Romantic love: a mammalian brain
system for mate choice
Helen E. Fisher
, Arthur Aron
and Lucy L. Brown
Depar tment of Anthropology, Rutgers University, 131 George Street, New Brunswick,
NJ 08901-1414, USA
Depar tment of Psychology, State University of New York, Stony Brook, NY 11794, USA
Depar tment of Neuroscience, Department of Neurology, Albert Einstein College of Medicine,
New Haven, CT 06519-130, USA
Mammals and birds regularly express mate preferences and make mate choices. Data on mate choice
among mammals suggest that this behavioural ‘attraction system’ is associated with dopaminergic
reward pathways in the brain. It has been proposed that intense romantic love, a human cross-
cultural universal, is a developed form of this attraction system. To begin to determine the neural
mechanisms associated with romantic attraction in humans, we used functional magnetic resonance
imaging (fMRI) to study 17 people who were intensely ‘in love’. Activation speciﬁc to the beloved
occurred in the brainstem right ventral tegmental area and right postero-dorsal body of the caudate
nucleus. These and other results suggest that dopaminergic reward and motivation pathways
contribute to aspects of romantic love. We also used fMRI to study 15 men and women who had just
been rejected in love. Preliminary analysis showed activity speciﬁc to the beloved in related regions of
the reward system associated with monetary gambling for uncertain large gains and losses, and in
regions of the lateral orbitofrontal cortex associated with theory of mind, obsessive/compulsive
behaviours and controlling anger. These data contribute to our view that romantic love is one of the
three primary brain systems that evolved in avian and mammalian species to direct reproduction. The
sex drive evolved to motivate individuals to seek a range of mating partners; attraction evolved to
motivate individuals to prefer and pursue speciﬁc partners; and attachment evolved to motivate
individuals to remain together long enough to complete species-speciﬁc parenting duties. These three
behavioural repertoires appear to be based on brain systems that are largely distinct yet interrelated,
and they interact in speciﬁc ways to orchestrate reproduction, using both hormones and
monoamines. Romantic attraction in humans and its antecedent in other mammalian species play
a primary role: this neural mechanism motivates individuals to focus their courtship energy on
speciﬁc others, thereby conserving valuable time and metabolic energy, and facilitating mate choice.
Keywords: mate choice; romantic love; dopamine; oxytocin; vasopressin; evolution
1. ROMANTIC LOVE: A MAMMALIAN BRAIN
SYSTEM FOR MATE CHOICE
Individuals of many species exhibit mate preferences
and focus their courtship energy on these favoured
conspeciﬁcs. The phenomenon of ‘courtship attrac-
tion’ is so common in nature that the ethological
literature regularly uses several terms to describe it,
including ‘female choice’, ‘mate preference’, ‘individ-
ual preference’, ‘favouritism’, ‘sexual choice’ and
‘selective proceptivity’ (Andersson 1994). Charles
Darwin regarded this phenomenon, what has become
known as ‘mate choice’, as a central aspect of
intersexual selection, the type of sexual selection by
which individuals of one sex evolve traits that attract
members of the opposite sex (Darwin 1871/n.d).
Mammalian and avian species (as well as other
species) have evolved many physical and behavioural
characteristics by means of mate choice. The peacock’s
tail feathers are the standard example. But investi-
gations have focused on the traits that ‘display
producers’ have evolved to attract mates. The corre-
sponding neural mechanism by which ‘display choo-
sers’ become attracted to these traits and focus their
mating energy on particular preferred individuals,
thereby making a mate choice, has not been deﬁned.
Therefore, it has been proposed (Miller 2000; Fisher
et al. 2002a,b) that two aspects of intersexual selection
evolved in tandem: (i) traits that evolved in the ‘display
producer’ to attract mates, and (ii) corresponding
neural mechanisms in the ‘display chooser’, the
viewer of the display, that evolved to enable him/her
to discriminate between various displays, become
attracted to some and pursue these speciﬁc preferred
Several brain systems most probably operate in
tandem to orchestrate mate choice, including the
neural systems for sensory perception, memory, and
cognitive and emotional responses. But the speciﬁc
brain mechanism discussed in this review is the neural
mechanism that motivates the display chooser to pursue
a preferred mating partner, the courtship attraction
Phil. Trans. R. Soc. B (2006) 361, 2173–2186
Published online 13 November 2006
One contribution of 14 to a Theme Issue ‘The neurobiology of social
recognition, attraction and bonding’.
* Author for correspondence (helenﬁsher@helenﬁsher.com).
2173 This journal is q 2006 The Royal Society
system. Courtship attraction is characterized in
mammals by increased energy, focused attention,
obsessive following, afﬁliative gestures, possessive
mate guarding and motivation to win a preferred
mating partner (Fisher 2004).
A number of groups have reported that the basic
human motivations and emotions arise from distinct
systems of neural activity and that these brain systems
derive from mammalian precursors (Davidson 1994;
Panksepp 1998). Thus, it is parsimonious to suggest
that a mammalian brain mechanism for courtship
attraction is also active in Homo sapiens. Moreover,
because human romantic love (also known as passio-
nate love, obsessive love and ‘being in love’) is a
universal human phenomenon ( Jankowiak & Fischer
1992), because romantic love’s central characteristic is
mate preference and because ‘being in love’ exhibits
many of the other traits associated with mammalian
courtship attraction, it has been hypothesized that
human romantic love is a developed form of this
mammalian neural mechanism for mate choice (Fisher
1998). In most species, courtship attraction is brief,
lasting only for minutes, hours, days or weeks; in
humans, intense early stage romantic love can last
12–18 months (Marazziti et al. 1999) or more.
This review discusses the present evidence for this
brain system in mammals and humans, focusing on
recent neuroimaging studies of romantic love in
humans (Bartels & Zeki 2000, 2004; Aron et al.
2005; Fisher et al. 2005a,b). It examines how this
brain system varies from the sex drive and how it
changes across time (Aron et al. 2005). It also discusses
preliminary data on neural mechanisms associated with
romantic rejection (Fisher et al. 2005a,b). Finally, it
proposes that this brain system is one of the three
primary mating drives which interact in many ways and
which have evolved in mammalian and avian species to
direct various aspects of reproduction. (i) The sex drive
evolved to motivate individuals to seek copulation with
a range of partners, (ii) courtship attraction/romantic
love evolved to enable ‘display choosers’ to focus their
mating energy on speciﬁc mates, thereby conserving
courtship time and metabolic energy, and (iii) partner
attachment evolved to motivate mating individuals to
remain together long enough to perform species-
speciﬁc parental duties (Fisher 1998).
2. MAMMALIAN COURTSHIP ATTRACTION
‘It was evidently a case of love at ﬁrst sight, for she swam
about the new-comer caressingly...with overtures of
affection’ (Darwin 1871/n.d.). Darwin was describing a
female Mallard duck. Blackbirds, thrush, black grouse,
pheasants, these and many other birds, were reported as
‘fell in love with one another’ (Darwin 1871/n.d.).
A myriad of other descriptions of courtship attrac-
tion have been reported by ethologists (Andersson
1994). Gladikas (1995) reports of a free-ranging
orangutan living in the Tanjung Putting Reserve,
Borneo, ‘The object of TP’s adoration was Priscilla
. I thought that TP would have chosen a more comely
female. But . TP was smitten with her . He couldn’t
take his eyes off her. He didn’t even bother to eat, so
enthralled was he by her balding charms’. Housing
conditions are likely to alter the display of mate
preferences among laboratory animals when not
presented with a choice, but free-ranging individuals
regularly exhibit sexual favouritism.
Yet despite hundreds of ethological descriptions of
courtship attraction in a wide array of mammalian and
avian species, ethologists have traditionally lumped this
motivation/emotion system together with the sex drive.
However, there are exceptions. Beach (1976) made a
distinction between the sex drive and the courtship
attraction, writing that the occurrence of copulation
depended as much on individual afﬁnities and aver-
sions as upon the presence or absence of sex hormones
and that proceptive and receptive behaviour in the
female may depend upon different anatomical and
neurochemical systems in the brain. Hutchison &
Hutchison (1983) proposed that courtship entailed a
sequence of choices, each requiring different
mechanisms, and they questioned whether the sex
hormones had any speciﬁc role in the establishment
and expression of mating preferences. Pfaff (2002)
distinguishes between the hormone-dependent facili-
tation of sexual arousal and the expression of approach
and other courtship behaviours, regarding these as
distinct aspects of mating behaviour and physiology.
Kendrick & Dixson (1986) have shown that ante-
romedial hypothalamic lesions block proceptivity but
not receptivity in the female common marmoset.
Finally, Goodall (1986) reported that males of many
primate species ‘show clear-cut preferences for particu-
lar females, which may be independent of cycle stage’.
Various neurochemical mechanisms have also been
associated with courtship attraction. Darwin
hypothesized that female mate preferences arose from
their innate sense of beauty. But he (understandably)
offered no hypothesis regarding which speciﬁc neural
mechanisms might be involved (Darwin 1871/n.d.).
Miller (2000) noted that several faculties must have
evolved to discern and respond to the courtship traits of
display producers, referring to this constellation of
neural mechanisms as ‘mental machinery’ and ‘sexual
choice equipment’. Miller (2000) also distinguished
between ‘cold choosers’, such as insects that become
attracted to ornamental displays without any sensation
of pleasure, and ‘hot choosers’, animals whose choice
of mates is directed by subjective feelings of pleasure;
and he proposed that the endorphins may be involved
in the mate choices of hot choosers. Beach (1976)
suggested that the monoamines were involved in mate
preference, saying, ‘The mating behaviour of female
rats treated with monoamine receptor blocking agents
indicates that lordotic behaviour and soliciting
behaviour may be mediated by anatomically and
possibly neurochemically distinct systems’.
Present research supports Beach’s hypothesis. When
a female laboratory-maintained prairie vole (Microtus
ochrogaster) is mated with a male, she forms a distinct
preference for him associated with a 50% increase in
dopamine in the nucleus accumbens (Gingrich et al.
2000). When a dopamine antagonist is injected into the
accumbens, the female no longer prefers this partner
and when a female is injected with a dopamine agonist,
she begins to prefer the conspeciﬁc that is present at the
time of infusion, even if she has not mated with this
2174 H. E. Fisher and others Romantic love
Phil. Trans. R. Soc. B (2006)
male (Wang et al. 1999; Gingrich et al. 2000). An
increase in central dopamine is also associated with
courtship attraction in female sheep (Fabre-Nys 1997,
1998). In male rats, too, increased striatal dopamine
release has been shown in response to the presence of a
receptive female rat (Robinson et al. 2002; Montague
et al. 2004).
Recent data on several peptides also suggest that
central dopamine plays a role in regulating mate
preference. Kendrick & Dixson (1985) showed that in
marmosets, luteinizing hormone-releasing hormone
speciﬁcally facilitated female proceptive behaviours,
and oxytocin and vasopressin have been shown to
facilitate social recognition in mammalian species.
All of these peptides facilitate monoamine release
(Kendrick 2000). Therefore, it has been suggested
that mate preference may be inﬂuenced as these
peptides rewire brain circuits so that sensory and
other stimuli from speciﬁc individuals have more
potent effects on monoamine release, particularly
release of dopamine in brain reward centres (Lim
et al. 2004).
The extensive ethological literature on sexually
dimorphic traits that evolved to attract mates, in
conjunction with the above physiological data on
mate preference in several species, suggests that
intersexual selection involves interactions between the
display traits of display producers and a brain system
for mate preference in display choosers, courtship
attraction. Moreover, the data suggest that the brain
system for courtship attraction is distinct from, yet
operates in tandem with, the sex drive to orchestrate
proceptivity in birds and mammals. Finally, the
dopaminergic reward pathways may be involved.
3. HUMAN ROMAN TIC LOVE
It was appropriate to investigate this brain system in
Homo sapiens for several reasons. Foremost, intense
romantic love is a cross-cultural universal. In a survey
of 166 societies, Jankowiak & Fischer (1992) found
evidence of romantic love in 147 of them. No negative
data were found; in the 19 remaining cultures,
anthropologists had failed to ask the appropriate
questions; all were cases of ethnographic oversight.
Jankowiak & Fischer (1992) concluded that romantic
love constitutes a ‘human universal . or near universal’.
Moreover, romantic love is associated with a speciﬁc
set of physiological, psychological and behavioural
traits (Tennov 1979; Hatﬁeld & Sprecher 1986; Shaver
et al. 1987; Hatﬁeld et al. 1988; Harris & Christenfeld
1996; Fisher 1998; Gonzaga et al. 2001); and most of
these traits are also characteristic of mammalian
courtship attraction, including increased energy, focused
attention, obsessive following, afﬁliative gestures,
possessive mate guarding, goal-oriented behaviours
and motivation to win a preferred mating partner
(Fisher et al. 2002a,b; Fisher 2004).
Romantic love begins as an individual starts to
regard another individual as special and unique. The
lover then focuses his/her attention on the beloved,
aggrandizing the beloved’s worthy traits and over-
looking or minimizing his/her ﬂaws. The lover
expresses increased energy, ecstasy when the love affair
is going well and mood swings into despair during times
of adversity. Adversity and barriers heighten romantic
passion, what has been referred to as ‘frustration
attraction’ (Fisher 2004). The lover suffers ‘separation
anxiety’ when apart from the beloved and a host of
sympathetic nervous system reactions when with the
beloved, including sweating and a pounding heart.
Lovers are emotionally dependent; they change their
priorities and daily habits to remain in contact with
and/or impress the beloved. Smitten humans also
exhibit empathy for the beloved; many are willing to
sacriﬁce, even die for this ‘special’ other. The lover
expresses sexual desire for the beloved, as well as
intense sexual possessiveness, mate guarding. Yet the
lover’s craving for emotional union supersedes his/her
craving for sexual union with the beloved. Most
characteristic, the lover thinks obsessively about the
beloved, ‘intrusive thinking’. Rejected lovers ﬁrst
experience a phase of protest, during which they try
to win back the beloved and often feel abandonment
rage; then they move into the second stage of rejection,
associated with resignation and despair. Romantic love
is also involuntary, difﬁcult to control and generally
Since romantic love shares many characteristics
with mammalian courtship attraction, it has been
hypothesized that this human preference system
would also be associated with the monoamines,
speciﬁcally elevated activity of central dopamine
and/or central norepinephrine (Liebowitz 1983; Fisher
4. ROMANTIC LOVE: FUNCTIONAL MAGNETIC
RESONANCE IMAGING RESEARCH
To investigate the constellation of neural correlates
associated with romantic love, Fisher, Aron, Brown and
colleagues recruited 10 women and 7 men who were
intensely in love. The age range was 18–26 years
(MZ20.6; medianZ21); the reported duration of ‘being
in love’ was 1–17 months (MZ7.4; medianZ7). Each
participant was orally interviewed in a semi-structured
format to establish the duration, intensity and range of
his/her feelings of romantic love. Each also completed
the Passionate Love Scale (PLS), a 9-point Likert scale
self-report questionnaire which measures traits com-
monly associated with romantic love (Hatﬁeld &
Sprecher 1986; Cronbach’s alpha for questionnaire
reliability in this studyZ0.81; Cronbach 1951).
A preliminary investigation had identiﬁed a photo-
graph of the beloved as an effective stimulus for eliciting
feelings of intense romantic love (Mashek et al. 2000).
Thus, the protocol employed photographs and con-
sisted of four tasks presented in an alternating block
design: for 30 s, each participant viewed a photo of his/
her beloved (positive stimulus); for the following 40 s,
each performed a countback distraction task; for the
following 30 s, each viewed a photograph of an
emotionally neutral acquaintance (neutral stimulus);
and for the following 20 s, each performed a similar
countback task. The countback task involved viewing a
large number, such as 8421, and mentally counting
backwards (beginning with this number) in increments
of seven. We included the countback task to decrease
Romantic love H. E. Fisher and others 2175
Phil. Trans. R. Soc. B (2006)
the carry-over effect after the participant viewed the
positive stimulus because it is difﬁcult to quell intense
feelings of romantic love. This four-part sequence (or a
counterbalanced version beginning with the neutral
stimulus) was repeated six times; the total stimulus
protocol was 720 s (12 min). Pre-scanning instructions
were to think about a non-sexual euphoric experience
with the beloved; post-scanning interviews established
that the participants had engaged in romantic thinking
Group activation speciﬁc to the beloved occurred in
several regions, including the right ventral tegmental
area (VTA) localized in the region of A10 dopamine
cells (Aron et al. 2005). The VTA is a central region of
the brain’s reward system (Wise 1996; Schultz 2000;
Martin-Soelch et al. 2001), associated with pleasure,
general arousal, focused attention and motivation to
pursue and acquire rewards (Schultz 2000; Delgado
et al. 2000; Elliot et al. 2003).
The VTA sends projections to several brain
regions (Gerfen et al . 1987; Oades & Halliday 1987;
Williams & Goldman-Rakic 1998), including the
caudate nucleus where we also found group activations,
speciﬁcally in the right medial and postero-dorsal body
(Aron et al. 2005). The caudate plays a role in reward
detection and expectation, the representation of goals
and the integration of sensory inputs to prepare for
action (e.g. Schultz 2000; Martin-Soelch et al. 2001;
Lauwereyns et al. 2002; O’Doherty et al. 2002). Zald
et al. (2004) found that predictable monetary reward
presentation caused dopamine release in the medial
caudate body where we found activation.
Using functional magnetic resonance imaging
(fMRI), Bartels & Zeki (2000) also investigated brain
activity in 17 men and women who reported being
‘truly, deeply and madly in love’. Eleven were women;
all looked at a photograph of his/her beloved, as well as
photographs of three friends of similar age, sex and
length of friendship. But the participants in that study
had been in love substantially longer than those in our
study (28.8 months versus 7.4 months tZ4.28,
p!0.001). They were also less intensely in love. This
was established because both study groups were
(serendipitously) administered the same questionnaire
on romantic love, the PLS (respective scores were 7.55
versus 8.54, tZ3.91, p!0.001). In spite of these
differences in protocol, Bartels & Zeki (2000, 2004)
found activity in regions of the ventral tegmental area
and caudate nucleus, as we did.
These data are consistent with the above animal
literature, suggesting that mesolimbic dopamine
pathways in the reward system of the brain play a role
in the pleasurable feelings, focused attention,
motivation and goal-oriented behaviours associated
with romantic love. However, activation of subcortical
dopaminergic pathways of the VTA and caudate
nucleus may comprise only the ‘general arousal’
component (Pfaff 1999) of this brain system for mate
preference and mate pursuit (Fisher 2004).
Other neurotransmitters are likely to be involved,
including glutamate in the mesocortical system, owing
to their role in the release of dopamine in the VTA
(Legault & Wise 1999) and/or their fast signals in the
prefrontal cortex regarding reward (Lavin et al. 2005).
Central norepinephrine may also be associated with
courtship attraction (Fisher 1998). This was
hypothesized because increased activity of nor-
epinephrine generally produces alertness, energy,
sleeplessness and loss of appetite (Coull 1998; Robbins
et al. 1998), increased attention (Posner & Peterson
1990) and increased memory for new stimuli (Grifﬁn &
Taylor 1995), some of the primary characteristics of
human romantic love (Tennov 1979; Hatﬁeld &
Sprecher 1986; Fisher 2004). As norepinephrine is
also associated with peripheral sympathetic nervous
system responses, including increased heart rate,
sweating and trembling, central norepinephrine may
contribute to these aspects of romantic love/courtship
attraction as well (Fisher 1998).
The above data suggest that mammalian courtship
attraction and human romantic love are associated with
dopaminergic reward pathways in the brain. These data
also support the hypothesis that romantic love is
distinct from the sex drive (Aron & Aron 1991; Fisher
5. THE SEX DRIVE
The sex drive is characterized by the urge for sexual
gratiﬁcation. It is associated with the androgens and
oestrogens in non-primate mammalian species and
primarily with the androgens in many primates,
especially humans (Edwards & Booth 1994; Sherwin
1994; Van Goozen et al. 1997). Humans with higher
circulating levels of testosterone tend to engage in more
sexual activity (Edwards & Booth 1994; Sherwin
1994). Women tend to feel more sexual desire during
increases (Van Goozen et al. 1997). Both sexes have
fewer sexual fantasies, masturbate less regularly and
engage in less intercourse as levels of the androgens
decline with age (Edwards & Booth 1994).
The balance between the androgens, oestrogens and
other bodily systems, as well as childhood and adult
experiences and a host of other biological and
environmental factors play a role in when, where and
how often individuals express the sex drive (Nyborg
1994). Nevertheless, the androgens are central to the
sex drive and these gonadal and adrenal hormones have
not been associated with human romantic love. More-
over, when humans self-administer androgens to boost
sex drive, they do not report that they fall in love. These
two neural systems do not always act in tandem in
Several fMRI studies support the hypothesis that the
sex drive is associated with speciﬁc networks of brain
activation and that these networks are largely distinct
from those associated with human romantic love/
mammalian courtship attraction. Arnow et al. (2002)
reports that when young male heterosexual subjects
look at erotic video material while wearing a custom-
built pneumatic pressure cuff around the penis, their
sexual arousal is associated with strong activations in
the right subinsular region, including the claustrum,
left caudate and putamen, right middle occipital/
middle temporal gyri, bilateral cingulate gyrus, right
sensorimotor and pre-motor regions, and right
2176 H. E. Fisher and others Romantic love
Phil. Trans. R. Soc. B (2006)
Using fMRI, Beauregard et al. (2001) measured
brain activation in men as they viewed erotic ﬁlm
excerpts. Activations occurred in limbic and paralimbic
structures, including the right amygdala, right
anterior temporal pole and hypothalamus. Using
fMRI, Karama et al. (2002) also recorded brain activity
while men and women viewed erotic ﬁlm excerpts.
Activity increased in the anterior cingulate, medial
prefrontal cortex, orbitofrontal cortex, insula and
occipitotemporal cortices, as well as in the amygdala
and ventral striatum. Men showed activation in the
thalamus and signiﬁcantly greater activation than
women in the hypothalamus, speciﬁcally in a sexually
dimorphic area associated with sexual arousal and
behaviour. Animal studies also indicate that several
brain structures are associated with the sex drive and
sexual expression, including the medial amygdala,
medial preoptic area, paraventricular nucleus and
periaqueductal gray (PAG; Heaton 2000), as well as
the septum and the ventromedial hypothalamus
Although the neural regions associated with the sex
drive overlap those associated with courtship attrac-
tion, these two neural systems show many differences,
suggesting that the primary brain system for the sex
drive is distinct from the brain system associated with
human romantic love (Aron & Aron 1991; Fisher
1998). Anecdotal behavioural data in humans support
this hypothesis. (i) The sex drive is focused on a speciﬁc
goal, sexual union with another, and romantic love is
focused on a different goal, emotional union with
another. (ii) The sex drive is often expressed towards a
range of individuals and romantic love is focused on one
particular individual. (iii) The sex drive is often
temporarily quelled when satisﬁed and romantic love
does not decrease with coitus and often persists
unabated for months, even years. (iv) Most liberated
adults have engaged in coitus with individuals for
whom they felt no romantic love and many have also
been ‘in love’ with someone with whom they have had
no physical contact.
Several lines of investigation indicate that the sex
drive and the courtship attraction/romantic love are
distinct neural systems, designed to orchestrate
different aspects of the reproductive process. The sex
drive enables individuals to initiate courtship and
mating with a range of partners; courtship attraction/
romantic love motivates them to focus their mating
energy on speciﬁc individuals, thereby conserving time
and metabolic energy.
Nevertheless, the brain systems for the sex drive and
the courtship attraction regularly interact to coordinate
mammalian mate choice.
6. THE SEX DRIVE AND MATE PREFERENCE:
The biological relationships between the sex drive and
the courtship attraction are most likely dose dependent
and variable, depending on which brain regions are
involved and many other biological and environmental
factors. However, data suggest that these brain systems
have a positive correlation.
Animal studies indicate that elevated activity of
dopaminergic pathways can stimulate a cascade of
reactions, including the release of testosterone and
oestrogen (Wenkstern et al. 1993; Kawashima &Takagi
1994; Ferrari & Giuliana 1995; Hull et al. 1995, 1997,
2002; Szezypka et al. 1998; Wersinger & Rissman
2000). Likewise, increasing levels of testosterone and
oestrogen promote dopamine release (Hull et al. 1999;
Auger et al. 2001; Becker et al. 2001; Appararundaram
et al. 2002; Creutz & Kritzer 2002; Pfaff 2005). When a
male rat is placed in an adjacent cage, where he can see
or smell an oestrous female, activity of central
dopamine increases and contributes to sexual arousal
and pursuit of the female (West et al. 1992; Wenkstern
et al. 1993; Hull et al . 1995, 1997, 2002). When the
barrier is removed and the male is allowed to copulate,
activity of dopamine continues to rise in the medial
preoptic area (Hull et al. 1995). When dopamine is
injected into speciﬁc brain regions of the male rat, the
infusion stimulates copulatory behaviour (Ferrari &
Giuliana 1995). Blocking the activities of central
dopamine in rats diminishes several proceptive sexual
behaviours, including hopping and darting (Herbert
1996). Finally, electrochemical studies in male rats
show increased dopamine release in the dorsal and the
ventral striatum in response to the presence of a
receptive female rat (Robinson et al. 2002; Montague
et al. 2004). Pfaff (2005) reports that in male rats,
dopamine increases male sexual behaviour in at least
three ways: it increases sexual arousal and courtship
behaviour; it potentiates the motor acts of mounting;
and it facilitates genital responses to stimulation.
This positive relationship between elevated activity
of central dopamine, elevated sex steroids and elevated
sexual arousal and sexual performance (Herbert 1996;
Fiorino et al. 1997; Liu et al. 1998; Pfaff 2005) also
occurs in humans (Walker et al. 1993; Clayton et al.
2000; Heaton 2000). When individuals exhibiting
hypoactive sexual desire disorder are treated with
dopamine-enhancing medications, libido improves
(Segraves et al. 2001). When patients suffering from
depression take drugs that elevate central dopamine
activity, their sex drive often improves (Walker et al.
1993; Ascher et al. 1995; Coleman et al. 1999). In fact,
since elevated activity of central serotonin is inhibitory
to the sex drive (Rosen et al. 1999; Montejo et al. 2001),
some patients taking serotonin-enhancing antidepress-
ants supplement this therapy with medications that
elevate the activity of dopamine (and norepinephrine)
solely to maintain or elevate sexual appetite and arousal
(Walker et al. 1993; Ascher et al. 1995; Coleman et al.
1999; Rosen et al. 1999).
Animal studies indicate that norepinephrine is also
positively linked with sexual motivation and sexual
arousal (Van Bockstaele et al. 1989; Clayton et al. 2002;
Fraley 2002; Pfaff 2005). When a female prairie vole is
exposed to a drop of male urine on the upper lip,
norepinephrine in the olfactory bulb contributes to the
release of oestrogen and concomitant proceptive
behaviour (Dluzen et al.1981). The reverse also
occurs; oestradiol and progesterone contribute to the
release of norepinephrine in the hypothalamus to
produce lordosis in rats (Etgen et al. 1999). Moreover,
when ovariectomized, sexually receptive female rats
Romantic love H. E. Fisher and others 2177
Phil. Trans. R. Soc. B (2006)
receive injections of oestrogen and are then permitted
to mate, copulation produces the release of nor-
epinephrine in the lateral ventromedial hypothalamus
(Etgen & Morales 2002). Drug users attest to this
positive chemical relationship between norepinephrine
and the sex drive. In the right oral dose, amphetamines
(norepinephrine and dopamine agonists) enhance
sexual desire (Buffum et al. 1988).
The complex interaction between these catechol-
amines and gonadal hormones suggests why the sex
drive and the courtship attraction have traditionally
been lumped into a single behavioural category,
proceptivity. Instead, these distinct neural systems
appear to work in tandem to enable display choosers
to explore an array of mating partners, focus their
courtship attention on preferred individuals and then
sustain attraction and sexual arousal long enough to
complete species-speciﬁc mating behaviours.
7. PARTNER ATTACHMENT
The full array of brain systems associated with court-
ship, mating and parenting and the interactions
between these brain systems need further investigation
(Fisher & Thomson in press). Nevertheless, the
available literature suggests that at least three distinct,
yet interrelated neural systems play a role in reproduc-
tion: the sex drive, courtship attraction and partner
attachment. Each of these motivation/emotion systems
is associated with a different behavioural repertoire,
each is associated with a different and dynamic
constellation of neural correlates and each evolved to
direct a different aspect of reproduction (Fisher 1998).
The relationship between courtship attraction/roman-
tic love and the sex drive has been discussed above, and
partner attachment is considered next.
Partner attachment, or pairbonding, in birds and
mammals is characterized by mutual territory defence
and/or nest building, mutual feeding and grooming,
maintenance of close proximity, separation anxiety,
shared parental chores and afﬁliative behaviours. The
ethological literature commonly infers that this con-
stellation of attachment behaviours associated with
pairbonding evolved primarily to motivate mating
partners to sustain an afﬁliative connection long
enough to complete species-speciﬁc parental duties.
This parental attachment system has been associated
with the activity of the neuropeptides, oxytocin (OT) in
the nucleus accumbens and arginine vasopressin (AVP)
in the ventral pallidum (Carter 1992; Winslow et al.
1993; Wang et al. 1994; Carter et al. 1997; Yo u n g et al.
1998; Lim & Young 2004; Lim et al. 2004), although
the brain’s opioid system (Moles et al. 2004) and other
neural systems are involved as well (Kendrick 2000).
Bowlby (1969, 1973) and Ainsworth et al. (1978)
proposed that, to promote survival of the young,
primates have evolved an innate attachment system
designed to motivate infants to seek comfort and safety
from their primary caregiver, generally their mother.
More recently, researchers have emphasized that this
attachment system remains active throughout their life
and serves as a foundation for attachment between
spouses as they raise children (Hazan & Shaver 1987;
Hazan & Diamond 2000). Data from the Demographic
Yearbooks of the United Nations on 97 societies
suggest the prevalence of this attachment system in
humans. Approximately 93.1% of women and 91.8%
of men marry by age 49 (Fisher 1992). Pairbonding
and attachment behaviours are central aspects of the
multi-part human reproductive strategy (Fisher 1992).
Hatﬁeld (1988) refers to feelings of attachment as
companionate love, which she deﬁnes as ‘a feeling of
happy togetherness with someone whose life has
become deeply entwined with yours’. Extensive
research has been done on this attachment system in
adults (Fraley & Shaver 2000), but this literature does
not regularly distinguish between feelings of attach-
ment and feelings of romantic love (Aron et al. 2006).
However, cross-cultural and historical data indicate
that people in other societies and centuries do
distinguish between feelings of romantic love and
Nisa, a !Kung Bushman woman of the Kalahari
Desert, Botswana, reported, ‘When two people are ﬁrst
together, their hearts are on ﬁre and their passion is
very great. After a while, the ﬁre cools and that’s how it
stays. They continue to love each other, but it’s in a
different way–-warm and dependable’ (Shostak 1981).
The Taita of Kenya say that love comes in two forms, an
irresistible longing, a ‘kind of sickness’, and a deep
enduring affection for another (Bell 1995). In Korea,
‘sarang’ is a word close to the western concept of
romantic love, while ‘chong’ is more like feelings of
long-term attachment; Abigail Adams, wife of Amer-
ica’s second president, distinguished these feelings
when writing to John Adams in 1793, ‘Years subdue
the ardor of passion, but in lieu thereof friendship and
affection deep-rooted subsists, which deﬁes the ravages
of time’ (McCullough 2001).
Current brain imaging investigations in humans and
animal studies indicate some of the neural correlates of
this attachment mechanism. These data also suggest
that the neural correlates for attachment are distinct
from those for early-stage intense romantic love in
humans and courtship attraction in other mammalian
species, yet these two brain systems interact.
8. NEUROIMAGING AND ANIMAL STUDIES
As discussed earlier, using fMRI, Bartels & Zeki
(2000) studied 17 men and women who were in love.
However, their subjects were in love for an average of
28.8 months, a considerably longer period of time
compared with our participants who were in love for
an average of 7.4 months (Aron et al. 2005); their
subjects were less passionately in love (Aron et al.
2005). Their participants also exhibited activity in
several brain regions where our subjects showed none,
including the anterior cingulate cortex and mid-
These varying results stimulated us to examine the
subset of our subjects in longer relationships, speci-
ﬁcally those who were in love between 8 and 17
months. In our subset of individuals in longer
relationships, several regions showed activations,
including the right anterior and posterior cingulate
cortex, and right mid-insular cortex (Aron et al. 2005).
2178 H. E. Fisher and others Romantic love
Phil. Trans. R. Soc. B (2006)
Thus, we conﬁrmed Bartels & Zeki’s (2000) ﬁndings
that the anterior cingulate and insular cortex are
involved in longer term love relationships.
More relevant to this discussion, we also found
activation in the ventral putamen/pallidum (Aron et al.
2005). Activity in this region, associated with a speciﬁc
distribution pattern of vasopressin (V1a) receptors, has
been linked with pairbonding and attachment
behaviours in monogamous prairie voles (Lim &
Young 2004; Lim et al. 2004), monogamous California
mice and monogamous marmosets, whereas promiscu-
ous white-footed mice and promiscuous rhesus mon-
keys do not express pairbonding/attachment
behaviours or this distribution of V1a receptors in the
ventral pallidum (Wan g et al. 1997; Young et al. 1997;
Bester-Meredith et al. 1999; Young 1999). Hence,
activity in the ventral pallidum is greater in longer term
human relationships than in shorter ones and activity in
the ventral pallidum, speciﬁcally associated with
vasopressin, is evident in other pairbonding/attaching
But vasopressin activity in the ventral pallidum also
affects partner preference, a central characteristic of
mammalian courtship attraction and human romantic
love. Lim & Young (2004) report that arginine
vasopressin antagonists infused into the ventral palli-
dum prevented partner preference formation among
male prairie voles. Yet they also report that V1aR
activation in this region is necessary for pairbond
formation (Lim & Young 2004).
Activity of central oxytocin in the nucleus accum-
bens also contributes to both pairbonding and partner
preference (Lim et al. 2004). Williams et al. (1994)
report that when oxytocin was administered intracer-
ebroventricularly, ovariectomized female prairie voles
preferred the partner who was present at the time of
infusion; and Lim, Murphy and Young report that
when an oxytocin receptor (OTR) antagonist is infused
directly into the nucleus accumbens of a female prairie
vole, this antagonist blocks partner preference forma-
tion (Yo u n g et al. 2001; Lim et al. 2004). Yet they also
conclude that among monogamous prairie voles, OTRs
and vasopressin V1a receptors (V1aR) in the ventral
forebrain play critical roles in the formation of
Research on the genetic basis of pairbonding also
lumps partner preference and attachment behaviours.
Pitkow et al (2001) reported that structural differences
in the V1 receptor gene of socially monogamous male
voles (as opposed to asocial promiscuous voles)
increased levels of the expression of this receptor in
the ventral pallidum; moreover, these males also
exhibited heightened levels of social afﬁliation. They
formed a preference for a speciﬁc female and began to
cohabit with her, even though they had not mated with
this female. Lim, Young and colleagues report that
when they transfected this genetic variant (the monog-
amous version) into the pallidum of meadow voles, an
asocial promiscuous species, vasopressin receptors
were upregulated; each male also began to ﬁxate on a
par ticular female and mate exclusively with her, even
though other females were available (Lim et al. 2004).
The activities of central oxytocin and vasopressin
have been associated with both partner preference and
attachment behaviours, while dopaminergic pathways
have been associated more speciﬁcally with partner
preference. So Lim et al. (2004) integrate these data,
proposing that when monogamous prairie voles and
other pairbonding creatures engage in sex, copulation
triggers the activity of vasopressin in the ventral
pallidum and oxytocin in the nucleus accumbens and
facilitates dopamine release in these reward regions,
which motivates males and females to prefer a current
mating partner and initiates attachment/pairbonding
behaviours. Moreover, males of promiscuous species
(who lack one link in this chain for encoding the V1a
receptor for vasopressin in the ventral pallidum) most
probably feel attraction, but do not associate this
pleasurable feeling with their speciﬁc mating partner so
they do not initiate a longer term attachment. In
species that do not form these bonds, this relationship
with dopamine reward centres is much weaker
Like the brain systems for the sex drive and the
courtship attraction, the neural mechanism for
attachment is complex, ﬂexible, varies in its threshold
and intensity and is most likely integrated with many
other brain systems (Kendrick 2000), probably
including the opioids (Moles et al. 2004). Never-
theless, the above data suggest that the neural systems
for courtship attraction and partner attachment work
in tandem in a pairbonding species, motivating
individuals to prefer a speciﬁc mating partner and
also motivating them to form an attachment to this
mate. These data also suggest that courtship attrac-
tion and partner attachment can operate indepen-
dently in non-monogamous species, enabling
individuals to prefer speciﬁc mating partners yet
avoid long-term attachments.
Data on the neural correlates of maternal love
support the proposition that feelings of attachment
and feelings of romantic love are distinct yet inter-
related neural systems. Bartels & Zeki (2004) used
fMRI to measure brain activity in mothers while each
looked at a photo of her own infant, an infant with
whom she was acquainted, an adult best friend and an
adult acquaintance. They then compared these data on
the neural mechanisms associated with maternal
attachment with their data on the neural correlates of
(later stage) romantic love (Bartels & Zeki 2000).
Maternal love activated several speciﬁc brain regions
that differed from those associated with romantic love,
including the lateral orbitofrontal cortex and the PAG.
Maternal love also activated some brain regions that
were the same as those activated by romantic love,
including regions of the medial insula, anterior
cingulate gyrus and caudate nucleus. Finally, activity
associated with maternal love and romantic love
overlapped in brain areas rich in oxytocin and
vasopressin receptors, including the substantia nigra
(Bartels & Zeki 2004).
The neural ﬂexibility of these brain systems for
reproduction and their interactions with one another
and other brain systems are complex (Kendrick 2000).
For example, central dopamine (and norepinephrine)
can stimulate the release of oxytocin and vasopressin in
neurohypophyseal tissues (Kendrick et al.1992;
Ginsberg et al. 1994; Galﬁ et al. 2001); but increasing
Romantic love H. E. Fisher and others 2179
Phil. Trans. R. Soc. B (2006)
activity of central dopamine can also inhibit release of
central oxytocin (Seybold et al. 1978; Vizi & Volbekas
1980). Increasing activity of central oxytocin can
stimulate release of norepinephrine and dopamine
(Kendrick 2000) or interfere with dopamine and
norepinephrine pathways (Schwarzberg et al. 1981;
Kovacs & Telegdy 1983; Kovacs et al. 1990; Van de Kar
et al. 1998). Finally, a small microsatellite repeat
sequence in the gene coding for V1aR controls its
density of expression in the ventral pallidum and this
gene region is subject to a number of polymorphisms
that contribute to variability in the strength of mono-
gamous bonding in male prairie voles (Hammock &
Young 2005). The Homo sapiens version of this gene
has similar polymorphisms, which might contribute
to individual differences in human monogamous
pairbonding as well.
The above data suggest that the mammalian
attachment system is distinct from, yet interacts with,
the neural mechanisms for courtship attraction and the
sex drive. This ﬂexible, combinatorial system would
provide individuals of myriad species with the range of
motivations, emotions and behaviours necessary to
pursue their species-speciﬁc reproductive strategy.
These data on attachment and romantic love also
lend perspective to another aspect of reproduction,
rejection in love.
9. REJECTION IN LOVE
Romantic love is expressed in many graded forms, but
it has two extremes: love that is returned and love that is
rejected. To understand the range of neural
mechanisms associated with mate choice, Fisher,
Aron, Brown and colleagues used fMRI to study 10
women and 5 men who were still very much in love but
had recently been rejected by their romantic partner
(Fisher et al. 2005a,b). We used the same protocol as
with our happily in-love subjects (Aron et al. 2005).
Rejected participants alternately viewed a photograph
of their abandoning beloved (positive stimulus) and a
photograph of a familiar, emotionally neutral individ-
ual (neutral stimulus), interspersed with a distraction–
Preliminary analysis of the positive–neutral contrast
showed signiﬁcant group effects in the right nucleus
accumbens/ventral putamen/pallidum, lateral orbito-
frontal cortex and anterior insular/operculum cortex
(Fisher et al. 2005a,b). We then compared these data on
rejected lovers with the results from our study of 17
happily in-love individuals (Aron et al. 2005). Rejected
lovers expressed signiﬁcantly greater activity in the
ventral striatum/putamen/pallidum than did those who
were happily in love (ﬁgure 1).
Other studies have shown that the nucleus accum-
bens/ventral pallidum/putamen region where we found
activity becomes more active as an individual chooses a
high-risk investment associated with big gains or big
losses, making it an uncertain gain (Kuhnen &
Knutson 2005), or anticipates a money reward (Zald
et al. 2004); data from rat studies are consistent with
the idea that the nucleus accumbens core is important
for choices for uncertain rewards and delayed
reinforcement (e.g. Cardinal & Howes 2005); activity
in the nucleus accumbens has also been associated with
pairbond formation and maintenance in prairie voles
(Lim et al. 2004). The region of the anterior insula/
operculum cortex where we found activity has been
associated with skin and muscle pain and with anxiety
(Schreckenberger et al. 2005). The region of the lateral
orbitofrontal cortex where we found activity has been
associated with theory of mind (Vollm et al. 2006),
evaluating punishers (Kringelbach & Rolls 2004),
implementing appropriate adjustments in behaviour
(Ridderinkhof et al. 2004), obsessive/compulsive
behaviours (Evans et al. 2004) and with controlling
anger in recently abstinent cocaine-dependent individ-
uals (Goldstein et al. 2005).
These results suggest that brain systems associated
with reward and motivation remain active in recently
romantically rejected men and women, but differ in
their precise location. These preliminary results also
suggest that neural regions associated with risk-taking
for big gains or losses, physical pain, obsessive/com-
pulsive behaviours, ruminating on the intentions and
actions of the rejecter, evaluating options, and emotion
regulation increase in their activity when someone is
rejected by a beloved.
Our study is the second investigation of romantic
rejection. Najib et al. (2004) studied nine women who
were ‘actively grieving’ over a recent romantic break-
up. Our preliminary comparisons uncovered no
commonalities; in fact, in several regions where we
found activations, they found deactivations. Since our
subjects regularly reported anger and hope for reconci-
liation, while subjects in the Najib et al. (2004) study
more regularly reported acceptance, we suspect that
our subjects were in the initial stage of romantic
rejection, the protest phase, while their participants
were largely in the subsequent resignation/despair
The combined aforementioned data may contribute
understanding to the high cross-cultural rates of
stalking, homicide, suicide and clinical depression
associated with rejection in love (Meloy & Fisher
–10 –8 –6
Figure 1. Three axial sections through the human brain at
2 mm intervals show a consistent activation difference
between a group happily in love and a group in love but
recently rejected (yellow colour, p!0.01). Those who were
recently rejected show greater activation in the right ventral
putamen–pallidum and accumbens core (side deﬁnition is
radiological convention) than those who were happily in love.
These regions have been associated with reward, especially
uncertain large gains and losses in gambling, and uncertain
reinforcement in rats. (Figure data from Aron et al. 2005 and
a preliminary report, Fisher et al. 2005a,b).
2180 H. E. Fisher and others Romantic love
Phil. Trans. R. Soc. B (2006)
10. THE DRIVE TO LOVE
The psychological literature distinguishes between
emotions (affective states of feeling) and motivations
(brain systems oriented around the planning and
pursuit of a speciﬁc want or need). Aron has proposed
that romantic love is not primarily an emotion, but a
motivation system designed to enable suitors to build
and maintain an intimate relationship with a preferred
mating partner (Aron & Aron 1991; Aron et al. 1995).
The fMRI and animal experiments we have reviewed
above support Aron’s hypothesis. The VTA is directly
associated with motivation- and goal-oriented
behaviours, as is the caudate nucleus. Moreover, the
caudate nucleus has widespread afferents from all of the
cortex except primary visual areas (Kemp & Powell
1970; Selemon & Goldman-Rakic 1985; Saint-Cyr
et al. 1990; Eblen & Graybiel 1995; Flaherty &
Graybiel 1995) and is organized to integrate diverse
sensory, motor and limbic functions (Brown 1992;
Parthasarathy et al. 1992; Eblen & Graybiel 1995;
Parent & Hazrati 1995; Parent et al. 1995; Brown et al.
1998; Haber 2003). Thus, regions of the caudate
nucleus could effectively integrate the behavioural and
biological actions associated with a complex state, such
as romantic love.
In fact, these ﬁndings suggest that romantic love is
a primary motivation system, a fundamental human
mating drive (Fisher 2004). Pfaff (1999) deﬁnes a
drive as a neural state that energizes and directs
behaviour to acquire a particular biological need to
survive or reproduce and he reports that all drives are
associated with the activity of dopaminergic pathways
and a few other speciﬁc neural systems (as well as
other neural systems speciﬁc to each individual drive
state). Romantic love has many characteristics in
common with drives (Fisher 2004). (i) Like drives,
romantic love is tenacious and emotions ebb and ﬂow,
(ii) romantic love is focused on a speciﬁc reward and
emotions are associated with a range of phenomena
instead, (iii) romantic love is not associated with a
distinct facial expression and the primary emotions
are all associated with speciﬁc facial expressions,
(iv) romantic love is difﬁcult to control and all of the
basic drives are difﬁcult to control, and (v) human
romantic love and mammalian courtship attraction
are associated with dopamine-rich neural regions and
all the basic drives are also associated with dopamin-
ergic pathways. Drives lie along a continuum. Thirst
is almost impossible to control, while the sex drive
can be redirected, even quelled. Romantic love is
evidently stronger than the sex drive because when
one’s sexual overtures are rejected, people do not kill
themselves or someone else. Instead, abandoned
lovers sometimes stalk, commit suicide or homicide
or fall into a clinical depression.
More investigations need to be made to understand
the ﬂexibility, variability and durability of this neural
mechanism for mate choice, romantic love. Data could
be collected on how the neural mechanisms for
romantic love vary in conjunction with speciﬁc
traumatic childhood experiences; how speciﬁc person-
ality proﬁles affect the biological expression of romantic
love; how speciﬁc diseases, such as schizophrenia and
Parkinson’s disease, and addictions, such as cocaine,
amphetamine and alcohol addiction, facilitate or
inhibit the biological expression of romantic love;
how the constellation of neural correlates associated
with romantic love varies during the course of a long-
term relationship; how the biology of romantic love
varies according to sexual orientation; and how this
brain system varies in cultures with different marital
patterns and in different mammalian species with
diverse reproductive strategies. More research into
the brain mechanisms associated with romantic love
may also help to explain some of the basic principles of
brain lateralization and lend further understanding of
the reward system and its interactions with cognitive
and emotional processes that together produce
It might also be valuable to investigate gender
differences in the constellation of neural correlates
associated with early stage (and later stage) romantic
love. In a preliminary study of gender differences, we
did a between-subject analysis of our 10 women and 7
men who were happily in love. Although men and
women were similar in many ways, we did ﬁnd gender
differences. Men tended to show more activity than
women in a region of the right posterior dorsal insula
that has been correlated with penile turgidity (Arnow
et al. 2002) and male viewing of beautiful faces (Aharon
et al. 2001). Men also showed more activity in regions
associated with the integration of visual stimuli
(Narumoto et al. 2001). Women tended to show more
activity than men in regions associated with attention,
memory and emotion (Gray et al. 2002; Maddock et al.
2003; Velanova et al. 2003).
Extensive cross-cultural data indicate that courting
men respond more strongly than women to visual
signals of youth and beauty (Buss et al. 1990); hence,
we speculate that the above male activation pattern
evolved, in part, to enable ancestral men to respond to
the visual signals of women who could bear them viable
young (Fisher 2004). Cross-cultural data indicate that
women are more attracted than men to potential mates
who offer status and resources (Buss et al. 1990). To
calculate the reproductive value of a man, a woman
must remember the promises and provisioning record
of her potential partner. Thus, we speculate that the
above female activation pattern evolved, in part, to
enable ancestral women to remember male behaviour
patterns and thus make adaptive long-term mate
choices (Fisher 2004). But more research is necessary
to conﬁrm this hypothesis, to establish the cultural
variables that contribute to gender differences and to
ﬁnd more gender differences in the brain associated
with romantic love.
We expect that human romantic love will be found to
engage a wide range of varying, overlapping and
dynamic brain systems, as would be appropriate of a
multi-faceted phenomenon that has signiﬁcant social,
reproductive and genetic consequences. Nevertheless,
the primary neural correlates associated with intense,
early-stage romantic love are likely to remain similar
across individuals and cultures, even among species,
because this neural mechanism evolved to direct a
crucial aspect of mammalian reproduction, mate
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