Pique the Geek 20111120: The Neurochemistry of Love

(9 pm. – promoted by ek hornbeck)

The subject of love has been investigated by philosophers, writers, dreamers, theologists, and a whole host of others throughout the ages.  With the advent of the “science” of psychology, the question was even further muddled.  Please do not get me wrong, I have the utmost respect for ethical psychologists, but some of the hypotheses that the likes of Freud proposed were just plain wrong and just confused the issue.

We are just beginning now to solve some of the puzzle, and it turns out that there is quite a lot of biochemistry (and not just neurochemistry) that is involved.  With modern chemical analytical techniques, precise measurements of various neurotransmitters can be made, and with functional magnetic resonance imagining (fMRI) actual images of the human brain in action can be had.

Using a combination of observations about how people behave during different stages of love and some results from these methods, let us take a look about how love works, how it can be one of the most exhilarating experiences that is, and how it can be so terribly hurtful when it goes wrong.  Are you ready?

First, let us define what kind of love about which we speak.  Ancient Greek had different words for different kinds of love.  Agape is the kind of love described in the Bible, the love of others as oneself.  However, it can have a broader meaning and certainly there is a considerable amount of this kind of love in stable, loving relationships.

Philia is the kind of love that is experienced as love of country, love of family, and other kinds of love that provide a practical payback to the one who loves.  This involves a sense of community and mutual support.  There is also a considerable component of philia in loving relationships of couples.

Then there is storge, like the feelings betwixt parents and children or siblings towards each other.

Xenia is the kind of love that we have for friends, but the original Greek definition was more ritualistic because in ancient Greek culture, hospitality was much more important than in contemporary culture.  The usage that I have in my mind is that friendship is sort a combination of agape and xenia.

Finally, there is eros, which is the passionate kind that lovers show towards each other (if they are lucky and the object of desire returns the feelings).  Eros is the kind of love that couples, after they begin to develop towards each other, usually first experience.  It is also the most unpredictable and volatile of the bunch, and it the kind that makes people crazy, either in a good or a bad way.

There are other definitions, but these serve as well as any.  The next step is to study the “stages” of love and try to associate them with biochemistry.  Typically, once two people become attracted to each other, they go through a period that is mostly eros, also called lust.  This is more common in younger people, but I am convinced that there is a significant portion of lust even in older couples who are first forming a relationship.  Here is why I say that:

I have personally observed older people, in their 70s and even 80s, show behavior that is typically thought of for teenagers.  They begin to develop feelings for someone and their behavior changes.  They pay more attention to their appearance, they “light up” when they see that special someone, and they sort of go a little nuts.  My own father did that very thing a few years after my mum died.  Often the manifestation is not as strong as in younger, and thus less experienced, people but I know for a fact that it happens.

Before we get to the neurochemistry, here is an fMRI scan of the same person’s brain when they see am image of a loved one (on the left) and a friend (on the right).  Note that completely different areas of the brain are activated.  Caution, this is a 6+ MB .pdf file.

Here is another that is not a .pdf.  Note that different regions of the brain are involved for the most part, and that the romantic love areas are brighter, denoting more activity.

Here is even a better one, although not an actual fMRI scan, but an illustration of one.  I like this one because it labels different parts of the brain and relates them to some of the neurotransmitters that I mention herein.

Interestingly, studies have shown that sex hormones are increased during this stage, so lust is really a good word for it.  But increase in sex hormone levels are not sufficient to cause some of the crazy behavior.  Animal studies have indicated that other chemicals are also elevated during this phase, and continue to be elevated for much longer than the elevated levels of sex hormones.  The sex hormones generally return to normal levels in a few weeks of months, while the other materials continue to be elevated for well over a year, sometimes as long as three years.  But they too return to previous levels eventually.  This is why many couples “fall out of love” after about that amount of time.

One of these materials in the neurotransmitter dopamine, our old friend from my Drugs of Abuse ten part series here about a year ago.  Dopamine is quite correctly called the pleasure neurotransmitter because without it, it is not possible to trigger the mesolimbic reward center in the brain.  When more dopamine is present, you feel happy.  Many drugs of abuse are addictive because they trigger a dopamine cascade that is higher than normal, but the effect wears off after a while, depending on the drug.  Then there is the “crash” that happens when the concentration of dopamine decreases.

It is also known that the intensity of the good feelings is not only related to the concentration of dopamine, but also to the time derivative of the dopamine concentration.  In mathematical symbology, the intensity of the good feelings are functions of both [dopamine] and d[dopamine]/dt where the brackets indicate concentration of dopamine, in keeping with standard physical chemistry notation.

Thus, it is possible to begin to feel bad even with elevated dopamine concentrations if the concentrations are decreasing, even though elevated.  How many people in love have you known that felt lousy because they did not get their “fix” of spending time with their love interest?  Just about people in the early few years of being in love are that way.  That is why couples like that are often described as “inseperable”.

Interestingly, dopamine also inhibits the release of prolactin, the hormone responsible for, amongst other things, providing the sense of gratification after having sex.  At first this sounds sort of contraintuitive, but it makes perfect sense.  Couples tend to have sex more often during the first few years, and this is consistent with not becoming as completely fulfilled after a sexual encounter as they otherwise would have been.  Couple who have been together for several years tend to have sex less often, but it is often more fulfilling when they do have it.  So it seems that it is more than just getting to know one’s partner’s body after a few years that make for “better” (more fulfilling) lovers.

Another neurotransmitter involved is norepinephrine.  This neurotransmitter also has other effects, amongst them increasing heart rate and blood pressure.  This is part of the reason that newer couples get those symptoms when they see each other after being away, or when they engage in romantic activity, which might be as innocuous as holding hands.  It also modulates mood, and some modern antidepressants suppress the reuptake of norepinephrine.  One norepinephrine receptor is strongly bound by MDMA, commonly called the “love drug”.  MDMA is of a class of drugs called empathogens, meaning that it increases feelings of empathy towards others in people taking it.

Another neurotransmitter that is elevated during those first three or so years is serotonin, which is very strongly associated with mood.  Most modern antidepressants act by preventing reuptake of serotonin, thus making more of it available in the synapses, elevating mood.  This is largely why couples early in their relationships are always so happy.  It turns out that serotonin is fairly slow acting in comparison with dopamine, so even with elevated levels of serotonin it is possible for new couples to become despondent after a fight or a breakup.

While not a neurotransmitter, nerve growth factor is also elevated during the early phases of love.  This factor is essential for the health of neurons, and there are some indications exist that it is also associated with longer lifespans.  However, since it is one of the materials that are only elevated temporarily, that does not seem to be a contributor the the statistically derived conclusion that couples in long term, committed relationships tend to live longer.

So far we have discussed the materials that are elevated for only a relatively short time after a couple falls in love.  After the lust stage, lasting for a few months or a little longer, there is the stage that is caused by the materials just mentioned that lasts for a couple of years of a little longer, generally called the attraction phase.  What about after that?  If there were not a more lasting change, most couples would split within a few years (and many do).

There are at least two different bonding hormones.  For females, the main one identified so far is oxytocin, a nonapeptide hormones with a wide range of effects, both mental and physical.  This hormone does not decrease with time, but acts a bit differently than the others mentioned previously in that some of the effects seem to be permanent even after only a single event, and that this bonding is reinforced after each event.  The event in question is normally sexual intercourse, but animal studies show that artificially introduced oxytocin has the same effect.

It has been determined that in both males and females oxytocin levels are raised after periods of activities not involving sex.  For example, after half an hour of a person petting a dog, higher levels of oxytocin are found in both.  This may explain the interesting interspecies bond that dogs and most humans share.  Oxytocin is also released in both males and females during activities like hand holding, long hugs, and even just lying quietly together even if sex is not involved.  Since the levels do not decrease with time, but are constantly being reinforced with each encounter.

In males, the hormone vasopressin, also a nonapeptide and structurally similar to oxytocin, seems to be the more important of the two.  It also disposes the male to bond with the female, and is also released during sexual activity.  Also like oxytocin, it controls many other functions in the body.

Oxytocin is also critical for the mother/child bond.  Animal studies show that ewes treated with an oxytocin antagonist do not bond with their lambs.  On the other hand, giving oxytocin to a ewe that is not pregnant will cause it to bond with a stray lamb.  During birth, large amounts of oxytocin are released, and one of the primary functions of it is to trigger the “let down” reflex to that milk begins to flow.  Suckling the nipples also causes oxytocin to be released, as when a child is ready to feed.  Some women become so acutely aware of their baby that merely hearing the “hungry cry” will cause oxytocin release and start the letdown reflex.

Repeated nipple stimulation can also cause milk to be produced through a different mechanism.  Many years ago the former Mrs. Translator and I got a kitten who had just been weaned, but too early.  The kitten and her dog took up with each other and the kitten would try to get milk.  After a week or so of this, the dog, which had never had pups, actually developed milk for the kitten.  This is a true story.

Fortunately or unfortunately, depending on one’s viewpoint, these neurochemical changes are not necessarily one time things.  It is possible for people to fall in love repeatedly with different people (sometimes with the same person; I had a cousin who married the same woman three times).  This can be disastrous for established couples, causing untold heartache for the partner who is in the bonding stage and the other partner starts a new cycle with someone else.  On the other hand, it can be a source of great joy for those who have lost a partner for some reason or another, because the potential for love always is there.

There also seems to be a genetic relationship, at least in males and almost certainly also in females, betwixt long term faithfulness and the distribution of vasopressin receptors in the brain.  It turns out that some men have far fewer receptors than others, and there seems to be a statistical correlation betwixt having more receptors and more stable long term relationships.  Interestingly, in the animal kingdom most mammals are not monogamous for life, but a few are.  Sure enough, the monogamous ones have a receptor distribution more like those in the human, a generally monogamous creature.  I suspect that there are similar differences in oxytocin receptors in females.  Some mothers never bond with their baby.

Now, do not get the idea that I believe that love is nearly so clinical and easily explained.  There are hundreds of other facets to love that are almost certainly NOT purely neurochemistry.  For example, just seeing someone for large amounts of time every day makes them accustomed to each other.  In healthy relationships, the anticipation of responses in the partner is endearing.  In not so good ones, such actions that are anticipated become annoying when they happen.  However, being accustomed to someone allows the mate to anticipate the needs and desires of the other and to help fulfill them.  Sometimes this is called “getting in a rut”, but I think that some sort of routine, for lack of a better word, is probably essential for a good long term relationship.  Everyone likes surprises from time to time, but most people are not pleased with a constant stream or surprises from a mate because it is disruptive.

There are many more aspects to love than anyone fully understands, even though the nature of it has been pondered by minds great and small since the rise of civilization.  I hope that my little piece here helps to demystify at least one aspect of the wonderful, awful, exhilarating, debilitating, happy, and sad thing that we call love.  Love, capable of taking us to the height of ecstasy and to the depths of despair.  Love, when within a healthy relationship makes two people much greater than the sum of their parts, but when within a bad relationship is destructive more than any other force.  Love, causing the strange and wonderful sensations when seeing or hearing the object of affection.  Love, causing dreadful reactions when not returned.  Love, reign o’er me!

Well, you have done it again!  You have wasted many more einsteins of perfectly good photons reading this account of something that no one fully understands.  And even though Newt Gingrich realizes that too many lust cycles has sunk is chance at being President when he reads me say it, I always learn much more than I could possibly hope to teach by writing this series.  Thus, please keep those comments, questions, corrections, and other feedback coming.  Tips and recs are also quite welcome!  I shall stay around tonight as long as comments warrant and shall return after Keith’s show tomorrow for comments that come after I get to the bed.

Warmest regards,

Doc, aka Dr. David W. Smith

Crossposted at

The Stars Hollow Gazette

Daily Kos, and

firefly-dreaming