The Neural Basis of Love as a Subliminal Prime: An Event-related Functional Magnetic Resonance Imaging Study
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The Neural Basis of Love as a Subliminal Prime:
An Event-related Functional Magnetic
Resonance Imaging Study
S. Ortigue1,2, F. Bianchi-Demicheli3, A. F. de C. Hamilton1,
and S. T. Grafton1,2
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Abstract
& Throughout the ages, love has been defined as a motivated not. Behavioral results showed that subliminal presentation of
and goal-directed mechanism with explicit and implicit mech- either a beloved’s name (love prime) or a passion descriptor
anisms. Recent evidence demonstrated that the explicit repre- (passion prime) enhanced reaction times in a similar fashion.
sentation of love recruits subcorticocortical pathways mediating Subliminal presentation of a friend’s name (friend prime) did
reward, emotion, and motivation systems. However, the neural not show any beneficial effects. Functional results showed that
basis of the implicit (unconscious) representation of love re- subliminal priming with a beloved’s name (as opposed to either
mains unknown. To assess this question, we combined event- a friend’s name or a passion descriptor) specifically recruited
related functional magnetic resonance imaging (fMRI) with a brain areas involved in abstract representations of others and
behavioral subliminal priming paradigm embedded in a lexical the self, in addition to motivation circuits shared with other
decision task. In this task, the name of either a beloved partner, sources of passion. More precisely, love primes recruited the
a neutral friend, or a passionate hobby was subliminally pre- fusiform and angular gyri. Our findings suggest that love, as a
sented before a target stimulus (word, nonword, or blank), and subliminal prime, involves a specific neural network that sur-
participants were required to decide if the target was a word or passes a dopaminergic–motivation system. &
INTRODUCTION
have been reported, such as euphoria, loss of appetite,
Love, one of the deepest forms of human endeavor, is hyperactivity, delay of the onset of fatigue, and a de-
defined as a complex state involving chemical, cogni- creased need for sleep (Aron et al., 2005; Buss, 2003;
tive and goal-directed behavioral components (Bianchi- Sternberg & Barnes, 1988; Hatfield & Walster, 1978). It
Demicheli, Grafton, & Ortigue, 2006; Aron et al., 2005; has also been shown that love has stress-reducing and
Fisher, Aron, & Brown, 2005; Bartels & Zeki, 2000, 2004; health-promoting potentials (Esch & Stefano, 2005).
Buss, 2003; Mashek, Aron, & Fisher, 2000; Sternberg Recently, two functional magnetic resonance imag-
& Barnes, 1988; Aron & Aron, 1986, 1996; Hatfield & ing (fMRI) studies reinforced the assumption that love
Walster, 1978). When involved in a passionate and inti- is a goal-directed state that leads to a range of emo-
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mate relationship, the person actively strives for the tions, rather than a specific emotion (Aron et al., 2005;
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happiness of the loved person (Clark & Mills, 1979). Bartels & Zeki, 2000). These studies showed that in-
Passionate love is often coupled with the inability to feel tense ongoing love, as compared to friendship, recruits
passion for more than one person at a time (Berscheid subcorticocortical pathways mediating reward, emotion,
& Meyers, 1996). In this sense, love has often been in- and motivation systems (Aron et al., 2005; Fisher et al.,
tertwined with passion and defined as a motivated, goal- 2005; Bartels & Zeki, 2000, 2004). More precisely, the
directed desire (Aron & Aron, 1996; Aron et al., 2005; blood oxygen level dependent signal (BOLD) specific to
Ovid, 1986). For instance, the old adage ‘‘Do what you explicit viewing of photographs of a loved partner
love and never have to work another day in your life’’ revealed activity focally restricted to the mid insula,
illustrates the motivation component of love. anterior cingulate cortex, head of the caudate nucleus,
As a goal-directed motivator, love has various behav- ventral tegmental area, putamen, bilateral posterior
ioral effects. For instance, different explicit effects of love hippocampus, left inferior frontal gyrus, left middle
temporal gyrus, and cerebellum (Aron et al., 2005;
Bartels & Zeki, 2000) as well as the right parietal lobe
1
Dartmouth College, 2University of California, Santa Barbara, (only in Aron et al., 2005). Critically, the central role of
3
Geneva University Hospital, Switzerland the dopaminergic–motivation system in ongoing love
D 2007 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 19:7, pp. 1218–1230has been emphasized by high positive correlations Fisher et al., 2005; Aron & Aron, 1986, 1996). However,
between the subjective feeling of love (passionate love a beloved’s name and a friend’s name do not vary ex-
scale [PLS] scores; Hatfield & Sprecher, 1986) and BOLD clusively on the motivation dimension. Many variables
responses recorded from the anteromedial caudate can induce differential brain activities between these
nucleus (Aron et al., 2005). Thus, there is now some two types of stimuli. One of these variables is the simple
explicit functional evidence supporting the hypothesis frequency with which someone thinks about their sig-
that love, as a motivator, is a powerful source of nificant other, as opposed to their friend. The amount
behavior via dopaminergic circuits (e.g., Berscheid & of time someone spends thinking about a beloved or a
Meyers, 1996; Sternberg & Barnes, 1988; Aron & Aron, friend or both may indeed play a crucial role on the
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1986, 1991). salience of each of these stimuli and thus lead to distinct
However, it is unknown if the implicit representation brain activities between these stimuli. In order to ex-
of love involves similar motivation/dopaminergic circuits. clude this confounding variable, we also included a novel
The previous two functional studies of the neural systems type of prime as a control for frequency of thoughts,
underlying love used only explicit tasks with faces (Aron that is, a descriptor for a passionate interest, tailored to
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et al., 2005; Bartels & Zeki, 2000) where explicit percep- each individual, that induced frequency of thoughts that
tion of familiar stimuli and conscious processing are were equivalent to the frequency of thoughts about a
potential confounds (due to top-down interference) for beloved. Thus, in the present study, each experimental
assessing selective unconscious mechanisms (Dehaene, trial was randomly preceded by the subliminal presenta-
Changeux, Naccache, Sackur, & Sergent, 2006; Dehaene tion of one out of three different types of visual stimuli
& Changeux, 2000; Dehaene, Kerszberg, & Changeux, (primes): the name of the participant’s beloved (love
1998). Thus, the true benefit of love and its neural net- prime), and two control primes, that is, a name of the
work on information processing without any top-down participant’s friend (friend prime), or the participant’s
conscious interference remains unknown. passion (passion prime).
Here, we specifically assessed this question by com- This design allowed us to test whether the neural basis
bining event-related fMRI and a behavioral lexical deci- of the unconscious mental representation of love de-
sion task embedded in a subliminal priming paradigm, pends on (a) motivational/emotional components (by
which is one of the more reliable ways of observing contrasting love primes vs. friend primes and passion
unconscious mechanisms if they exist. Subliminal prim- primes vs. friend primes), (b) salience of the stimuli (by
ing is indeed a powerful experimental manipulation that contrasting love primes vs. passion primes), or both. For
provides a unique opportunity to examine the mecha- instance, although we cannot exclude that passion for a
nisms of implicit cognition. Typically, in subliminal person is different from passion for sports, art, or objects,
priming, a brief presentation (approximately less than we assume that love primes and passion primes, as impli-
50 msec) of a masked visual stimulus induces a change cit motivators, might share some common neural mech-
(e.g., facilitation) in the speed or accuracy of the pro- anisms (as opposed to friend primes) that could affect
cessing of a following target stimulus (priming effect; cognition, as previously predicted (Bianchi-Demicheli
e.g., Bianchi-Demicheli et al., 2006; Henson, 2003; Musch et al., 2006). This neurofunctional assumption is coherent
& Klauer, 2003; Dehaene, Naccache, et al., 1998; Eimer with the recent Dehaene–Changeux computational
& Schlaghecken, 1998; Murphy & Zajonc, 1993; Fazio, model that suggests the reinforcement (via Hebbian-type
Sanbonmatsu, Powell, & Kardes, 1986). Facilitation ef- learning) of conceptual associations by reward-motivated
fects due to subliminal priming may occur not only learning mechanisms (Dehaene & Changeux, 2000;
when the relation between primes and targets is a Gisiger, Dehaene, & Changeux, 2000). According to this
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perceptual one, but also when it is a conceptual one model, the internal representation of a reward signal is
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(e.g., Spruyt, Hermans, De Houwer, & Eelen, 2004; coded in n cortical areas of contribution weighted by
Musch & Klauer, 2003; Dehaene, Naccache, et al., ‘‘synaptic efficacities’’ w0, w1, . . ., wn. Both reward and
1998). Love (as opposed to friendship) can be consid- expectation signals converge at the level of the ventral
ered as a goal-directed drive that may induce implicit tegmental area, and learning modifies synaptic weights to
facilitation effects on cognitive behavior due to motiva- minimize the discrepancies between the two. The output
tional and emotional mechanisms rather than a pure of this ventral tegmental area adequately reproduces
selective emotion without any motivational component dopamine release during performance of various tasks
(Bianchi-Demicheli et al., 2006; Aron et al., 2005). In (Gisiger et al., 2000). This Hebbian-based model illus-
light of this, one might expect our subliminal priming trates the principle of cognitive learning by production
paradigm used in combination with event-related fMRI and selection of pre-representation. Critically, because
to show that the unconscious processing of a beloved’s this model also posits that mental representations of
name (as opposed to a control friend’s name) facilitates stimuli may be distributed over different brain areas
the behavioral processing of a subsequent stimulus according to their conceptual structure (Pulvermuller,
through the recruitment of dopamine-rich brain re- 1996, 1999), one might expect that our three types of
gions (Bianchi-Demicheli et al., 2006; Aron et al., 2005; prime stimuli (love, friend, and passion) have overlapping
Ortigue et al. 1219and partly distinct neural representations on the basis of racy, or functional imaging data. Finally, participants
any differences in contextual encoding. were asked to provide the name of a male friend of
similar age, sex and duration of friendship as their part-
ners, with the imposed condition that they did not feel
METHODS any emotional, physical, or intellectual attraction for him,
such that this friend was neutral in the love dimension.
Participants The names of the participant’s beloved, passion, and
Thirty-six healthy heterosexual women, aged 20.1 ± 3.2 friend were used as primes during the fMRI scanning as
(mean ± SD) years who were dating, engaged, or detailed below.
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married to someone and who had a favorite passion in
life (e.g., science, sports, art) provided written informed
Procedure
consent to participate in this experiment, which was ap-
proved by the Committee for Protection of Human Sub- During the scanner session, participants were instructed
jects. Participants were recruited from the Dartmouth to perform a lexical decision task each time that they saw
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College experiment scheduling system on the basis of a visual stimulus flash onto the screen. They were asked
advertisements indicating that experimenters were seek- to indicate as rapidly and as accurately as possible whether
ing individuals who were currently intensively in love. All or not an English word was presented on that trial. Re-
participants had normal or corrected-to-normal vision, sponses were made by pressing one of two response but-
were not taking antidepressant medication, and had no tons on a keyboard with fingers of the right hand (‘‘yes’’
chemical dependency and psychiatric or neurological response with the index finger to words and ‘‘no’’ re-
illnesses. All participants were right-handed (Edinburgh sponse with the middle finger to nonwords or blanks).
Handedness Inventory, Oldfield, 1971). The visual stimulus on each trial was composed of
Just prior to the scanning session, one of us (S.O.) a sequence of three frames (Figure 1) following a stan-
interviewed each participant in a semistructured format dard subliminal priming paradigm. First, a prime word
to obtain general personal information (such as date of was presented for 26 msec, followed by a mask of
birth; handedness) and to establish the range of each ########## symbols for 150 msec and then the
participant’s feelings of passionate love. This semistruc- target word for 26 msec. Stimulus onset asynchrony
tured interview, based on standard studies, provided (SOA; i.e., the interval between the onset of the prime
insights into the women’s feelings about their beloved, and the onset of the target) was 176 msec. Trials were
the duration and the intensity of their love relationship, separated by an interstimulus interval randomly chosen
and the percentage of time they think about their be- between 1500 and 6000 msec to allow accurate model-
loved during their waking hours (Fisher, 2004; Hatfield ing of the hemodynamic response. All stimuli were
& Sprecher, 1986). Then, each participant completed presented using Cogent 2000 running in Matlab 7.0.1
one standard self-report questionnaire: the PLS (Hatfield under Windows XP, which provides control of display
& Sprecher, 1986; example items: ‘‘For me, (name of durations and accurate recordings of reaction times.
the beloved) is the perfect romantic partner’’; ‘‘I would Stimuli appeared in lowercase 43-point Courier New
rather be with (name of the beloved) than anyone else’’; font, in white on a black background.
‘‘I have an endless appetite for affection from (name Each trial was composed of one of three primes
of the beloved)’’. The reported duration of ‘‘being in together with one of 40 words, or one of 40 nonwords,
love’’ with their partner was 1–60 months (15.3 ± 14.5 or one of 40 ‘‘blank’’ trials, giving a total of 360 possible
[mean ± SD]). trials. Each of the possible trials was then randomly
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On average, participants had a PLS score of 7.7 ± 1.22 assigned to one of six blocks by means of a Latin square,
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(SD) out of 9 points. The participant’s subjective inten- which ensures that each block contained an equal
sity of love for their partner was 7.36 ± 1.85 (SD) on a number of beloved primes, passion primes, and friend
9-point scale. primes, and an equal number of words, nonwords, and
As part of the same interview, participants were also blanks; and words were never presented twice in a
asked about their passions in life, and every participant block. Trial order within a block was pseudorandomized
provided the name of a passionate hobby. As a selec- with the constraint of no more than three consecutive
tion criterion, only participants who reported think- trials with the same target type. Each participant per-
ing about their passion 60% of the day were included formed six blocks with 60 trials in each block, for a total
in the experiment. A t test conducted between percent of 360 trials, which took up to 40 min including breaks
of thoughts dedicated to the partner and percent of between each block.
thoughts dedicated to the passion did not reveal any
significant difference, t(35) = 0.299, p = .766. Because
Prime Stimuli
this selection criterion was used for all participants,
there was a ceiling effect of this variable. No correlation For each participant, three unique words (3 to 11
could have been done with reaction times (RTs), accu- characters long) were used as prime stimuli. The first
1220 Journal of Cognitive Neuroscience Volume 19, Number 7Figure 1. Experimental
design. Stimulus sequence.
The visual stimulus on each
trial was composed of a
sequence of three frames. First,
a prime word was presented
for 26 msec, followed by a
mask of ##########
symbols for 150 msec and then
the target word for 26 msec.
Subjects were not informed
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of the presence of the prime.
The type of target letter strings
(emotional words, nonwords,
or blanks) and the type of the
primes (beloved, e.g., Romeo;
neutral friend, e.g., Albert;
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and passion, e.g., piano) were
randomly presented according
to a Latin square calculated
over the six experimental
blocks. This means a target
stimulus was not presented
twice in the same block in
order to avoid any effects of
familiarization. In addition,
the order of experimental
trials was random, with the
constraint of no more than
three consecutive trials with
the same target type.
name (either full first name, such as Robert, or short- were selected to be high in written word frequency,
ened first name, such as Bob) of the participant’s and the other half were low in written word frequency
beloved was designated as the ‘‘love prime.’’ No nick- according to the Kucera and Francis linguistic database
name was used in the present study. A noun describing (Kucera & Francis, 1967). In addition, a 2 3 analysis of
the participant’s passion in life (e.g., dance, piano, variance (ANOVA) performed between low- versus high-
softball), as supplied by the participant, was designated frequency targets and the prime types did not show any
as the ‘‘passion prime,’’ and finally, the name of a friend main interaction: F(2,70) = .44, p = .65 for reaction
was designed as the ‘‘friend prime’’ or ‘‘control prime.’’ times; F(2,70) = .41, p = .96 for accuracy. All words
No difference in name length between love, friend, and were selected to be high in valence and high in arousal
passion primes was observed, F(2,70) = 2.69; p = .08. (Bradley & Lang, 1999). High- (M = 220.95, SD =
The presence of the prime was not mentioned to the 144.67) and low-frequency (M = 27.6, SD = 27.13)
subjects. To check that participants were not aware of emotional words were matched in word length (high-
the type of prime stimuli, we used an extensive debrief- frequency words: M = 5.9, SD = 1.48; low-frequency
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ing procedure in which participants were asked increas- words: M = 6.3, SD = 1.95; p = .48), valence (high-
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ingly specific questions about the study. This procedure frequency words: M = 7.40, SD = 0.64; low-frequency
revealed that all participants reported that they had seen words: M = 7.55, SD = 0.66; p = .57), arousal (high-
the flash of the mask. However, no participant could frequency words: M = 5.89, SD = 0.44; low-frequency
report on the specific emotional or semantic contents of words: M = 6.42, SD = 1.17; p = .054), abstractness
the flashes. (high-frequency words: M = 407,38, SD = 123,64; low-
frequency words: M = 404.6, SD = 118.84; p = .95;
Coltheart, 1981).
Target Stimuli
The 80 target letter-string stimuli (3 to 11 characters
Magnetic Resonance Imaging
long) included 40 positive emotional English nouns and
a set of 40 pronounceable nonwords (following the Imaging was performed with a 3T Phillips MRI scanner
same consonant/vowel structure as words). Emotional using an eight-channel phased-array head coil. For each
words were selected from the Affective Norms for functional run, an echo planar gradient-echo imaging
English Words (Bradley & Lang, 1999). In order to con- sequence sensitive to BOLD contrast was used to ac-
trol any effect of word frequency, one half of the words quire 30 slices per repetition time (TR) (4 mm thickness,
Ortigue et al. 12210.5 mm gap), with a TR of 1976 msec, echo time (TE) of that used a recruitment method similar to ours, we first
35 msec, flip angle of 908, field of view (FOV) of 240 mm, calculated correlations between the various scores we
and 80 80 matrix. One hundred fifty-seven whole- obtained. We tested whether the questionnaire data cor-
brain images were collected in each run. After all the related significantly with relationship length or percent
functional runs, a high-resolution T1-weighted image of of thoughts (or whether any of these variables corre-
the whole brain was acquired using a spoiled gradient lated with each other); they did not (Table 1). That is,
recalled 3-D sequence (TR = 9.9 msec; TE = 4.6 msec; as was found by Aron et al. (2005), there were no sig-
flip angle = 88, FOV = 240 mm; slice thickness = 1 mm, nificant correlations among PLS scores and length of
matrix = 256 256). being in love (Pearson correlation, r = .15, p = .39).
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Because in the present study, scores obtained at the
PLS, 9-point scale, and the percent of daily thoughts
Functional Image Processing
dedicated to the beloved were highly correlated with
All analysis was carried out in SPM2 (www.fil.ion.ucl.ac. each other (Table 1), we calculated a composite mea-
uk/spm). First, functional images were realigned to cor- sure by combining the individual measures of these
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rect for head movement. Then, data were coregistered three scales (averaged as Z scores). There was no cor-
to the SPM2 EPI template, and normalized to a stan- relation between this composite measure and length
dardized Montreal Neurological Institute (MNI) stereo- of being in love (Pearson correlation, r = .15, p = .38;
taxic space to give images with 2 2 2-mm voxels. Table 1).
A design matrix was fitted for each subject with the Our behavioral results showed that both the sublimin-
trials in each cell of the three-by-three factorial de- al presentation of passion (580 ± 19.58 msec [mean ±
sign (3 primes 3 target types) modeled by a standard SE]) and love (581 ± 19.92 msec [mean ± SE]) induced
hemodynamic response function and its temporal de- beneficial effects (faster reaction times) on the explicit
rivative. Each trial was modeled as a single event with detection of words, love: F(1,35) = 5.22; p = .03; pas-
zero duration, starting at the onset of the prime stimu- sion: F(1,35) = 6.74; p = .01, compared to the sub-
lus. Rest was not modeled. The design matrix weighted liminal presentation of a control friend’s name (607 ±
each raw image according to its overall variability to re- 23.4 msec [mean ± SE]). No behavioral difference was
duce the impact of movement artifacts (Diedrichsen & found between love and passion ( p = .95). No specific
Shadmehr, 2005). The design matrix was fit to the data beneficial effect of prime was found for nonword detec-
for each participant individually. After estimation, betas tion, F(2,70) = 0.15; p = .87. However, a general main
were smoothed (10-mm full width half maximum) and effect of prime was found independently of the target,
taken to the second level for random effect analysis. F(2,70) = 4.09; p = .02, indicating that subjects were
faster to respond after a beloved prime (608 ± 19.49
[mean ± SE]) or a passion prime (607 ± 19 [mean ±
Second level Data Analysis
Our analysis aimed to identify which brain areas within
the standard ‘‘prime network’’ were preferentially acti- Table 1. Pearson’s r Correlation Coefficient between Each
vated by love and passion regardless of the target type. Measure of Love (PLS, 9-Point Scale, and Percent of Thoughts)
To this purpose, we first identified the brain regions in- and Length of Duration
volved in the primed lexical decision task. This contrast of
Pearson’s r 9-Point
all primes > rest was thresholded at p < .001 uncorrected
Correlation Intensity Percent of Length of
and used to generate an inclusive mask of the priming
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Coefficient PLS Scale Thoughts Duration Composite
network in the brain. Within this mask, we calculated con-
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trasts for love > friend, passion > friend, love > passion, PLS 1 S*** S*** ns –
and passion > love, and report results that passed a 9-Point .86 1 S*** ns (trend) –
threshold of p < .01 and a cluster size of 10 voxels. We intensity
used a masking approach to restrict the likelihood of scale
false positives rather than a region-of-interest approach,
Percent of .73*** .61*** 1 ns –
because the lack of previous studies of subliminal prim- thoughts
ing for love and passion means that we cannot make
strong a priori predictions of the locations of our results. Length of .15 .33 .02 1 .15
duration
Composite – – – 1
RESULTS Composite averages the individual measures of the three love scales
Behavioral Results (as Z scores), that is, PLS, 9-point intensity scale, and percent of
thoughts. PLS = passionate love scale; S = significant; ns = non-
In order to compare our results with two previous significant, p > .05; trend = trend of significance, .05 < p < .06.
fMRI studies (Aron et al., 2005; Bartels & Zeki, 2000) ***p < .001.
1222 Journal of Cognitive Neuroscience Volume 19, Number 7SE]) than after a friend prime (621 ± 21.41 [mean ± friend’s name. There was also no specific beneficial effect
SE]). A 2 3 ANOVA involving simple effects of primes of prime on target nonword detection, F(2,70) = 0.06;
(love, friend, passion) and letter-string types (words, p = .94, or target blank detection, F(2,70) = 0.49, p = .61.
nonwords) revealed a trend of significant interaction, No general main effect of prime was found indepen-
F(2,70) = 2.83, p = .06, suggesting that participants tend dently of the target, F(2,70) = 0.31; p = .73.
to be faster in detecting target words (and not non-
words). This effect occurred especially if the target
Functional Imaging Results
words were primed by love/passion (as opposed to
friendship). An overall 3 3 ANOVA did not show any First, our functional results showed that the subliminal
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interaction between the different types of targets presentation of a beloved’s name (as opposed to a
(words, nonwords, blanks) and the different types of friend’s name) recruited a cerebral network that is partly
primes (love, friend, passion), F(4,140) = 1.79; p = .13, concordant with the cerebral network previously found
mainly due to absence of main effect of primes for a for the explicit presentation of love-related stimuli (Aron
blank target, F(2,70) = 0.28, p = .75. et al., 2005; Bartels & Zeki, 2000). More precisely, in
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A trend of negative correlation was observed between comparison with a control stimulus (love > friend con-
PLS scores and reaction times (the more participants trast), the subliminal presentation of a beloved’s name
were in love, the faster they were) for target stimuli recruited the caudate nucleus, ventral tegmental area,
primed by a beloved’s name (Pearson correlation, r = insula, bilateral fusiform regions, parahippocampal gyri,
.29, p = .04). A similar trend of correlation was found angular gyrus, left dorsolateral middle frontal gyrus, left
between PLS scores and reaction times to passion inferior temporal gyrus, occipital cortex, and cerebel-
primes (Pearson correlation, r = .29, p = .04). No lum (Table 2). The two previous studies (Aron et al.,
similar correlation was found between PLS scores and 2005; Bartels & Zeki, 2000) that investigated the expli-
reaction times to friend primes (Pearson correlation, r = cit mechanisms of love using a similar contrast showed
.25, p = .07). A test evaluating the significance of brain area activation restricted to the mid insula, ante-
differences between these two correlation coefficients rior cingulate cortex, head of the caudate nucleus,
(r = .25 and r = .29) was nonsignificant ( p = .86). ventral tegmental area, putamen, bilateral posterior hip-
In addition, a negative correlation was found between pocampus, left inferior frontal gyrus, left middle tem-
the percentage of daily thoughts for the partner and poral gyrus, and cerebellum as well as the right parietal
reaction times (the more participants thought about lobe (only in Aron et al., 2005).
their beloved every day, the faster they were) for target On the other hand, our study demonstrated that the
stimuli primed by a beloved’s name (Pearson correla- subliminal presentation of another motivator, such as a
tion, r = .40, p = .008). A similar negative correlation passion’s descriptor (as compared to a friend’s name,
was also found between percentage of thoughts for the i.e., passion > friend contrast), showed greater activa-
beloved and reaction times to passion primes (Pearson tion in the caudate nucleus, insula, bilateral fusiform
correlation, r = .38, p = .01) as well as with reaction regions, parahippocampal gyri, right angular gyrus, oc-
times to friend primes (Pearson correlation, r = .29, cipital cortex, lingual gyrus, and cerebellum (Table 2).
p = .04). A test evaluating the significance of differences Taken together, our functional results thus showed
between the two correlation coefficients related to love potentially overlapping brain activation between love
and passion primes (r = .40 and r = .38) or between (love > friend contrast) and passion primes (passion >
love/passion and friend primes was nonsignificant (love friend contrast). Both love primes (love > friend con-
vs. passion: p = .92; love vs. friend: p = .61; passion vs. trast) and passion primes (passion > friend contrast) led
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friend: p = .68). to increases in BOLD signal in regions within motivation
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No significant correlation was observed between and emotion systems, compared with a control friend
length of love relationship and reaction times (Pearson prime ( p < .01; Table 2). Specifically, both love and pas-
correlation, for beloved primes: r = .21, p = .11; for sion primes activated the caudate nucleus, insula, bi-
friend primes: r = .20, p = .12; for passion primes: r = lateral fusiform regions, parahippocampal gyrus, right
.24, p = .08). angular gyrus, occipital cortex, and cerebellum.
No significant effects were observed for accuracy. An Finally, when we directly compared BOLD responses
overall 3 3 ANOVA did not show any interaction obtained from love and passion primes ( p < .01; Fig-
between the different types of targets and primes, ure 2; Table 2), we found some differences of brain acti-
F(4,140) = .78, p = .54. A 2 3 ANOVA involving simple vation. Love primes (as opposed to passion primes, love
effects of primes (love, friend, passion) and letter-string > passion contrast) revealed significant activation in bi-
types (words, nonwords) did not reveal any significant lateral angular gyri (Table 1; in orange in Figure 2A and
interaction, F(2,70) = 0.037, p = .96. There was no B); and bilateral fusiform regions (Table 2; in orange in
main effect of love, F(1,35) = 0.93, p = .34, or passion, Figure 2C and D).
F(1,35) = 0.68, p = .41, on the detection of target words, On the other hand, passion primes (as opposed to
compared to the subliminal presentation of neutral love primes, passion > love contrast) showed significant
Ortigue et al. 1223Table 2. MNI Coordinates of Cerebral Activation Peaks
Coordinates Love > Friend Passion > Friend Love > Passion Passion > Love
Regions x y z t t Cluster Size t Cluster Size t Cluster Size t Cluster Size
Thalamus 6 8 10 6.14
Caudate nucleus 6 12 0 5.34 4.39 80 3.49 193
Brainstem/midbrain 6 22 22 4.90 3.21 13
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Insula 26 20 4 4.97 3.75 2275 3.47 7
36 4 2 3.73 3.72 291 3.01 193
Occipitotemporal/ 36 88 18 5.33 2.38 49 2.58 17
fusiform region
48 50 24 4.65 3.33 57 2.62 17 3.11 148
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64 52 16 4.25 2.47 21 2.66 113
56 70 2 3.47 3.18 52
Parahippocampal gyrus 34 18 28 5.03 4.06 405 2.71 21
40 8 34 4.91 2.79 46 3.15 100 3.30 191
Angular gyrus 64 50 22 4.35 2.65 51
66 44 32 4.33 2.45 27 2.62 46 2.43 68
Dorsolateral middle 46 26 26 4.51 3.09 112
frontal gyrus
52 38 22 3.78
Superior temporal gyrus 66 14 8 4.18
Inferior temporal gyrus 44 26 20 4.39 2.70 43 2.40 21
64 22 10 4.52
Occipital cortex 18 96 8 6.00 2.51 138 2.61 42
18 94 8 5.22 3.72 744
Precuneus 16 76 20 4.32
Lingual gyrus 12 68 2 4.05 2.41 52
Cingulate gyrus 10 40 20 3.97
6 42 8 3.25 3.21 19
Precentral gyrus 64 2 24 3.66 2.96 160
Cerebellum 12 48 38 5.17 2.76 142 3.48 518
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36 78 52 4.04 4.3 651 4.45 510 2.63 184
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activation in the bilateral temporo-occipital junction, with activation in two of the regions that were signifi-
left parahippocampal and inferior temporal gyrus, left cant for the contrast by itself, the right anteromedial
cingulate gyrus, right precentral gyrus, and cerebellum caudate body (r = .60, p = .012) and the septum–fornix
(Table 2; in blue in Figure 2). region (r = .54, p = .008). That is, the Aron et al. study
In order to specifically compare our results with those participants who self-reported higher levels of love than
obtained previously by Aron et al. (2005), we performed others also showed greater activation than others in
a between-subjects random effect analysis correlating this region of the caudate and septum when viewing
BOLD responses and participant’s scores on the PLS their beloved (Aron et al., 2005). (For planned compari-
scores, first focusing on the love > friend contrast, as sons, Aron et al. applied small volume corrections with
the Aron et al. analysis did. This method used previously a sphere as a region of interest. The coordinates for the
by Aron et al. is known to provide strong evidence for centers of the following regions of interest were re-
the link of a function with an activated area. In the Aron ported: VTA, caudate nucleus, putamen, accumbens/
et al. study, PLS scores had high positive correlations subcallosal cortex/ventral striatum, amygdala, posterior
1224 Journal of Cognitive Neuroscience Volume 19, Number 7Figure 2. BOLD responses
obtained for love compared
to passion (love > passion
in orange; passion > love in
blue), shown on lateral views
of the fiducial left and right
side of the brain. BOLD time
courses, averaged over prime
type (red, love; blue, passion;
yellow, friend) were extracted
for the significant regions
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between love and passion
(love > passion) contrasts
and are shown for the angular
gyrus (A, left; B, right) and
fusiform gyrus (C, left; D,
right). Brain activities were
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mapped using the PALS human
cortical atlas from Caret5
software (Van Essen, 2005).
hippocampus, cingulate, insula, retrosplenial cortex, and Focusing on the love > passion contrast (as described
medial and lateral orbitofrontal cortex). As we did for in Table 2), we found the same method of analysis
our previous analyses described above, we performed showed high positive correlations between PLS scores
this focused ‘‘love > friend contrast’’ between-subjects and three of the cerebral regions that were significant
random effect analysis within the prime network (as de- for the contrast by itself, the left angular gyrus (Pearson
scribed in Table 2). We corrected our correlations for correlation, r = .50; p = .002; Figure 3, Table 3) and the
multiple comparisons and only allowed a significant fusiform region bilaterally (left: r = .46; p = .005; right:
threshold at p < .01. Our results showed similar and r = .47; p = .003; Table 3). That is, participants who self-
also distinct findings as compared to the findings of Aron reported higher levels of love than others also exhibited
et al. Focusing on the love > friend contrast, our find- greater activation than others in these brain regions.
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ings showed that PLS scores had high positive corre- Because no studies have investigated the love > passion
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lations with activation in some of the cerebral regions contrast previously, we also performed additional ana-
that were significant for the contrast by itself, that is, lyses correlating BOLD responses and the different love
the caudate nucleus (r = .48, p = .003), right para- measures (9-point subjective intensity scale, percent of
hippocampal gyrus (Pearson correlation, r = .46, p = thoughts, length of being in love). This approach offers
.005), angular gyrus (r = .39, p = .01), insula (left: r = a broad overview of the present findings, although they
.41, p = .01; right: r = .38, p = .02), ventral tegmental were highly correlated with each other (as shown in
area (r = .38, p = .02), and the left dorsolateral mid- Table 1). The 9-point subjective intensity scale had simi-
dle frontal gyrus (r = .40, p = .01). That is, participants larly correlated with the same brain regions: the left
who self-reported higher levels of love than others ex- angular gyrus (r = .43, p = .009) and the fusiform region
hibited greater activation than others in these brain bilaterally (left: r = .46, p = .005; right: r = .44, p = .007;
regions. Table 3). On the other hand, percent of thoughts only
A similar method of analysis applied for the passion > showed a positive correlation with the right fusiform
friend contrast (as reported in Table 2) did not reveal region (r = .43, p = .008) and a trend to a positive cor-
similar significant correlation between BOLD responses relation with the left angular gyrus (r = .396, p = .017;
and participant’s scores on the PLS scores. Table 3). No correlation was observed between the
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Figure 3. Brain activation correlated with the passionate love scale (PLS) scores of participants ( p < .01 corrected). (Left) Angular gyrus
location for the correlation. (Right) Correlation of activity in the left angular gyrus with PLS scores. Participants who scored higher on the PLS
scale showed stronger activations in a specific site ( 60, 52, 28; x, y, z [mm] MNI coordinates) of a larger part of the angular gyrus.
length of time in love and the regions that were signif- Love as an Implicit Motivator
icantly activated for this specific contrast.
First, we aimed to test whether facilitation priming
effects could occur for unconscious representation of a
beloved’s name using a subliminal priming paradigm.
DISCUSSION
The results are clear-cut. Two main results are important
Taken together, our results provide the first functional in this respect. First, we found that participants were
evidence that the subliminal presentation of a beloved’s faster to detect target stimuli when subliminally primed
name (as compared to a friend’s name) activates a spe- by a beloved’s name, and not when subliminally primed
cific pattern of brain activity, and these regions are more by a friend’s name. This phenomenon occurred espe-
active for people who are more in love. This network cially for word detection. This demonstrates that the
for implicit effects of a beloved’s name is partly concor- subliminal facilitation effect of love occurs at an associa-
dant with the love-related network demonstrated by tive level rather than a perceptual level. Women in love
previous studies that investigated the explicit mecha- are not inherently faster based on a general emotional
nisms of love. Nevertheless, our findings also reveal the arousal but they are faster because of the mental asso-
involvement of some distinct brain areas. Thus, our ciations they unconsciously created in their mind in
results may have important future implications for un- relation to their internal state of being passionately in
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derstanding the unconscious mental representation of love. This indicates that subliminal passionate/emotional
2021 on 18 May 2021
love in the brain. associations are sufficient to lead to automatic priming
Table 3. MNI Coordinates of Correlations between BOLD Responses for Love Minus Passion and Three Different Measures
of Love (PLS, 9-Point Scale, and Percent of Thoughts)
Coordinates PLS Scores 9-Point Scale Percent of Thoughts
Regions x y z t Love > Passion p Cluster Size p Cluster Size p Cluster Size
Occipitotemporal/ 48 50 24 4.65 3.11 .005 37 .005 23 – –
fusiform region
64 52 16 4.25 2.66 .003 115 .007 24 .008 49
Angular gyrus 64 50 22 4.35 2.65 .002 210 .009 40 .017 8
66 44 32 4.33 2.43 – – – – – –
1226 Journal of Cognitive Neuroscience Volume 19, Number 7on the basis of associative relatedness, which is defined results reinforce our behavioral results by demonstrating
as the extent to which the activation of one concept will dopaminergic-driven facilitation effects of both love and
call to mind another concept (e.g., Spruyt et al. 2004). passion on reaction times. Then, the subliminal presen-
Moreover, as expected, we found similar facilitation tation of a beloved’s name (as opposed to another
effects with a passion prime, in comparison with a friend motivator such as a passion’s descriptor, love > passion
prime. This highlights that the observed associative re- contrast) also show activation in higher order brain
latedness does not only call on emotional associations, areas, such as those known to be involved in conceptual
but also on motivation mechanisms. This is coherent thinking and metaphors (von Bubnoff, 2005). These
with Hebbian models of cortical language representa- differences of brain activation contrast with the equiva-
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tion, which suggest that the representations of words lent behavioral results we obtained for passion and love
are considered to include not only words’ visual forms, primes. Although this result might seem surprising, it is
but also their related memories (e.g., sounds, smells), coherent with Hebbian models of cortical language
and contextual encoding (Pulvermuller, 1996, 1999). representation, which suggest that the representations
Within such a Hebbian model, the behavioral priming of words may be segregated throughout cerebral hemi-
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effect arises when subliminal love or passion primes ac- spheres by their conceptual structures (Gisiger et al.,
tivate mental representations that are part of that par- 2000; Pulvermuller, 1996, 1999).
ticular state and, thus, implicitly modulates behavior, as
previously suggested for other facilitation priming ef-
Love and the Self
fects (Fergusson & Bargh, 2004; Innes-Ker & Niedenthal,
2002; Dehaene, Naccache, et al., 1998). In other words, Critically, love primes recruited bilateral fusiform and an-
our data suggest that the representation of a beloved’s gular gyri, two brain regions involved in integration of ab-
name may call for a goal-directed state sustained by stract representations (Arzy, Seeck, Ortigue, Spinelli, &
higher order mechanisms rather than a specific emo- Blanke, 2006; Jackson, Brunet, Meltzoff, & Decety, 2006;
tion without any motivational or reward components Saxe & Kanwisher, 2003; Blanke, Ortigue, Landis, &
(Bianchi-Demicheli et al., 2006; Aron et al., 2005; Aron & Seeck, 2002). Although some might attribute our effects
Aron, 1986). These selective facilitation effects also sug- to some bottom-up attention mechanisms because of
gest underneath associative mechanisms that may be due the specific salience of the subliminal stimuli (Anderson,
to implicit automatic spreading of activation from both 2005; Corbetta & Shulman, 2002; Anderson & Phelps,
emotional and motivational associations (e.g., Spruyt et al., 2001), this could not account for all brain activations.
2004; Musch & Klauer, 2003; Innes-Ker & Niedenthal, For instance, even if we agree that arousal mechanisms
2002). may take place when contrasting primes with different
salience (such as ‘‘love > friend’’ or ‘‘passion >
friend’’), automatic arousal mechanisms could not ex-
Unconscious Mental Representation
plain the difference of brain activation between two
of a Loved One
stimuli with equivalent salience, or at least with equiva-
Our fMRI results show that the subliminal presentation lent frequency of thoughts on target (such as love
of a beloved’s name (as compared to a friend’s name) primes and passion primes). Instead, the implication of
activates some cortical regions that are known to be these brain areas calls for higher order mechanisms. Our
also recruited during the conscious presentation of be- assumption is reinforced by the positive correlation
loved’s faces (Aron et al., 2005; Bartels & Zeki, 2000). between BOLD responses in these brain areas and the
Thus, our results suggest that the subliminal presenta- different measures of love (PLS scores, intensity, and
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tion of love-related stimuli correspond to variations in percent of thoughts). On the other hand, the absence
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neural response that extend beyond a visual memory for of correlation between brain activation in these brain
subliminal words. The subliminal presentation of a be- areas and the length of being in love underlines that the
loved’s name may implicitly activate the structural visual fusiform region and the angular gyrus do not seem di-
form of the word and also a more complex representa- rectly ‘‘love time dependent.’’ This is coherent with the
tion of the beloved. In agreement, our fMRI results high- only previous study that assessed this question (Aron
light that love calls for higher order motivational and et al., 2005) and showed changes in several regions as
reward mechanisms rather than a specific emotion the relationship changes, but not in the angular gyrus
per se. First, the overlap between the neural network and the fusiform regions. Instead, activity related to the
observed for love primes (love > friend contrast) and length of the relationship was found in the right insula,
that observed for passion primes (passion > friend con- the right anterior and posterior cingulate cortex, and the
trast) demonstrates that both love and passion primes right posterior cingulated/retrospenial cortex (Aron
recruited emotion/motivation/dopamine systems (Aron et al., 2005).
et al., 2005; Bartels & Zeki, 2000; Gisiger et al., 2000). In Moreover, a growing body of evidence demonstrates
accordance with the Dehaene–Changeux model as well that the angular and fusiform gyri not only call for
as the Aron et al. (2005) motivation assumption, these automatic attentional mechanisms but also higher order
Ortigue et al. 1227processes, such as episodic retrieval and conceptual set of brain areas for particular cognitive functions.
knowledge (Ashby & O’Brien, 2005; Giesbrecht, Camblin, Although that approach is appropriate for cognitive
& Swaab, 2004). For instance, love could be considered processes such as face recognition where the neural
as a learned response from episodic memories and substrates are well defined, the field of fMRI research
positive associative reinforcements that may be primary into love and abstract concepts is so novel that we
(such as pleasant feeling) and secondary (such as do not feel a region-of-interest approach is sensible. By
mental association between the beloved’s presence using a masking approach, we are able to obtain ade-
and good feelings; Brehm, Miller, Perham, & Miller, quate protection against false positives without limiting
2002; Smith & Queller, 2000; Carlston & Smith, 1996; our conclusions.
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Sternberg & Barnes, 1988). More critically, the angular Second, in our experiment the participants were only
gyrus is known to be involved in the abstract represen- women. This selection criterion could make the results a
tation of the self (Arzy et al., 2006; Blanke et al., 2002). bit different from those obtained in the two previous
This lets us speculate that the unconscious representa- studies that used a mix of genders (Aron et al., 2005;
tion of a beloved’s name is among others directed to the Bartels & Zeki, 2000).
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self. This is concordant with previous studies suggesting Finally, due to the absence of a ‘‘passionate scale’’ for
that intense lifetime achievements (e.g., love) are a cen- hobby, as was available for love, no correlation between
tral human motivation to ‘‘expand the self’’ (Aron & intensity of passion and BOLD responses could be done
Aron, 1986, 1996; Epstein, 1973; Rogers, 1969; White, in the present study. This area would benefit from the
1959). Our findings are also in agreement with theories development of standardized questionnaires evaluating
in social psychology suggesting that the expansion of the the different types and degrees of passion. This would
self involves two phases: expansion, then integration of be helpful to better understand the neural modulation
each new expansion by incorporating aspects (e.g., new of a passion with respect to its intensity.
skills, attitudes, resources, behaviors) of another into Our study of subliminal love primes is the first fMRI
the self (Aron & Aron, 1986, 1996; Hatfield & Walster, investigation of this phenomenon, which is considered
1978; Epstein, 1973; Rogers, 1969; Bataille, 1962; White, to be both a concept and a motivational factor. Further
1959). The angular gyrus is important in (a) integration work will be needed to distinguish between different
of abstract representations of others ( Jackson et al., types of passions (for objects or for hobbies) and differ-
2006), (b) social cognition related to the ability to rea- ent types of love (for a partner or a child) and to better
son about the contents of mental states, such as de- understand the conceptual framework underlying love
sire (Saxe & Kanwisher, 2003), or both. In addition, the representations in the brain.
temporoparietal junction is an association brain area
considered pivotal in carrying out cross-modal informa-
Conclusion
tion (Bremmer, Schlack, Duhamel, Graf, & Fink, 2001;
Calvert, Campbell, & Brammer, 2000). This is of particu- The present study reveals that the neuroscience of love
lar importance for the concept of love, which is based might provide not only essential clues for understanding
on multidimensional components (Sternberg & Barnes, emotion and motivation systems, but also how one’s
1988; Hendrick & Hendrick, 1986). Because ‘‘a love unconscious may be enhanced by desire.
experience will not expand the self if it cannot be inte-
grated’’ (Aron & Aron, 1986; James, 1890/1950), this brain
Acknowledgments
area might be crucial for self-expansion by integrating dif-
ferent love-related sensations and extracting a common, We thank Prof. M. Gazzaniga for his helpful comments on a
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abstract representation from them. previous version of the manuscript. This study was supported
2021 on 18 May 2021
by the Swiss National Foundation for research in Biology and
Medicine (grant 1223/PASMA 111563/1). The experiment was
Possible Limitations and Future Directions carried out using Matlab 7.0.1 and Cogent 2000 developed at the
Laboratory of Neurobiology and the Wellcome Department of
There are some factors that restrict our interpretation Imaging Neuroscience, University College London. The authors
of the data in this study and that could be examined declare that they have no competing financial interests.
more closely in the future. Because there are not many Reprint requests should be sent to Scott T. Grafton, Sage Center
previous studies of the neural basis of love and none for the Study of the Mind and Department of Psychology,
about the neural basis of passion, our study constitutes Building 251, Room 3837, University of California, Santa Barbara,
CA 93106, or via e-mail: grafton@psych.ucsb.edu or ortigue@
a first step and includes some limitations. First, be- psych.ucsb.edu.
cause no study has previously unraveled the implicit
neural basis of love and passion, we did not feel justi-
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