This Is Your Brain on Sex (8 page)

It is also possible that these raised cortisol levels simply represent plain old garden-variety stress. You may be head over heels, but can you be certain your intended feels the same way? Anyone who is in the early days of a relationship can
relate to overthinking the whole loves-me, loves-me-not thing. It can be a source of some consternation. As I said, why Marazziti saw these enhanced levels of cortisol is up for debate. It could be due to some vestigial stress response to a hundred-million-year-old attachment system, new relationship concerns, or something else altogether. We may never know.

As to Marazziti’s findings regarding testosterone and FSH, she has no hard-and-fast answers. In a paper published in
Psychoneuroendocrinology
about the study, she wrote, “All subjects presented this finding, as if falling in love tended temporarily to eliminate some differences between the sexes, or to soften some male features in men and, in parallel, to increase them in women. It is tempting to link the changes in testosterone levels to changes in behaviors, sexual attributes or, perhaps, aggressive traits which move in different directions in the two sexes, however, apart from some anecdotal evidence, we have no data substantiating this which would justify further research.” So we could say it makes women more open to sex and men more open to cuddling, or some other meeting of the proverbial minds between the two genders, but the truth is, we just don’t know more than the fact that these levels change—and only in the early stages of romantic love. By the time these individuals get into a stable, long-term relationship, the levels for both testosterone and FSH return to normal.
¹⁰

There is more to neurochemistry than neurotransmitters and hormones, however. Another group of Italian neuroscientists looked at the levels of neurotrophins circulating in the blood in those newly in love. Neurotrophins, also called growth factors, are simple proteins involved in synaptic plasticity, or the ability of the connections between neurons to change. Some neuroscientists fondly refer to them as “brain fertilizer” because these proteins help neurons to develop, specialize, grow larger, and live longer. They are also implicated in strengthening neurons to promote learning and memory processes. As described, the brain goes through a lot of changes when you fall in love: it focuses your attention on your intended, increases your good feelings and energy, and makes you a bit obsessive. If that love is returned, it may lead to a lasting bond. Those are some pretty significant changes involving many different brain areas and neurochemicals.
Synaptic plasticity is required to make those changes happen. Without it, and the neurotrophins that facilitate it, our brains would remain forever unchanged, unable to learn or grow.

Considering that learning and memory-related changes in the brain have been linked to increased levels of neurotrophins, Enzo Emanuele, a molecular biologist, wondered if love—which itself involves quite a bit of learning, memory, and brain changes—would show the same kind of pattern. He and his colleagues measured levels of four different neurotrophins in individuals who were passionately in love, single folks, and those in long-term relationships who no longer felt all that passionate about their partner. The group found that one factor, nerve growth factor (NGF), was significantly higher in those who were romantically afflicted. Furthermore the level of NGF was positively correlated with the intensity of love, as measured by a standardized scale: the more in love a participant reported to be, the higher the level of NGF. As in the hormone study, Emanuele retested participants who remained in their relationship twelve to twenty-four months later. Just as was observed in the hormone study, time was all it took for NGF levels to revert back to normal, the same levels seen in the two control groups.
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It is clear that something is going on in the early stages of love, and NGF may have a role in modulating other brain chemicals, mediating some of the brain and behavioral changes we see in new love.
¹²
The truth is, however, that we just don’t know what exactly the NGF might be “fertilizing,” or how it relates to the feelings and behaviors of love.

A Matter of Reception

It is often said that it is better to give than to receive. But giving and receiving are equally important when you’re talking about synapses and neurotransmission. No discussion of love-related neurochemicals is complete without a quick look at their receptors. For any neurotransmitter—any neurochemical, actually—there may be a handful of receptor types that result in different cell actions. One kind of molecule can often also pair up with another chemical’s primary receptor. It is not enough to have a certain level of a particular neurochemical; you must have the right kind of receptors
available, in the appropriate numbers, for it to be taken up by a receiving cell and do its thing. Currently researchers are studying a variety of different receptors related to all these neurochemicals, particularly in the study of monogamy. Different receptors, including a variety of vasopressin and dopamine receptors, have something to say about the strength and longevity of a given pair-bond. I will talk more about some of these specific receptors and their roles in the following chapters.

It’s All about Chemistry

There are a few advice books out there claiming that lasting love is all about proper brain chemistry. To be able to connect with the right person, you need the “right” level of testosterone or oxytocin. Just follow these rules, change your diet, and you can restore your body’s natural balance—or, if that is too much trouble, simply buy a line of related supplements from the author’s online store for optimal love neurochemistry.
¹³
While it is clear that a balanced diet and regular exercise are important to good health, including brain health, there is no evidence of a single
right
chemical balance in the brain. There are kinks to neurotransmitter systems that may lead to disorders like depression, OCD, and ADHD, but in so-called normal populations there is incredible variability in these systems. Even free of disorders, our brains and their innate neurochemistry remain our own, as quirky and unique as any of our other traits and features. Current neuroscience studies offer no indication that love requires a specific level of any one neurochemical or any combination of them.

All these brain chemicals—dopamine, oxytocin, vasopressin, serotonin, and others—are mixed up in the cocktail we call love. Shake it up and—voil à —we see a variety of different brain areas light up as well as a continuum of love-related behaviors. As any good mixologist will tell you, no matter how skilled you are, and no matter the quality of your tools or ingredients, no two cocktails will ever turn out exactly the same. Some bartenders spend years trying to re-create that one perfect drink. But they try in vain.

Alas, you find the same phenomenon in the brain. No two people are going to have exactly the same
brain chemistry. Even with the same partner, no two people will have identical experiences in love. So while neuroscientists are gaining ground in how these various neurotransmitters and chemicals mix together to create complex behaviors, including that four-letter-word that begins with
l,
there is still plenty of ground to cover.

Chapter 4

Epigenetics

(or It Is All My Mother’s Fault)

When I told my mother
I was subtitling a chapter “It Is All My Mother’s Fault,” she laughed and said, “It’s the cheeseburgers!” This is an old family joke. While she was pregnant with me, the only thing my mother could handle was cheeseburgers from a popular fast-food chain. Having just moved to the greater Chicago-land area, she and my father ate most meals out while they waited for their new house to be finished. Each night my mother sat stoically, trying not to retch, through whatever fabulous dinner my father ordered at nice restaurants across the city. But invariably, no matter how hard she tried, she still ended up waiting for him in the ladies’ room or in the car because she was so put off by the food. As soon as he paid the bill, my mother demanded to be taken to said fast-food chain’s drive-thru window. There she would order and then gobble up two or even three cheeseburgers. They were the only thing that appealed to her—and the only thing she could keep down. Ever since, any bad behavior on my part, any lip or misdeed, has been explained away later with the simple sentence, “It’s the cheeseburgers!” (Of course, my successes are often described thus too.)

Little did we know that scientists were discovering that the food moms (and perhaps dads too) eat while babies are in utero can actually make changes to those babies’ genomes—at least, to the way individual genes may be expressed in the body. And the way parents behave after those babies are born can also have profound effects on gene expression. The sum of these behaviors can affect love and parenting style over their
offspring’s entire life span.

Behold the power of the cheeseburgers! They may very well have changed the way I have grown, the way I eat as an adult, the way I love, and even the way I parent. Who knew?

Genes and Behavior

The idea that genes are altered by the environment is counterintuitive at best. Ever since that little double helix called DNA was discovered, we have been taught that our genes are our destiny, inviolate and unbending. Our individual differences in body type, personality, intelligence, behavior, and everything else could all be accounted for by the mix of various genes we received from our parents—but the individual genes themselves remained virtually the same. Sure, evolution may curve a beak or web some toes or make other tweaks here and there, but those mutations were slow in coming, occurring over millions and millions of years. Direct damage to genes, through disease or environmental mishap, might also knock a few nucleotides out of the mix or cause repetition of certain sequences—but again, this was the exception to the rule of fixed genes. And with the start of the Human Genome Project in 1990, it seemed certain we’d soon have the key, in the form of a handy-dandy genomic map, to understanding both behavior and disease. The consistent message from the scientific community was that our DNA was the great decider, directing growth, development, disease, and ultimately behavior. Once we had mapped the human genome, we’d have the primer to help us understand it all.

There are a few problems with this idea of genetic determinism. One of the biggest? Monozygotic (identical) twins. Have you noticed that sometimes these folks aren’t quite so identical? There is often some unique physical trait, a well-placed mole or perhaps a slightly different hairline, to help others tell them apart physically. More important, one of the pair may develop a disorder like asthma or schizophrenia, while the other remains untouched by the disease. And in terms of personality, no matter how close a pair of twins may be, they have their own distinct character. It is astonishing to think that these differences can occur even when you have
virtually identical genomes. How does that work exactly?

It should also be mentioned that genetic studies in the social behavior realm haven’t been quite as satisfying as some had hoped. Twin studies have looked for genes underlying traits like altruism, trust, and fidelity, but they have been unable to pinpoint the exact gene, or genes, involved in those qualities.
¹
What those studies have been able to offer is a basic estimate of heritability. Although that is helpful, it’s not all that specific.

In the past decade there has been a rise in genome-wide association studies, in which researchers compare the genetic idiosyncrasies of thousands of individuals correlated with a particular behavior (usually using survey data). But again, except in rare disorders, most behaviors, like diseases, involve multiple genes. Scientists using these methods can assess probabilities but offer no definite answers regarding an individual gene’s role in something as complex as love.

We often talk about genes as if they are little gods, directing all manner of disease and behavior, especially when it comes to evolution. You’ll even hear some researchers talking about what genes
want
. They want to propagate themselves, to select for the best traits, to endure, and so on. In truth genes are simply little chains of nucleotides that offer cells an instruction manual on the production of small protein molecules. They have no free will, no grand plan for you or the universe. They are simple biological machinery that help cells do their thing.

Though these proteins are critical to brain function, that Demolition Derby we call synaptic activity, they do not act in a vacuum. It is often said the brain is behavior and that the brain is built on genes. But there is no behavior without a stimulus of sorts to prompt it. Clearly there is a crucial interaction here: the biological products of our genes and our environment mix together to result in a particular behavior. As they say, context is everything.