvation offer more severe immediate risks to the
survival of an individual, MacLean perceives that the
removal of a conspecific results in an even larger emotional
response than these more obvious threats to survival. In fact,
MacLean places so much value on social and family
relations that he proposed that they played an integral role
in the direction of mammalian evolution. In the following
article, we will discuss the scholarly and personal journey
that eventually led MacLean to his pioneering work in the
area of social neuroscience. Notable career milestones such
as the evolution of the limbic system and triune brain
concepts will also be discussed. Finally, the legacy of Paul
MacLean’s career will be considered as we review the
impact of his work in the fields of behavioral neuroscience
and biological psychiatry.
2. Early life and career
Paul MacLean was born on May 1, 1913 in Phelps, NY.
He attended prep school for the sole purpose of attending
Yale University—following in his brother’s footsteps. Fol-
lowing graduation from Yale, he decided to study philoso-
phy with A.E. Taylor, a scholar of Plato, at New College,
Edinburgh. However, soon after making this bold decision,
MacLean started having second thoughts about his ability to
contribute to the body of philosophical knowledge that had
existed for centuries. Additionally, his mother became
seriously ill around this time. It was originally suspected
that she had a cardiovascular condition, but her physician
helped to discern that the actual problem was gallstones.
MacLean was fascinated with the physician’s diagnostic
skills and his mother’s subsequent recovery, so much so that
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E-mail address: email@example.com (K.G. Lambert).
Physiology & Behavior 79 (2003) 343– 349
he decided medicine would be a rewarding career. In 1936,
he commenced his medical training at Yale University
School of Medicine . Interestingly, MacLean’s personal
maternal relationship played a pivotal role in directing his
career toward medicine; as will be discussed later, this
interest in the maternal– offspring relationship would later
influence him as he theorized about the evolution of
MacLean was initially exposed to psychiatry when he
volunteered to be part of the Yale Unit during World War
II and was given a hospital assignment in Auckland, New
Zealand. When the resident psychiatrist disappeared, Mac-
Lean was promptly assigned to Psychiatry where he
encountered interesting interactions such as a patient at-
tempting to strangle him with his own necktie. These ex-
periences prompted MacLean to start thinking about the
origins of normal and abnormal behavior; however, this
early experience with psychiatry was not enough to moti-
vate him to alter his career path toward the field of
Following the war, MacLean and his wife moved to the
state of Washington where he opened a private practice.
MacLean became increasingly frustrated in this practice as
he realized that the majority of his patients’ symptoms were
psychological in nature, leaving him with a feeling of
incompetency because he had no idea where in the brain
these symptoms were generated. In an attempt to relieve this
frustration, MacLean reviewed the writings of Dr. Stanly
Cobb at Massachusetts General Hospital in Boston, con-
tacted him, and was subsequently invited for a fellowship
3. The evolution of the limbic system concept
After moving his three young boys to Boston, MacLean
embarked on a research project assessing the bioelectrical
activity of certain structures at the base of the brain. Because
of its reported role in emotions, MacLean was initially
interested in the hypothalamus. His first contact with the
brain tissue itself came when he designed nasopharyngeal
electrodes that could be slipped up the sides of the nose.
Working with patients suffering from psychomotor epilepsy,
MacLean noted the relationship between the structures of
the temporal lobe, especially the area around the hippocam-
pal formation, and emotional experiences reported by the
patients. But why was this structure involved in emotions?
Again, MacLean consulted the literature and was intrigued
by an article he discovered entitled A Proposed Mechanism
of Emotion written by James W. Papez in 1937 .
As MacLean read Papez’s description of an emotional
circuit, in which the hippocampal formation connected with
the hypothalamus, he knew that he was on the right track
toward understanding the neuroanatomy of emotions.
MacLean remained puzzled, however, about the relation-
ships between exterosensory information and the emotional
activation that he had observed in his epileptic patients.
Cobb suggested that MacLean visit Papez to discuss these
matters and, during the spring break of 1948, MacLean
traveled to Cornell to experience an intense 3-day tutorial in
comparative neuroanatomy with Papez . This visit was a
life-changing experience for MacLean as he was in awe of
the neuroanatomical skill of Papez, who pointed out how
visual, auditory and somatic sensory information entered the
hippocampal formation. Even today, 55 years following his
time with Papez, MacLean describes him as saint-like and
one of the most gifted neuroanatomists of the last century
. This work culminated in a publication entitled: Psycho-
somatic Disease and the ‘Visceral Brain’ in 1949 .
MacLean avoided referring to the circuit as the rhinenceph-
alon because he wanted to downplay the olfactory function
and emphasize the emotional function. He subsequently
decided to use the term visceral because of its original
16th century definition referring to strong inward feelings.
The significant aspect of this paper was MacLean’s sugges-
tion that mammalian brains may have a common feature of a
rather primitive system responsible for integrating sensory
information, suggesting a dichotomy between our intellec-
tual behavior and emotional, nonverbal, behavior .
Following his research fellowship in Cobb’s laboratory,
John Fulton invited MacLean to join the Department of
Physiology at Yale Medical School. During his tenure at
Yale, MacLean turned to Broca’s work and became espe-
cially interested in his descriptions of a ‘‘great limbic lobe’’
that surrounded the brainstem . Because Broca empha-
sized the limbic lobe’s role in olfaction, a function thought
to be of little importance to humans, this anatomical circuit
had become the unwanted child of brain anatomy books and
lectures. MacLean wrote that one author conveyed that this
area of the brain likely contributed very little to the
evolution of the human brain and, consequently, should
not be considered further in the text . After reviewing
Broca’s use of the term limbic, he felt that this term was
more appropriate than the term visceral and he began
referring to the emotional circuit as the limbic system
because this new term had only descriptive connotations
as opposed to the functional connotations associated with
the term visceral .
4. The evolution of the triune brain concept
As MacLean was becoming interested in the limbic
circuit, he was intrigued by a comment made by Rose
suggesting that the mesocortex made its first appearance
in mammals and was somewhat transitional between the
more primitive archicortex and the more recently evolved
neocortex (Ref.  reviewed in Ref. ). MacLean later
conducted a study with rats in which he showed differential
uptake of S-labeled L-methionine among the archicortex,
mesocortex and neocortex areas—a finding that he felt
distinguished the limbic cortex from the neocortex .
K.G. Lambert / Physiology & Behavior 79 (2003) 343–349344
While at Yale, he continued to conduct research discerning
the neuroanatomical boundaries and characteristics of the
areas comprising the limbic circuit.
In 1956, MacLean was awarded an NSF senior postdoc-
toral fellowship at the Institute of Physiology at the Univer-
sity of Zurich. Upon returning, he was invited to join a new
lab section at the National Institute of Health that was
subsequently named The Section on Limbic Integration and
Behavior. He joined the NIH in 1957 embarking on a career
that he would cherish until his current state of semi-retirement
(he continues to visit a modest lab and office at NIMH). The
primary purpose of this laboratory was to investigate the
electrophysiological and anatomical aspects of the limbic
cortex and its multiple associated sensory systems. In order to
do this, MacLean turned to a squirrel monkey model and
employed the help of the German psychiatrist Detlev Ploog,
who had specialized interests in ethology, to help establish an
ethogram for these animals [1,9].
MacLean first publicly discussed his idea of the triune
brain in 1969 when he delivered a series of lectures at Queens
University in Kingston, Ontario (Ref.  reviewed in Ref.
). He explained that the formidable cortex of humans
evolved while retaining three basic formations delineating its
ancestral relationship with reptiles, as well as early and more
recent mammals. He argued that one may perceive humans as
having three different brains in one with each ‘‘brain’’ having
a distinctive set of capabilities. He later wrote:
Man, it appears, has inherited essentially three brains.
Frugal Nature in developing her paragon threw nothing
away. The oldest of his brains is basically reptilian; the
second has been inherited from lower mammals; and
the third and newest brain is a late mammalian
development which reaches a pinnacle in man and
gives him his unique power of symbolic language. This
can be said with some assurance, because the big brain
which sits on top has been more thoroughly inves-
tigated than the other two. (, p. 96)
Much to MacLean’s surprise, the notion of this multifac-
eted brain became wildly popular in the press. The media,
however, overemphasized MacLean’s suggestion that we are
under the control of three very different brains, failing to
convey his ideas that these components contribute to a
single, functioning brain. This confusion led him to search
once again for a more defining term to use. Because triune
literally means three-in-one, he chose that term for his new
evolutionary brain theory . Considering that MacLean’s
father was a Presbyterian minister, this term seemed perfect
for his theory at the time, but he later regretted this choice
due to its religious connotations .
MacLean expanded his neurobehavioral investigation of
the triune brain to a larger repertoire of species when NIH
completed a satellite field laboratory just south of Pooles-
ville, MD in 1971 [1,3]. It was here that MacLean began his
studies with reptiles, namely, the Komodo dragon, and
discovered that mammals and reptiles share a common base
of basic behaviors consisting of behaviors such as daily
routines and subroutines and the displays associated with
social communication . These studies convinced Mac-
Lean that, whereas the mammalian brain was more advanced
than the reptilian brain, the mammalian brain retained the
primitive aspects of the reptilian brain. Human cases, in
which a relentless murderer stalks his/her next victim,
convinced MacLean that the reptile was at work in the
human brain . MacLean’s work also directed him to
the ‘‘basal ganglia and company’’ (as he described them in an
interview ) as the neuroanatomical site for this ancient
reptilian neuroanatomical complex (also known as the R-
complex). More advanced behaviors associated with both
self-preservation and survival of the species (e.g. the addition
of affect associated with basic survival behaviors and de-
creased tendency to cannibalize offspring) appeared along
with the appearance of the limbic structures . The most
recent mammalian brain is characterized by the thalamocin-
gulate division with numerous connections between the
cingulate mesocortical areas and the anterior thalamic nuclei
(among other thalamic areas ). There appears to be no
neuroanatomical corollary to the thalamocingulate division
in the reptilian brain—making it uniquely mammalian. As
discussed in the next section, this brain area is involved in
more advanced social behaviors such as communication (see
Fig. 1 for illustration of MacLean’s triune brain).
Fig. 1. A recent interpretation of MacLean’s triune brain emphasizing the
reptilian brain (hindbrain), the paleomammalian brain (limbic system) and
neomammalian brain (neocortex). Because MacLean emphasized the role
of the maternal – infant relationship, the brain is situated inside a maternal
squirrel monkey, a species that MacLean used extensively in his
neuroethological research (artwork by Jacqueline Berry, design by Kelly
K.G. Lambert / Physiology & Behavior 79 (2003) 343–349 345
5. A mother’s hand rocks the evolutionary cradle
With the discovery of the uniquely mammalian neuro-
anatomical circuit, namely, the thalamocingulate system,
MacLean once again allowed his interest in the maternal –
offspring relationship to direct his scholarly and profession-
al interests. According to MacLean, the three behaviors that
separate mammals from other vertebrates include (1) nurs-
ing, conjoined with maternal care; (2) audiovocal commu-
nication for maintaining mother – offspring contact; and (3)
play behavior (, p. 269). In fact, MacLean included an
entire chapter on this circuit and family-related functions in
his book (The Triune Brain In Evolution: Role in Paleo-
cerebral Functions ) entitled Participation of thalamo-
cingulate division in family-related behavior. In this chapter,
MacLean emphasizes the profound importance of social
relations in the evolution of the brain by arguing that the
prolonged separation of the offspring from its nursing
mother results in fatal consequences for the developing
mammal. He proposed that the separation cry that enables
the mother to locate her lost offspring might have been one
of the first examples of mammalian vocalization . Cor-
roborating this theory of the separation cries being associ-
ated with the limbic circuit, MacLean, working with John
Newman (Child Health Laboratory of Comparative Etholo-
gy), found that the ablation of parts of the medial frontal
cortex in squirrel monkeys, specifically a portion of the
pregenual cingulate cortex and its extension to the subcal-
losal cingulate cortex, resulted in an elimination of the
spontaneous separation cry .
In an article entitled Women: A More Balanced Brain ,
MacLean continues with his scholarly interest in the moth-
er’s role in evolution. He wrote, ‘‘For more than 180 million
years, the female has played the central role in mammalian
evolution’’ (, p. 422). Additionally, MacLean proposed
that it was mothers who directed our species toward right-
hand dominance as they held their babies near their hearts so
that their heart rates would calm the baby—and subsequent-
ly relied on their right hands to manipulate environmental
surroundings. He felt that carrying infants might have also
influenced the anatomical and functional expansion of the
right hemisphere in women. Such evolutionary expansion
might have led to a more balanced brain, prepared for the
multitasking demands of caring for offspring . Related to
this observation, MacLean wrote:
...I will draw upon findings of continuing research that
provide both anatomical and functional evidence that
the minds of women sail in a vessel less tilted to the left
than do those of men. (, p. 422)
MacLean also noted subsequent neuroimaging research
documenting more interhemispheric activity in women
compared to men who exhibited more prevalent intrahemi-
spheric activity . Other supporting research comes from
an analysis of the planum temporale (PT), a brain area
hidden in the Sylvian fissure that is thought to be involved
in verbal associations related to hearing. Although original
reports suggested that the PT was larger in the left hemi-
sphere , upon a more specific analysis of gender differ-
ences, it was discovered that the left hemisphere dominance
was only apparent in the male brains—the PT was most
often larger in women’s right hemisphere .
Additionally, MacLean hypothesized that maternal com-
munication with her offspring, complete with fundamental
mammalian vowel and consonant sounds, served as the
originating point of speech . Although it was once thought
that a baby’s babbling was a mere exercise of the mouth’s
muscles, it is interesting to note that recent research suggests
that babbling responses are indeed generated in the left
hemisphere, as is language .
Thus, as vertebrates evolved from the nonmaternal,
sometimes cannibalistic, reptiles—that rarely offered more
directive maternal care than merely laying eggs—to mam-
mals such as squirrel monkeys that carry their offspring
almost continuously for months to years, the thalamocingu-
late portion of the brain expanded in accordance with this
family-centered neurobehavioral transition . The fact that
this thalamocingulate division is not apparent in the reptilian
brain reinforces its role in the mammalian family-related
behaviors . Additionally, with the observations that the
rostral cingulate cortex has been implicated in the off-
spring’s production of the separation cry, MacLean estab-
lished a link between the evolutionary significant separation
cry, a behavior important in maintaining maternal–offspring
relations, and the mammalian thalamocingulate division.
With such a valuable evolutionary investment depending
on the effective processing of this vocalization, it is likely
that subsequently evolved mammals became increasingly
prepared to respond to both the separation cry and emerg-
ing, more specific vocalizations. Hence, the genesis of more
complex communication processes [3,9,12].
6. The neuroscience of social harmony
As mentioned above, MacLean also noted the emergence
of play in the behavioral reportoire of mammals. Reinforc-
ing the notion that this behavior is mediated by the cingulate
portion of the limbic system, hamsters with cingulate lesions
appeared normal on every account except for the fact that
they did not engage in play behavior with their littermates.
Speculating on the function of play, MacLean has written
that it might have evolved to promote social harmony in the
nest and, as the animal matures, social affiliation .
Ironically, the evolutionary predisposition to maintain
social harmony, or even a family way of life, comes with
the cost of drastic repercussions when the social harmony is
interrupted by social separation. As discussed in the opening
statements of this article, MacLean conveyed that nothing
brings more pain to a mammal than being separated from its
own kind. MacLean suggested that this is the case because
the cortical area underlying the separation cry is partially
K.G. Lambert / Physiology & Behavior 79 (2003) 343–349346
innervated by the thalamic nuclei that are involved in pain
perception. Accordingly, small doses of morphine have been
found to eliminate the cry . Thus, when mammals
became family oriented, they became a target for one of
the most distressing forms of suffering—social separation
and isolation . Because, according to MacLean, this
social dependence evolved in synchrony with the mamma-
lian female’s maternal responses, the female brain may be
more empathetic than the male’s brain. Further, the social
responsibility toward her offspring seemed to be a step up
the ladder to humanity as the maternal animals extended
care to nonfamily members and began to develop a sense of
social conscience. This highly evolved thalamocingulate
division is also responsible for humans being the first
species to not only care if our own species lives or dies,
but to extend that concern to other species [1,3].
In an interview with Constance Holden for Science in
1979 , MacLean was quite optimistic about the har-
mony of the human race—especially if we could maximize
the use of one of the destinations of the limbic system’s
thalamocingulate circuit, namely, the prefrontal cortex.
Unique to humans, abilities such as foresight and insight
merge to create empathy and altruism, where the bound-
aries between the well-being of self and others start to fade
and become dependent on one another. In a recent inter-
view , MacLean’s optimism had waned after the horrific
tragedies occurring in the United States on September 11,
2001—a tragedy designed by the uniquely human cortex.
However, as separation cries were heard across the country
as loved ones were declared missing, and eventually
deceased, the tendency of U.S. citizens to reach out to
each other instead of running to safety in isolation was
striking—and predictive from MacLean’s writings about
the familial tendencies of the thalamocingulate division of
the limbic system.
7. The legacy of Paul MacLean ˙ ˙ ˙ and lessons learned?
7.1. Reaction to The Triune Brain in Evolution
It is difficult to imagine a scientist who has embarked
on more groundbreaking topics of such profound impor-
tance to the human species than Paul MacLean. His work
culminated in his publication of The Triune Brain in
Evolution: Role in Paleocerebral Functions in 1990 .
After spending 30 years writing this comprehensive vol-
ume, it was finally out for the public to read and review.
Considering the attention MacLean’s work attracted from
outside the mainstream science venues, such as Carl
Sagan’s utilization of the triune brain concept in his book
entitled The Dragons of Eden , the fields of neurosci-
ence, psychiatry and psychology have been a bit more
cautious about embracing his theories. As described by
Gerald Cory , MacLean received critical reviews in two
prominent scientific journals, Science  and American
Scientist . Focusing on the Science review , Anton
Reiner, a recent graduate in the field of neuroscience at the
time, was critical about several basic premises of the book.
For example, he criticized MacLean’s triune brain concept
for being outdated and his limbic system concept for being
out of step with the current evidence (current as of 1990)
that the hippocampus seemed to play a sole function in
memory. Cory  subsequently defended the scholarship
of MacLean by systematically addressing the criticisms
raised in the Science review. The American Scientist review
 was a briefer account but resembled the issues raised
by Reiner. Unfortunately, because readers usually prefer
reading a brief review as opposed to an entire book, the
negative reviews had a sizeable impact on the scientific
community’s reluctance to embrace MacLean’s meticulous-
ly documented book.
In spite of MacLean’s misfortune with book reviews, his
ideas remain valued by many in the field today . The
notion of the limbic system remains a popular classification
of the cluster of brain areas involved in emotional process-
ing. His ideas concerning the importance of social bonds
have shed light on possible mechanisms of mental disor-
ders such as autism, a disorder of social functioning.
Specifically, neuroanatomical studies of individuals diag-
nosed with autism point to inappropriately developed
limbic structures, namely, the amygdala and hippocampus
7.2. Neuroethological approach to the mind
MacLean’s interest in the development of a neuroetho-
logical approach to understanding mental experiences is
slowly growing acceptance as a legitimate and informative
perspective in several mental health disciplines such as
psychiatry, psychology, neuroscience and neurology. Along
these lines, a book entitled Darwinian Psychiatry  was
recently published documenting the value of understanding
the evolutionary context and function of certain behaviors.
Although his neuroethological approach to the ‘‘mind’’ has
been slow to gain mainstream acceptance, MacLean’s the-
ories explain many puzzling human behaviors ... such as
why the President of the United States might risk his career
by engaging in the more familiar behaviors of the R-
complex; or why certain individuals with no violent history
seem to ‘‘snap’’ and commit uncharacteristic acts of crime
(perhaps due to an epileptic – limbic type of seizure ); or
why surgeries interrupting the communication between the
striatum and cingulate cortex relieve some of the compul-
sive behaviors (or R-complex master routines) observed in
Obsessive– Compulsive Disorder ; or why infants de-
prived of their mother’s nurturing care and forced to live in
neglectful orphanages sometimes develop subsequent social
dysfunction ; or, finally, why, as children’s worlds
become more dominated by socially isolated endeavors
such as viewing television or interacting with a computer,
and more traditional social play becomes a fading compo-
K.G. Lambert / Physiology & Behavior 79 (2003) 343–349 347
nent of elementary school curricula, that an increasing
number of children are suffering from cognitive and behav-
ioral disorders (e.g. ADHD) .
Also important in the development of MacLean’s neuro-
ethological approach was the inclusion of several species—a
true comparative biopsychological approach. Toward this
goal, MacLean worked with humans, peacocks, squirrel
monkeys, rats, hamsters, anolis lizards and even komodo
dragons, as he disentangled the more primitive common
behaviors shared by all vertebrates. In keeping with Mac-
Lean’s neuroevolutionary perspective, contributions in this
special edition consist of research conducted on humans,
nonhuman primates, rats, mice, lizards, prairie voles and
tree shrews. As species such as the tree shrew are being
viewed as living fossils for more recent neomammalians, it
is likely that future comparative research may provide
additional evolutionary insights into the origins, mainte-
nance and functions of various behaviors.
7.3. Maintaining an appropriate neurobiological perspec-
One of MacLean’s most consistently reinforced themes
included his desire to consider both the ‘‘big picture’’ of
neurobiological functions as well as the more fine-tuned
cellular approaches when investigating the neurobiological
foundations of certain behaviors and mental functions. In
fact, MacLean recently claimed that the most unfortunate
event that ever occurred in the history of biological psychiatry
was Camillo Golgi’s discovery of a new technique to stain
neurons because neuroscientists tackled the microstructure
questions and abandoned their curiosity concerning the
systems of the brain . Although MacLean remains pas-
sionate about neuroanatomy, likening viewing the brain
through the microscope to ‘‘walking in a cathedral,’’ he
adamantly proclaims that structures are located in the brain
to build circuits and scientists should also be interested in
learning more about these circuits and the behaviors they
control . Accordingly, he wrote:
...starting with the subjective self as its province (its
territory), the domain of evolutionary psychiatry
encompasses both the microscopic and macroscopic
aspects of all the underlying phenomena as they seem
to unfold in past– present – future and relate to the
cosmos. (, p. 219)
Corroborating MacLean’s value of the more encompass-
ing evolutionary perspective, Jaak Panksepp recently con-
veyed his concern for a neuropsychiatry that emphasizes
molecular interactions while ignoring evolutionary issues,
claiming that this approach represents a scientific short-
sightedness—often missing the functional forests for the
more molecular undergrowth. In spite of MacLean’s attempt
to emphasize the importance of investigating both the
functional forests and the molecular details in order to arrive
at a more thorough understanding of the nervous system, a
more balanced approach is long overdue .
7.4. Establishing and maintaining professional and person-
In sum, Paul MacLean’s list of accomplishments
throughout his career are quite distinctive ... ranging from
the contributions of important concepts such as the limbic
system and the triune brain to his tenure as the Chief of the
NIH’s Laboratory of Brain Evolution and Behavior. As he
approaches his 90th birthday (see Fig. 2), he is doing
anything but resting on his laurels—continuing to struggle
with the big questions such as the meaning of life, the
evolutionary origins of tears of grief and tears of laughter,
the place of the family in the history of evolution and why
humans continue to optimistically bring children into a
world filled with uncertainty and violence [1,3]. He con-
tinues to frequent a small office at NIH where he works on
a project he affectionately calls the ‘‘5000 year project’’ in
which he is busy investigating even more connections
among the systems of the triune brain, hoping to further
delineate the harmonious connections among the many
circuits of the brain. He remains fascinated by the relation-
ship between a musical experience and an emotional
experience as he frequently uses emotional terms to de-
scribe musical ability, claiming that his gifted grandson can
make a piano ‘‘weep’’ and musical terms for emotional/
Fig. 2. Paul MacLean in his home in the spring of 2001 (photo by Kelly
K.G. Lambert / Physiology & Behavior 79 (2003) 343–349348
limbic observations as he likens the lines on a music sheet
to layers in the neomammalian cortex, or claims ‘‘that the
human brain can not be made to dance to any tune by
simply delivering a single drug...’’ . Further, he
sometimes finds himself speculating that something akin
to the phenomenon of a musical experience—a phenome-
non likely rooted in the basic rhythmic patterns of the R-
complex yet branches into the advanced thoughts of the
neocortex—may serve as an interesting model or analogy
for understanding emotional experiences [3,9]. Just as
music adds meaning to the rhythmic patterns of the R-
complex, stimulation of the prefrontal area ultimately adds
relevancy and meaningfulness to more basic emotional
stimulation originating in this area. Thus, harmony seems
to be a word that captures the life and career of Paul
MacLean. He attempted to define harmony among the
evolutionarily distinct sections of the mammalian brain as
well as establish harmonic relations among the micro and
macro circuits of the brain. MacLean’s most valued endeav-
ors, however, comprise the fruits of his own thalamocingu-
late neuroanatomical division as he enjoys the social
harmony provided by his wife, five grown children, eleven
grandchildren, and cherished colleagues.
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developments bearing on the Papez theory of emotion. Psychosom
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 Broca P. Anatomie comparee des circonvolutions decerebrales. Le
grand lobe limbique et la scissure limbique dans la serie des mammi-
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 MacLean PD. The triune brain in evolution: role in paleocerebral
functions. New York: Plenum; 1990.
 Rose M. Gyrus limbicus anterior and Regio retrosplenialis (Cortex
holoprotoptychos quin-questratificatus). Vergleichende Architektonik
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