Heterosexual or homosexual, male or female, it’s all the same as far as the brain systems that regulate romantic love are concerned, according to a new study from University College London (UCL), where researchers examined functional magnetic resonance imaging (fMRI) brain scans of volunteers while they looked at the faces of their lovers.

Drs Semir Zeki and John Romaya from the Wellcome Laboratory of Neurobiology at UK’s UCL published their findings, which followed from earlier work on differences between romantic and maternal love, in the 31 December 2010 issue of PLoS ONE.

In their introduction they explain that this study is a continuation of previous work on brain systems that appear to be critical for romantic love. Their inspiration came from reading world literature on love, both Western and Oriental, where characters in love appear to have the same sentiments, whether male or female, and regardless of sexual orientation.

Zeki, Professor of Neuroesthetics at UCL, told the media that:

“Passionate romantic love is commonly triggered by a visual input and is an all-consuming and disorienting state.”

He said previous research has shown that although the emotion is complex, when you look at brain images of a person who is viewing the face of someone they are passionately in love with, the patterns occur only in a few, though richly connected, regions of the brain.

“This limitation made it plausible to suppose that we could detect any differences relatively easily,” he and Romaya write.

Other studies have described physical differences between homosexual and heterosexual brains, for example in the size of the hypothalamus and the degree of asymmetry of the two hemispheres.

But these have been described in the context of sexual arousal and not in response to the “sentiment of love”, they add, going on to propose that given the profound similarities in the expressions of the sentiment of love, then one would also observe “no differences when females or males, or heterosexual or homosexual subjects, viewed the face of their loved partners”.

For the study, Zeki and Romaya invited 12 women and 12 men (6 heterosexual and 6 homosexual in each case), aged 19 to 47, to look at pictures of their lovers and pictures of friends of the same sex as their lovers but to whom they reported feeling romantically indifferent, while they took fMRI scans of their brain activity.

All the participants said they were passionately in love with their romantic partners and were in a sexual relationship with them. The length of the relationships varied from 4 months to 23 years.

(There were originally 28 volunteers, but the researchers excluded 4 for various reasons, for instance one reported deep underlying problems in the relationship and another fell asleep during the scanning).

After the scans, participants gave a Kinsey rating of their sexual orientation on a scale of 0 (exclusively heterosexual) to 6 (exclusively homosexual). Of the 24 subjects, half were either exclusively heterosexual or homosexual, while the other half, whose rating fell in between, nevertheless declared their relationship to be either heterosexual or homosexual, wrote the researchers.

The participants also completed Passionate Love Scale (PLS) questionnaires, to attempt to quantify their feelings about their lover.

To prepare the images the researchers used Cogent 2000 and Cogent graphics, a system developed at UCL for helping researchers design experimental stimuli for brain imaging and psychophysical studies.

To make all the images as uniform as possible, so the only differences between them were the people portrayed, the photographs, which the participants provided themselves, were digitized, converted to grayscale and edited to remove features like earrings, scarves and background, which was replaced by a flat mid-grey tone. They were then also normalized in terms of visual area and average brightness.

The fMRI results showed:

A very similar pattern of activation between the different groups.

The pattern showed that both the cortical and sub-cortical areas were active.

The main areas of activity were areas known to be rich in dopaminergic (“feel good”) neurotransmitter activity.

These areas included the “hypothalamus, ventral tegmental area, caudate nucleus and the putamen, as well as the insula, hippocampus and anterior cingulate cortex”.

There was also extensive de-activation of large parts of the cerebral cortex when the participants viewed images of their lovers, and this was independent of gender and sexual orientation.

Dopaminergic activity is strongly linked with the activity of other neurotransmitters, such as those involving oxytocin and serotonin, which scientists believe play an important role in regulating emotion and bonding in relationships.

The de-activated areas included parts of the temporal, parietal and frontal cortex, and other cortical areas that scientists believe play a critical role in judgement, and this finding may explain why we often appear less judgemental about those we love, lending support to the old saying “love is blind”.

Zeki and Romaya concluded that:

“The pattern of activation and de-activation was very similar in the brains of males and females, and heterosexuals and homosexuals. We could therefore detect no difference in activation patterns between these groups.”

They commented that the world of literature is also “very uniform in this regard”, both Western and Oriental literature, and regardless of whether the relationship is same or opposite sex.

Central to the sentiment of passionate love are two recurring themes, they write:

“… the desire to be united with the lover and to be annihilated with, and in, the lover.”

The themes are “forcefully there” in “Wagner’s Tristan und Isolde, in the Farsi poetry of Rumi and Hafiz, the Arabic-Azeri legend of Majnun and Leila, the Rime of Michelangelo and in the double suicide shinju tradition in Japan”, and they also list other sources including Hindu legends, Sufi love literature, and Shakespeare’s sonnets.

It was the presence of this “profound ambiguity”, whereby the sentiment can be read in the context of same or opposite sex, “regardless of the authors’ intentions”, that prompted the researchers to carry out the study and find in conclusion a similar pattern in brain images:

“Here we have shown that, with the methods currently available to us and using perhaps overly conservative criteria, we could not detect any differences relating to the expression of the sentiment of love in the same or opposite sex context, either in the areas activated or in the intensity of activation within them.”

However, they also pointed out it does not mean that differences do not exist, but they are perhaps best “sought elsewhere than in the experience of the sentiment of love when viewing the face of a loved partner”, such as in the sexual counterpart to love.

“The Brain Reaction to Viewing Faces of Opposite- and Same-Sex Romantic Partners.”

Zeki S, Romaya JP

PLoS ONE, 5(12): e15802; published online 31 Dec 2010

DOI:10.1371/journal.pone.0015802

Written by: Catharine Paddock, PhD