HOW LITTLE WE
KNOW……….OR DO WE?
THE PHYSIOLOGY OF ROMANTIC LOVE
BY
MARC PETTY CRUCIGER, M.D.
PRESENTED TO THE CHIT-CHAT CLUB
SAN FRANCISCO, CALIFORNIA
APRIL 2007
PREFACE
“How Little
We Know”
How little we know, how much to discover
What chemical forces flow, from lover to lover.
How little we understand what touches off that tingle.
That sudden explosion when two tingles intermingle.
Who cares to define what chemistry this is?
Who cares with your lips on mine. How ignorant bliss is.
So long as you kiss me and the world around us shatters
How little it matters. How little we know.
How little we know. How little we know.
Composers: Carolyn Leigh and Phillip Springer
Singer: Frank Sinatra
Arranger: Nelson Riddle
Good evening gentlemen.
2400 years ago, on a night much like
tonight, a group of distinguished Athenian gentlemen got together for a dinner
and drinking party. Before the party had
progressed very far, one of the guests suggested that the evening be spent on a
subject not commonly discussed by them.
Tonight, I suggest we do the same. Tonight, gentlemen, we shall speak of
love.
But, gentlemen, of what kind of love shall
we discuss? All of us know that
there are many kinds of love. The Greeks
had different words to describe them. Agape was used to describe
unselfish, all-giving, spiritual love. Storge
was used to mean natural affection like parental love. Philia
was used to describe a non-sexual, brotherly love. But these are not the kinds of love I wish to
discuss. Tonight I want our attention to turn to what the Greeks called eros. This is
romantic love…the love that describes a passionate and erotic, all consuming
desire, both physical and emotional, for a very specific partner. This is the kind of love that has obsessed
men and women since Adam and Eve. It has
inspired poets, writers, and musicians down through the ages and across all
cultures.
To be specific, however, tonight I want to
explore what really happens physiologically to us when we fall in love. Interestingly, there were attempts to
understand the physiology of romantic love down through the ages. In the western intellectual world, Plato was
the first to try but the baton was soon passed to the medical world where it
would remain for the next 2000 years.
Because of the scientific revolution in medicine, the subject was
essentially abandoned by the early 20th century. But, within the past two decades, there has
been a resurgence of interest and subsequent scientific research. And, as I shall argue this evening, the
ancient scientific understanding of the physiology of romantic love showed a
prescience that is simply astonishing with today’s understanding. But in order to substantiate my hypothesis, I
must first acquaint you with what the ancients believed happens when you fall
in love.
The first attempt in the western
philosophical tradition to understand the nature of love is found, of course,
in Plato’s two great Socratic dialogues: the Phaedrus and the Symposium. In the Phaedrus, Socrates tells us
that love is a “sort of madness”(1) given to man as a
“gift of the gods”(2). He continues by
saying that when one is in love he is “touched by … madness”(3). In the Symposium, Socrates tells the
assembled gentlemen at the dinner party that he has learned that love is always
“needy”(4).
Plato writes again in the Phaedrus:
In this state of mingled pleasure and pain
the sufferer is perplexed by the
strangeness of his experience and struggles helplessly; in his frenzy he
cannot sleep at night or remain still by day, but his longing drives him
wherever he thinks he may see the possessor of beauty.(5)
All of us around this table
will recall that, for Plato, eros is
ultimately a bridge that leads the lover on a transcendental journey to an
understanding of ultimate spiritual beauty.
But let’s make no mistake about it, gentlemen, Plato emphasizes that
love is something that begins very viscerally…a psycho-physiologic human need
or drive if you will, that leads to a sort of madness.
This concept of love being a state where
one is out of control and exhibiting physical symptoms is articulated by one of
the greatest love poets of the early Western tradition, Sappho. Gentlemen, let us listen to Sappho as she
describes romantic love in the following fragment:
For
I only, briefly, need glance at you to
Find my voice has gone and my tongue is broken,
And a flame has stolen beneath my skin, my
Eyes can no longer
See, my ears are ringing, while drops of sweat run
Down my trembling body, and I’ve turned paler
Than a wisp of straw and it seems to me I’m
Not far off dying.(6)
Burning skin? Eyes that do not see? Pallor? Ringing in
the ears? Madness? Trembling? Inability to speak? It really seems as if Plato and Sappho are
describing symptoms of some sort of disease?
And, indeed, as Dr. Frank Tillis writes in his
book, Love Sick: Love as a Mental Illness:
Love is…associated with a wide range of
physical ‘symptoms’. Lovers are often
described as fevered, or pale and depleted—unable to sleep or eat…for as long
as people have been writing about love, they have also been describing it as an
illness.(7)
Paradoxically, although many of the
symptoms of love do mimic those of an illness, there was a surprising lack of
medical writing on the nature of love until we meet the great doctor of Roman
antiquity, Galen. In his book, On
Prognosis, Galen is called upon to cure Iustrus’s
wife of insomnia. Although the woman was
not helpful in answering questions as to her medical problem, Galen noted that
when the name of a dancer, Plyades, was mentioned in
her presence, her “expression and complexion changed” (8) and her “pulse became
extremely irregular.”(9) The symptoms
did not occur with the names of other dancers.
Gentlemen, let us listen to Galen on perhaps the very first medical
diagnosis of love in the Western tradition:
On the fourth evening, I kept very careful
watch when it was announced that Plyades was dancing.
And I noticed that the pulse was very much disturbed. Thus I found out that the woman was in love
with Plyades, and by very careful watch on the
succeeding days my discovery was confirmed. (10)
Galen was profoundly influenced by the
ancient Greek model of disease that traditionally has been attributed to
Hippocrates, the father of medicine.
Hippocrates and his followers postulated that all disease was simply an
imbalance of four bodily humours: yellow bile, black
bile, blood and phlegm. (Figure 1) Using this scientific framework, Galen
hypothesized that romantic love, because of its physical symptoms, could be
understood physiologically using the Hippocratic humoural
model. Galen jettisoned the Platonic
model, hypothesizing that when one falls in love, the body’s four humours become unbalanced causing the symptoms one sees in
lovers in love. Dr. Tallis summarizes:
Galen was happy to follow the Hippocratic tradition…The symptoms of love were nothing to
do with divine intervention. He proposed
that the lovesick individual, under the influence of a strong passion,
experiences a humoral (or chemical) imbalance, which
in turn promotes the occurrence of physical symptoms. (11)
With the fall of the Roman empire and
Europe’s entry into the Dark Ages, subsequent scientific inquiry on romantic
love was passed on to the intellectuals of the Arabic speaking world. As they rediscovered the classical writings
of Hippocrates and Galen, Muslim physicians readily embraced the Greek paradigm
for the understanding of disease. One of the greatest Arab physicians of the
medieval period was Ibn Sina,
originally from Iran. In his book, The
Canon of Medicine,
Ibn Sina
(980-1037 CE) agreed with Galen. Ibn Sina writes that the symptoms
of love sickness are due to “the result of a chemical imbalance brought about
by…obsessing about the loved one.” (12)
As Europe slowly emerged from the medieval
period and rediscovered the classical tradition, the physiological
understanding of romantic love being caused by an imbalance of the four basic
body humours persisted. In Elizabethan England, there was even an
attempt to understand why romantic love was more common in the young as
compared to the aged using the humoural model. In the book, Not Wisely but Too Well:
Shakespeare’s Love Tragedies, the author Franklin Dickey explains the
Elizabethan theory as follows:
…in youth the sanguine humor,…hot and moist,
was at its peak; since love gained its mastery by heating the blood, the young,
whose blood was hot, were amorous…the old on the other hand, whose temperament
was usually dominated by cold and watery phlegm, (and) naturally were able to
resist the heat of love more readily (than) could the young. In middle age… the blood was usually tempered
with more of the cold humors, black bile… and phlegm. Love could not readily cause…excessive heat....(13)
As we all know at this table, from the
middle of the 16th century through the late 19th century, European scientists
began to chip away at the ancient Greek humoural
model of understanding disease. New
findings in anatomy by Vesalius as well as Harvey’s discovery of the
circulation of the blood were like battering rams on the established theory.
(14) Thomas Willis’s book, The
Anatomy of the Brain in 1664, also served to undermine the old foundation
because he argued that “psychological problems previously attributed to either
supernatural or humoural causes were, in fact, the
result of neurological abnormalities.” (15)
In the 1800’s when germs were shown to be the cause of many diseases,
the old humoural system of understanding disease
essentially crumbled. Preoccupied with
understanding and treating physical disease, the world of emotions was relegated to
a new medical discipline called psychiatry.
Freud, psychiatry’s earliest and most
prolific theorist, argued that the sexual drive was one of the most basic human
motivators. He termed it Eros or life
drive. But for Freud, human romantic
love was all about sex. As Dr. Tallis points out:
It is now widely accepted that Freud had
little to say about love, largely because of his preoccupation with sex. In
Freud’s scheme, love tends to be viewed as a secondary…by-product of frustrated
libidinous urges.(16)
Because of Freud’s huge
influence, psychiatry concerned itself very little with the phenomenon of
romantic love. Psychiatry’s cousin,
psychology, also did the same. In a 1958
presidential address to the American Psychological Association, its president,
Dr. Harlow stated the following:
So far as love or affection is concerned,
psychologists have failed in their mission.
The little we know about love does not transcend simple observation, and
the little we write about it has been better written by poets and novelists.(17)
Yes, gentlemen, as mentioned at the
beginning of this paper, by the mid 20th century there was no real
physiological understanding of romantic love because the modern scientific
world had simply decided to ignore it.
2000 years of cogitation had brought us back to our writers, poets and
musicians. Perhaps, Dr. Harlow should
have asked Sinatra to summarize the crux of his address by singing the song
“How Little We Know” at that meeting in 1958.
However a nearly contemporaneous discovery
was made that had profound effects in all fields of medicine. That discovery was the elucidation of the
structure of DNA by Watson and Crick, and, with it, a modern renaissance in
basic biological and medical research was begun. The new field most germane to
our discussion tonight is that of neuroscience that developed using the tools
from biochemistry, molecular biology, and physics. This new discipline seeks to understand the
chemical and dynamic workings of the brain.
Bioassays of neurotransmitters and new methods of imaging the brain,
both in its static state and in its functional state, developed so, that within
the past twenty years, the tools were finally in place to allow researchers to
take a new and serious look at the physiology of that most human subject,
romantic love.
Now, gentlemen, I want to share with you
what the neuroscientists have discovered recently about the physiology of
love. And, as I mentioned in the
beginning of this paper, I believe it can be argued that the ancient
physiological understanding of what happens when one falls in love is extremely
close to the new modern understanding, namely that love is a human drive or
need caused by an imbalance, not of humours, but of
hormones and neurotransmitters that work in very specific parts of the
brain. Let us take a look at the
findings of this new research.
LUST, ROMANTIC LOVE, and LONG TERM ATTACHEMENT
Helen Fisher, in her book, Why We Love:
the Nature and Chemistry of Romantic Love, argues that love can best be
understood physiologically if it is broken down into three stages or phases
of behavior: (1)Lust, (2) Romantic
love, and (3) Long Term Attachment. As all of us at this
table know, these phases are not mutually exclusive. For example, you can have a long term
attachment with your spouse but still experience lust for another person. Although I have chosen the area of romantic
love for tonight’s discussion, for completeness sake, let us look at all three
individually.
I. LUST PHASE
The first stage is LUST. This is the primordial drive for sex and is
essentially driven by levels of the hormone testosterone. Both genders have
testosterone, males, obviously, have more of the hormone. As testosterone levels increase, sexual
desire increases and vice versa. Male
libido tends to peak in the 20’s and decline during middle and old age. Women’s libido, although not as high as men’s,
does not statistically decline in middle age because as estrogen levels diminish,
it unmasks the latent testosterone hormones. (18) Lust does not seek a mate but a physical
encounter.
II. ROMANTIC LOVE PHASE
ROMANTIC LOVE is the phase of love
that Plato called “a madness”. It makes us giddy and gives us high energy and
causes obsessive behavior. The current
research has shown that individuals in the stage of romantic love have
unusually high levels of several chemicals.
They are (1) phenylethylamine, (2) dopamine,
and (3) norepinephrine. What do each of
these chemicals do to us? In short, they
produce in us the symptoms observed and experienced in those who are madly and
passionately in love. Gentlemen, now
let’s briefly look at each of these chemicals one at a time that are associated with romantic love.
Phenylethylamine,
or PEA for short, is often referred to in the lay press as the “love
molecule.” It is essentially a natural
form of amphetamine that our body produces.
The molecule is thought to speed up the flow of information between
nerve cells. Writers of romantic love often describe lovers as being shaky,
prone to insomnia, as well as having increased energy and poor appetite. Increased respiration and heart rate are also
common when one is near the one the lover desires. As Elvis Presley sang, when one is in love,
one really is “all shook up.” This
physiological state is caused by high levels of PEA. Interestingly, one sees similar symptoms in
people who are high on amphetamines.
High levels of the chemical PEA have been well documented in people who
are in the initial throws of the romantic infatuation phase of love. But, PEA levels do tend to diminish over
several years after one “falls in love”. (19)
The second and most important chemical
that researchers have found elevated in romantic love is dopamine. It is a member of the chemical family that is
the precursor to epinephrine, often called adrenaline by laymen. In the brain,
dopamine acts as a neurotransmitter. It
is also a neuro-hormone released in the part of the
brain called the hypothalamus. Dopamine
is important in allowing the body to move.
A shortage of dopamine causes Parkinson’s disease. But dopamine also, as Dr. Crenshaw states,
“…mobilizes you to recognize, seek and pursue pleasure.” (20) The new research on love has shown that
dopamine is elevated in those smitten with love. In addition, dopamine stimulates sexual
desire by raising testosterone levels.
For that reason, Dr. Fisher refers to dopamine as the “liquor of
romance.” (21) Dr. Crenshaw elaborates
further:
Dopamine takes you on an emotional high…it is
especially desirable and addictive…(it) is the common denominator in most human
addictions from drug abuse to hypersexuality…(22)
In short, the “high of love”
is physiologically very similar to the high of drugs such as amphetamines and
cocaine.
Closely related to dopamine is the third
romantic love chemical called norepinephrine
also a form of adrenaline. It is
produced in the adrenal glands. It is
also a neurotransmitter in the brain.
Like PEA and dopamine, norepinephrine also
increases testosterone levels. This chemical is a stimulant and lower brain
levels of it seem to be correlated with depression. We all know,
gentlemen, smitten lovers have high energy levels and are exhiliarated. Just recall Oscar Hammerstein’s lyrics in the
song “Hello Young Lovers”:
I know how it feels to have wings on
your heels
and to fly
down the street in a trance,
You fly down the street in the chance
that you meet
and you meet,
not really by chance.
This sensation of “wings on your
heels” may be due to norepinephrine’s stimulation of
the sympathetic nervous system. As Dr.
Fisher states, “…increasing levels of this simulant
generally produce exhilaration, excessive energy, sleeplessness, and loss of
appetite—some of the basic characteristics of romantic love.” (23)
As you can see, gentlemen, the new
research on the physiology of love actually supports the Hippocratic model,
namely that when one is in love, there is a change or imbalance in chemical
levels, specifically in the brain. Once
one finally finds that special someone and falls in love, the levels of phenylethylamine, dopamine, and norepinephrine
increase as compared to the levels in those not in the throws
of romantic love. All of these three
chemicals have the further hormonal effect of raising testosterone levels
thereby increasing libido. As all these “love potion juices” flow, they cause
the symptoms and behavior of those who are smitten with love.
Research has gone even further. Using the new technology of functional MRI,
neuroscientists are able to visualize which parts of the brain are active at
any given time. And the critical
question that needed to be answered is the following: Are the areas of the
brain associated with the dopamine centers more active in those individuals in
love than those who are not in love? The
short answer is a resounding “yes”!
In the year 2000, two distinguished British
neuroscientists, Bartels and Zeki, performed
functional MRIs on 17 students who reported being madly in love. The study
compared the MRIs when the lovers were shown pictures of the faces of their
lovers in contrast to the MRIs taken when they were shown faces of just their
friends. The results showed that when the subjects were shown their beloved’s
face, the area of the brain called the caudate nucleus “lit up”. (Figure
2) And, gentlemen, the
caudate nucleus is the area where 80% of the brains receptors sites for
the neurotransmitter dopamine reside. Of
note, it is also the area of the brain that is involved with cocaine and drug
induced euphoria. The researchers concluded
something that all lovers know, namely, that there is “…a close neural link
between romantic love and euphoric states.”(24)
Importantly, the study also showed that
the areas of the brain activated in romantic love are very distinct from those
areas of the brain that are activated with sexual arousal (25) correlating
nicely with Dr. Fisher’s three divisions of love, namely, LUST, ROMANTIC LOVE
and LONG TERM ATTACHMENT. Bartels and Zeki conclude
their paper in poetic prose most unusual in scientific papers:
By showing that a unique set of
interconnected areas become active when humans view the face of someone who
elicits a unique and characteristic set of emotions, we have shown that
underlying one of the richest experiences of mankind is a functionally
specialized system of the brain. It is
perhaps surprising that so complex and overwhelming a sentiment should
correlate differentially with activity in such restricted regions of the brain…
(26)
Further functional MRI studies collaborating their findings have been done by Drs. Fisher,
Brown and Aron.
They also showed that the caudate nucleus was highly active when those
in love viewed the pictures of their lovers. In the words of Dr. Fisher:
…our most important finding was activity in
the caudate nucleus…the more passionate…the more active (the) caudate.(27)
Along with activity in the
caudate nucleus, Fisher’s research found high activity in another area of the
brain rich in dopamine producing cells called the ventral tegmental
area or VTA for
short. (Figure 2) (28). The most important point is that the
areas of the brain most active in ROMANTIC LOVE are the dopamine centers. However, since the caudate nucleus is so
active in lovers, Fisher refers to it as “the furnace of romantic love.” (29)
III. LONG TERM ATTACHMENT PHASE
Finally, gentlemen, a few brief comments
about the third phase of love called LONG TERM ATTACHMENT. Does it also have an
imbalance of chemicals at play and are there specific areas of the brain
activated with it? The answer to both is
“yes.” Recent research has shown that two neurohormones,
oxytocin and vasopressin, are elevated
in those who have been bonded in love for many years. Oxytocin is
released in women during childbirth and lactation and research has shown that
this chemical helps the mother to bond emotionally to her newborn. And
vasopressin has also been shown to be critical in long term bonding in rodents
and primates. (30) During intercourse,
these chemicals are released in both genders with breast and genital
stimulation as well as with orgasm. (31)
Oxytocin has also been shown to be released even when humans
hold hands or “snuggle,” resulting in its referral in the lay press as the
“cuddle hormone”. In short, with each
erotic moment with one’s beloved, nature is bonding the couple tighter and
tighter by elevating the oxytocin and vasopressin
levels. Wanderlust, by contrast, is
suppressed because testosterone levels are driven down when oxytocin
and vasopressin levels rise. (32)
The study by Bartels and Zeki that I mentioned earlier,
showed that the longer the lovers were in love, other parts of the brain, in
addition to the caudate nucleus, become active (namely the anterior cingulate gyrus and the insular
cortex). And in an additional study in
2003, they found that a particular type of long term attachment kind of love,
namely maternal love, activated areas of the brain that are rich in receptors
for oxytocin and vasopressin (periaqueductal
central gray matter or PAG). (33)
CONCLUSION
In conclusion, it seems that current
scientific research on the physiology of romantic love shows that the very
primitive areas of the brain correlated with reward and pleasure, are the same
as those activated when we are smitten with love. And, indeed gentlemen, does this not make
sense? If we as a species are to
continue, we need very primitive drives and rewards to make this happen. Propagation of the species is more than just
about sex. As very special mammals, our
young are helpless and need to be nurtured and protected for several years.
This nurturing and protective environment is best accomplished by a tightly
bonded male and female pair. And,
gentlemen, the bond that cements the couple tightly is romantic love and its
glue is, primarily, dopamine.
Sadly, however, that high energy,
besotted, and giddy phase of romantic love…that “divine madness”, as Plato
called it, seems to last, at most 2 to 4 years.
During that time frame, the chemicals of love, PEA, norepinephrine
and dopamine are at high levels. Those
chemicals in turn elevate testosterone driving the besotted couple to mate.
This time frame is long enough, however, for the couple in love to produce a
child and rear the child to at least the toddler stage at which point its
survival is less precarious and less dependent on constant parental
attention. Yet, if the oxytocin and vasopressin levels are increased enough during
the romantic love phase, long term attachment will develop and the couple with
remain together to continue to rear the child.
Well, as you can see gentlemen, the
present physiological understanding of romantic love has definitely been
enhanced by the new medical technology.
Commenting on the functional MRI studies by the Fisher team, Dr. Hans Breiter, director of Massachusetts General Hospital’s
Motivation and Emotion Neuroscience Collaboration, stated, “I distrust about 95% of the M.R.I.
literature and I would give this study an ‘A’; it really moves the ball in
terms of understanding infatuation love.” (34)
I must emphasize, however, that the information that I have shared with
you tonight, surely will not be the final word.
To quote Bartels and Zeki, “There is no doubt
that future studies will address these points more explicitly.” (35) However, I believe a case can be made that,
as it stands today, Plato and Hippocrates were correct: Love is a human
drive or a need reflected by an imbalance of chemicals in the body.
But, gentlemen, tonight, when you return
to your lover, and if she asks you, “Why do you love me?” what will you say? Will you say, “Darling, it is because when I
first looked at you, you raised my testosterone, PEA, dopamine and norepinephrine levels in my brain and with every touch my oxytocin levels increased so much that I cannot stand to
live my life without you.” I think
not. I think that you, as I, will always
turn to our artists for the perfect words.
When asked, “why do I love you?” I shall reply tonight….. because “you are my
north, my south, my east and my west.”(36)…. because “you make me smile with my
heart”(37)…. because “Night and day you are the one,
only you beneath the moon and under the sun.”….(38) because “It’s delightful, it’s delicious,
it’s de-lovely.” (39)
TYPES OF LOVE
Lust |
Romantic
Love |
Long
Term Attachment |
||||
^
Testosterone |
^Phenylethylamine |
^Vasopressin |
||||
^
Dopamine |
^Oxytocin |
|||||
^
Norepinephrine |
||||||
v
Serotonin |
||||||
^Libido |
^Obsessive
thoughts |
^Bonding |
||||
^Energy |
^Tenderness |
|||||
v
Appetite |
||||||
Lust
(Refs #1&2) |
FUNCTIONAL
MRI STUDIES Romantic
Love (Refs #3&4) |
Long
Term Attachment (Refs #5) |
||||
Sub
Cortical Regions Left
Caudate Nucleus Right
globus pallidus |
Sub
Cortical Regions Caudate
Nucleus Ventral
Tegmental Area Putamen |
Sub
Cortical Regions
Periaqueductal Central Gray
Matter (PAG) |
||||
Cortical
Regions Right
Insula (Deactivations
noted in Posterior Cingulate Cortex and Right
Hemisphere) |
Cortical
Regions Anterior
Cingulate Cortex
Left Middle Insula |
Cortical
Regions Lateral
orbito-frontal cortex |
REFERENCES TO THE
FUNCTIONAL MRI DATA
1. Stoleru, S, et al. Arch Sex Behav 28, 1-21 (1999).
2. Rauch SL, et al. Psychiatry Res 91, 1-10 (1999).
3. Bartels A, Zeki S. NeuroReport 11 #17 3829-3824 (2000)
4. Fisher, H. Why We Love: The Nature and Chemistry of Romantic Love. New York. Henry Holt and Company. 2004.
5. Bartels A, Zeki S. NeuroImage 21, 1156-1166 (2004).
ENDNOTES
1. Hamilton, Edith and Cairns, Huntington. 1961. Plato: The Collected Dialogues. Princeton University Press. P. 492.
2. Ibid., p.492.
3. Ibid., p. 496.
4. Ibid., p. 555.
5. Tallis PhD, Frank. 2004. Love Sick, Love as a Mental Illness. New York: Avalon Publishing Group Inc. p. 10.
6. Chandler, Robert. 1998. Sappho. London: Everyman’s Paperbacks. p. 10.
7. Tallis PhD, Frank. Ibid., p. 2.
8. Ibid., p. 12.
9. Ibid., p. 13.
10. Ibid., p. 13.
11. Ibid,. p. 13.
12. Ibid., p. 16.
13. Dickey, Franklin M. 1957. Not Wisely but Too Well: Shakespeare’s Love Tragedies. San Marino: Huntington Library. P. 30.
14. Loudon, Irvine. 1997. Western Medicine: An Illustrated History. Oxford: Oxford University Press. Pgs..78-79.
15. Tallis PhD, Frank. Ibid. P32.
16. Ibid., p. 36.
17. Ibid., p. 39.
18. Fisher, Helen. 2004. Why We Love: The Nature and Chemistry of Romantic Love. New York: Henry Holt and Company. Pgs 81-82.
19. Crenshaw. Theresa L. 1997. The Alchemy of Love and Lust: How our Sex Hormones Influence Our Relationships. New York: Simon and Shuster. P. 55-62.
20. Crenshaw, Theresa. Ibid. P. 134.
21. Fisher, Helen. Ibid. P. 83.
22. Crenshaw, Theresa. Ibid. P. 134.
23. Fisher, Helen. Ibid. P 53.
24. Bartels, A. and S. Zeki. The neural basis of romantic love. Neuroreport. (2000) 11#17:3829-3834. p. 3833.
25. Ibid. p. 3833.
26. Ibid, p. 3833.
27. Fisher, Helen. Ibid. P. 69.
28. Ibid., p. 71.
29. Ibid., p. 72.
30. Bartels, A. and S. Zeki. The neural correlates of maternal and romantic love. NeuroImage (2004) 21. P. 1155.
31. Fisher, Helen. Ibid., p. 89.
32. Ibid., p. 90.
33. Bartels, A. and S. Zeki. Ibid. P. 1156-1166.
34. Carey, Benedict. “Watching New Love as It Sears the Brain”. New York Times. May 31, 2005.