Our Brains Have Chemistry: What’s Love Got to Do, Got to Do With It?

            Love is a wonderful phenomenon that almost everyone can relate to despite the challenging, perhaps even impossible task of defining it or describing its many different interpretations and implications. Curiously, the multi-dimensional construct of love leaves many of us with pressing questions, one of which involves the obvious notion that love must somehow be influenced by internal mechanisms, but which ones and how? Logically, it has been stated that love functions biologically to ensure the survival of a species through social attachment and reproduction, so it is no surprise that science has found great interest in explaining the biology behind love. As researchers are beginning to find out, love is much more than a complicated, virtually universal emotion. In fact, this relatively recent realm of study reveals very interesting findings that yield neurobiological support for some of the interesting behaviors many of us present with while smitten, such as irrational tendencies, obsessive thinking about our significant other, and feelings of euphoria. Similarly, research is developing a greater understanding of maternal love, with prolific observations that mother and child attachment shares both distinguished and common brain pathways with romantic love.

            What is it about certain people that draw us to them? As many of us have discovered, attraction is governed by several factors that we share in common with significant others such as similar interests, socioeconomic levels, and family backgrounds (1). Environmental factors which develop our character often intertwine with biological factors that shape our temperament, and together these influences make up who we are and who we may be romantically drawn to. Less commonly known, however is the role hormones play in governing whom we are attracted to. Elvis was somewhat correct when he sang, “I can’t help falling in love with you.” It’s true: some aspects of attraction are uncontrollable because they are biologically predetermined. For example, according to research, every individual has what has been coined a “chemical profile” for hormone composition including distinct levels of estrogen, testosterone, dopamine, and serotonin. Interestingly, we are attracted to individuals that have different, yet complimentary profiles to our own (1). Perhaps the saying that opposites attract isn’t as far off as some of us may have previously thought. Similarly, body odor plays a role in determining whom we are romantically attracted to and such a preference is in part influenced by gender and sexual orientation. One compelling study (1) asked participants of different genders and sexual orientations to choose between odors based on liking and each picked the odor that corresponded to their preferred gender and sexual orientation. This odor is determined by a variety of factors, one of which is a cluster of genes called the major histocompatibility complex, or MHC (1). Much like a fingerprint, there are so many variations of MHC that no two are alike. I wonder, optimistically, if perhaps this finding can be substantial enough to support the theory that sexual orientation is in part biologically driven since MHC is genetically determined and plays a significant role in dictating whom we are attracted to.

            Neurobiologists are also interested in distinguishing among certain brain circuits to improve our understanding of different forms of love as developing from separate, yet often overlapping structures that clearly possess biological significance. One such circuit determines our sex drive which motivates us to seek out our partners and eventually reproduce with them. Romantic love involves another complex brain circuit, which involves attraction factors and euphoric feelings. Last but not least is the attachment circuit which manages the comfortable, less infatuated stage of romantic love and the nurturance associated with maternal love. All three circuits necessitate two important hormones: oxytocin, also known as the hormone of love, and vasopressin (1).

            Oxytocin is extremely significant to the bonding process experienced by humans and some animals, produced by the hypothalamus and stored in the pituitary gland. It is discharged into the blood during several activities, all of which facilitate bonding and attachment (2). For example, oxytocin is released during orgasm (4) which explains the connection and trust people feel with their intimate partners after sex. Oxytocin is also released by women in labor to induce the contractions of myoepithelial tissue so that the baby may be delivered, and is likewise involved in the contraction of cells in the breast to initiate milk flow during lactation (4). Not surprisingly, milk also contains high levels of oxytocin, thereby reinforcing the attachment between mother and child in the first year after birth. For those experiencing romantic love, oxytocin influences partner preference and may play a role in parasympathetic autonomic functions, such as increased respiration, blood pressure, and cardiac output (2). So in a way, our hearts really might occasionally skip a beat when we see or touch our sweetheart! Also of importance is oxytocin’s role in inhibiting sympathoadrenal and stress response activity. In other words, oxytocin release is linked to anxiety level reduction, perhaps making love the ultimate stress buster. Undoubtedly, vasopressin is just as critical to this discussion as oxytocin. This hormone, released by the pituitary gland, is likewise involved in attachment and bonding processes such as partner selection and attraction and sexual behaviors (4). By now it has become clear that brain regions that contain oxytocin and vasopressin receptors are highly activated by both romantic and maternal love.

            Although romantic love has frequently been regarded as a constellation of emotions, it has also recently been distinguished as orienting around the body’s motivation system, partially designed to enable individuals to establish and maintain close relationships with preferred mating partners. Fascinatingly, areas of the brain which are activated when people are in love are the very same areas that are involved in the brain’s motivation and reward system including cortex structures such as the medial insula, anterior cingulated, and hippocampus, as well as subcortex structures including parts of the striatum and the nucleus accumbens (5). These areas are highly concentrated with dopamine which is critical to the control of emotional response and the ability to feel pleasure and pain. Related to the reward system is the ventral tegmental area (VTA), located near the base of the brain, which has been affectionately coined the “mother-load” for dopamine making cells (3). These neurons project to other areas in the brain including the posterial dorsal caudate nucleus and its tail, both of which are central to reward and motivation systems. Dopamine is released by the hypothalamus, a brain structure which links the nervous and endocrine systems, and when released dopamine causes a feel-good state (2), which logically corresponds to that warm-and-fuzzy feeling we so often associate with being in love.  

            One particularly attractive study (3) collected data on brain activity while love-smitten participants performed two tasks: one which involved looking at a photograph of their significant other for 30 seconds and another which involved looking at a neutral photograph of an acquaintance for 30 seconds. Distraction was initiated for 40 seconds between tasks by asking participants to count backward from a large number in increments of seven in order to control for any overlap between task reactions. Functional magnetic resonance imaging (fMRI) machines took pictures of the participants’ brains during each task. Results provided evidence of increased blood flow to, or activation in, certain areas of the brain associated with love when asked to look at the photograph of a significant other. One specific region appeared to be central to the experience of being in love and looking at photograph of a loved one: the caudate nucleus. Clearly this study supports previous research described above. Even more remarkable was the fact that the more passionate participants were about their significant other, the more active their caudate was while focusing on the photograph of their sweetheart.

            Undoubtedly you’ve heard the phrases, “Love is blind,” or “I’m madly in love,” and of course there’s Beyonce’s chart topping hit “Crazy in Love.” Many of us have experienced such feelings, but for anyone left questioning the somewhat crazy tendencies associated with being in love, science has offered a persuasive and logical explanation. As it turns out, our often irrational behaviors expressed during states of love are justified by a pattern of cortical deactivation (5). The frontal cortex, parietal cortex, and parts of the temporal lobe are all normally involved in negative emotion, among other activities. However, studies have shown that these areas are less active in romantic and maternal states, which can in part explain our irrationality and our suspension of judgment of people we love. Therefore, it is only natural to view your honeybunch through rose colored glasses despite the fact that he chews with his mouth full or sings Eric Clapton songs terribly out of tune.

            As the Ohio Players might argue, “Love is like a rollercoaster baby, baby.” This should not come as a surprise to one who has not yet experienced the incredible phenomenon. When in love, hormone levels climb and fall within a short period of time, and it follows that many individuals may feel the emotional effects of such swift changes (2). Science seeks to explain the function of such modifications and it is widely accepted today that hormone level alterations are necessary for the support of different states that allow us to initiate and later maintain good relationships, thus perpetuating the romantic and attachment circuits mentioned earlier. So if in the first few months of a budding relationship you begin to feel as though you just got off Great Adventure’s Nitro, take comfort in knowing its not you; it’s biology.

            By studying neural correlates of subjective mental states, we are able to draw conclusions about complex emotions such as love, which turns out to be partly driven by biology. Important factors dictate who we are attracted to and who we fall in love with, but compatibility is obviously not completely consciously selected for. Biology is a large contributor to the experience of love. It can cause us to gravitate toward certain types of people, act irrationally in the name of love, and can even color our judgment of people we might otherwise criticize. Perhaps the chemistry of love can shed some light on why some of us have trouble getting over loved ones, or can serve to explain the indescribable, indestructible bond between a parent and child. Clearly recent science has discovered many insights into the complicated yet remarkable experience of love, but many questions still remain. Can love truly last forever? Is it possible to romantically love more than one person at once? Is there a magic formula we can take to biologically “get over” past lovers who continue to plague our present? These are just a few of the interesting queries individuals have posed; hopefully, as our understanding of the science behind relationships evolves, many such questions will be answered and a comprehensive understanding of what was once a complex mystery will finally be unveiled.

References

(1) Doheny, Kathleen. (2008). Love on the brain. From Web MD Special Report:

http://www.webmd.com/sex-relationships/modern-love-8/biology-of-love

(2) Esch, Tobias, Stefano, George B. (2005). Neurobiology of love. From Neuroendocrinology Letters:

http://www.nel.edu/pdf_/26_3/260305R01_15990719_Esch--Stefano_.pdf

(3) Fisher, Helen. (2004). Your brain in love. From Time Magazine: http://www.time.com/time/printout/0,8816,993160,00.html

(4) McManamy, John. (2008). The Brain in love and lust. http://www.mcmanweb.com/love_lust.html

(5) Zeki, S. (2007). The Neurobiology of love. From FEBS Letters:

 http://linkinghub.elsevier.com/retrieve/pii/S0014579307004875