Andreas Bartels and Semir Zeki of the Wellcome Department of Imaging Neuroscience, University College London have found using Functional Magnetic Resonance Imaging (fMRI) that love turns down activity in some areas of the brain in part so that we will not see flaws in the object of our affections.
However the key result was that it's not just that certain shared areas of the brain are reliably activated in both romantic and maternal love, but also particular locations are deactivated and it's the deactivation which is perhaps most revealing about love.
Among other areas, parts of the pre-frontal cortex – a bit of the brain towards the front and implicated in social judgment – seems to get switched off when we are in love and when we love our children, as do areas linked with the experience of negative emotions such as aggression and fear as well as planning. The parts of the brain deactivated form a network which are implicated in the evaluation of trustworthiness of others and basically critical social assessment.
The scientists recruited mothers and used pictures of their children as well as pictures of other people and watched how the women responded to the pictures. The researchers also reanalysed data they had previously collected for previously published research involving women in love.
He said: "Our research enables us to conclude that human attachment employs a push-pull mechanism that overcomes social distance by deactivating networks used for critical social assessment and negative emotions, while it bonds individuals through the involvement of the reward circuitry explaining the power of love to motivate and exhilarate."
Bartels has the full text of the research paper on his web site. When we fall in love we become blinded to faults and at the very same time we become flooded with rewarding feelings. (PDF format)
Romantic and maternal love are highly rewarding experiences. Both are linked to the perpetuation of the species and therefore have a closely linked biological function of crucial evolutionary importance. Yet almost nothing is known about their neural correlates in the human. We therefore used fMRI to measure brain activity in mothers while they viewed pictures of their own and of acquainted children, and of their best friend and of acquainted adults as additional controls. The activity specific to maternal attachment was compared to that associated to romantic love described in our earlier study and to the distribution of attachment-mediating neurohormones established by other studies. Both types of attachment activated regions specific to each, as well as overlapping regions in the brain’s reward system that coincide with areas rich in oxytocin and vasopressin receptors. Both deactivated a common set of regions associated with negative emotions, social judgment and ‘mentalizing’, that is, the assessment of other people’s intentions and emotions. We conclude that human attachment employs a push– pull mechanism that overcomes social distance by deactivating networks used for critical social assessment and negative emotions, while it bonds individuals through the involvement of the reward circuitry, explaining the power of love to motivate and exhilarate.
Maternal and romantic love share a common and crucial evolutionary purpose, namely the maintenance and perpetuation of the species. Both ensure the formation of firm bonds between individuals, by making this behavior a rewarding experience. They therefore share a similar evolutionary origin and serve a similar biological function. It is likely that they also share at least a core of common neural mechanisms. Neuro-endocrine, cellular and behavioral studies of various mammalian species ranging from rodents to primates show that the neurohormones vasopressin and oxytocin are involved in the formation and main-tenance of attachment between individuals, and suggest a tight coupling between attachment processes and the neural systems for reward (Carter, 1998; Insel and Young, 2001; Kendrick, 2000; Pedersen and Prange, 1979). This is confirmed by lesion, gene expression and behavioral studies in mammals (Numan and Shee-han,
Perhaps it is not a coincidence that many lovers call each other "babe" and there is a great deal of overlap between the brain's feelings of romantic and maternal love.
Note that regions rich with vasopressin receptors are involved in maternal and romantic love. This brings us to another recent report where scientists have found that gene therapy to deliver vasopressin receptor genes into the ventral pallidum part of the brain made male meadow voles become uncharacteristically monogamous.
ATLANTA -- Researchers at the Yerkes National Primate Research Center of Emory University and Atlanta's Center for Behavioral Neuroscience (CBN) have found transferring a single gene, the vasopressin receptor, into the brain's reward center makes a promiscuous male meadow vole monogamous. This finding, which appears in the June 17 issue of Nature, may help better explain the neurobiology of romantic love as well as disorders of the ability to form social bonds, such as autism. In addition, the finding supports previous research linking social bond formation with drug addiction, also associated with the reward center of the brain.
In their study, Yerkes and CBN post-doctoral fellow Miranda M. Lim, PhD, and Yerkes researcher Larry J. Young, PhD, of the Department of Psychiatry and Behavioral Sciences at Emory University's School of Medicine and the CBN, attempted to determine whether differences in vasopressin receptor levels between prairie and meadow voles could explain their opposite mating behaviors. Previous studies of monogamous male prairie voles, which form lifelong social or pair bonds with a single mate, determined the animals' brains contain high levels of vasopressin receptors in one of the brain's principal reward regions, the ventral pallidum. The comparative species of vole, the promiscuous meadow vole, which frequently mates with multiple partners, lacks vasopressin receptors in the ventral pallidum.
The scientists used a harmless virus to transfer the vasopressin receptor gene from prairie voles into the ventral pallidum of meadow voles, which increased vasopressin receptors in the meadow vole to prairie-like levels. The researchers discovered, just like prairie voles, the formerly promiscuous meadow voles then displayed a strong preference for their current partners rather than new females. Young acknowledges many genes are likely involved in regulating lifelong pair bonds between humans. "Our study, however, provides evidence, in a comparatively simple animal model, that changes in the activity of a single gene profoundly can change a fundamental social behavior of animals within a species."
According to previous research, vasopressin receptors also may play a role in disorders of the ability to form social bonds, such as in autism. "It is intriguing," says Young, "to consider that individual differences in vasopressin receptors in humans might play a role in how differently people form relationships."
And, Lim adds, past research in humans has shown the same neural pathways involved in the formation of romantic relationships are involved in drug addiction. "The brain process of bonding with one's partner may be similar to becoming addicted to drugs: both activate reward circuits in the brain."
The researchers' next step is to determine why there is extensive variability in behaviors among individuals within a species in order to better understand the evolution of social behavior.
Well, consider the possibilities. Want to solve the soaring divorce rate problem? Bioengineer a virus to infect the population to deliver the vasopressin gene into the ventral pallidum at the base of the brain. After years of ineffective moralizing and countless social science studies the problem of disintegrating marriages would be solved.
Another possibility would be the use of such a gene therapy by someone who is in love to make the object of their affections primed to fall in love. Of course, the lover surreptiously treated with emotional brain engineering genetic therapy might fall in love with the next person they accidentally bump into in the supermarket. So such a gene therapy would not be foolproof once it becomes feasible.
But since love causes brain changes that have some similarities to what addictive drugs do to the brain an argument can be made for the proposition that love is just another form of addiction for which humans need an effective treatment that will end the craving.
In their research, funded by the National Institute of Mental Health, Larry Young, PhD., associate professor of psychiatry and behavioral sciences at Emory University School of Medicine and an affiliate scientist at Yerkes National Primate Research Center; graduate student Miranda Lim; and Anne Murphy, PhD., associate professor of biology at Georgia State University, examined the distribution of two brain receptors in the ventral forebrain of monogamous prairie voles that have been previously tied to pair bond formation: oxytocin (OTR) and vasopressin V1a receptor (V1aR). Using receptor audiographic techniques, the scientists found that these receptors are confined to two of the brain's reward centers, the nucleus accumbens and the ventral pallidum. V1aR receptors, which are thought to be activated in the male vole brain during pair bond formation, were confined largely to the ventral pallidum. OTR receptors, which play a crucial role in pair bond formation in females, were found mainly in the nucleus accumbens.
Perhaps a person with more oxytocin and vasopressin receptors finds life to be more rewarding in general. But are they more or less prone to drug addiction?
|Share |||Randall Parker, 2004 June 17 02:39 AM Brain Love|