We Are Our Brains (15 page)

The PFC plays a central role in regulating other brain areas and is responsible, among other things, for the control of our impulses, complex actions, planning, and organization. It doesn't fully mature until a person is in his or her twenties. According to the neuropsychologist Jelle Jolles, this explains why a recent restructuring of the Dutch secondary school system that focused on independent study
is flawed. When your PFC hasn't matured, you're not very good at organizing your work and making independent choices. Functional scans also show clear differences between the brains of adolescents and those of adults. Adults distribute assignments across different brain areas. Adolescent PFCs can sometimes function at an adult level but need to work much harder to do so, as they fail to outsource tasks to other brain areas. As a result, a teenager's PFC reaches the ceiling of its capacity earlier, and distractions can undermine the performance of assigned tasks.

The regulation of day-night rhythms is also influenced by sex hormones. That might explain why it's so hard to get adolescents out of bed in the morning and into it at night. Should we force them to get up early or adapt school hours to their biological clocks?

A lot of drinking goes on in puberty: At the age of fifteen, 52 percent of boys and 46 percent of girls in the Netherlands drink at least five units of alcohol an evening on the weekend, and children of that age regularly end up in a coma in intensive care. The practice of “pre-gaming” before going to parties is now quite common. Alcohol abuse makes the brain shrink, causing permanent damage. In Europe, around fifty-five thousand youngsters die annually of alcohol poisoning or in traffic accidents in which alcohol was involved.

The sudden surge of sex hormones during puberty causes not only sexual awakening but also typical male aggression and risk-seeking behavior. That explains why the incidence of unrestrained, antisocial, aggressive, and delinquent behavior increases during puberty. A survey in the Netherlands showed that one in three children between the ages of ten and seventeen commits a crime, ranging from theft and breaking and entering to vandalism and crimes of violence. After the age of seventeen, young people commit fewer crimes. It seems logical to assume that this curve reflects the gradual development of the PFC, which inhibits impulsiveness and promotes moral behavior. Parents can take comfort in the thought that puberty is a finite process. Teachers, on the other hand, must sometimes despair. As fast as they mold adolescents and launch them into
society, a fresh crop of impulsive youngsters enters the school gates. For teachers the process is never over.

A great many brain processes are involved in various stages of our love lives, including falling in love, sexual arousal, attachment leading
to long-term partner bonding, and maternal and paternal behavior (see
chapter 1
). Although it wasn't Mother Nature's “intention,” we see on a daily basis that these stages can perfectly well exist independently of one another, and I will therefore look at them separately.

FIGURE 15.
The prefrontal cortex (PFC) as seen from the side (external view at top, cross section at bottom).

No one who can still remember the suddenness and intensity of falling passionately in love will classify partner choice as a free choice or even a well-considered decision. Love at first sight just happens—it is pure biology—along with all the euphoria and severe physical reactions that ensue, like a beating heart; perspiration and insomnia; emotional dependency; strongly focused attention; an obsessive, possessive, and protective attitude toward the partner; and a feeling of heightened energy. Plato (427–347
B.C.
) was equally convinced of the autonomy of this process. He regarded the sexual impulse as a fourth species of soul, located below the navel, describing it as “rebellious and masterful, like an animal disobedient to reason.”

For people all over the world, falling in love tends to be the basis for pair forming. You might think that where something as important as choosing someone to start a family with is concerned, our cerebral cortex would select the right person on a fully conscious basis. But no, during severe infatuation, when all of our attention and energy is focused on that one other person, it's the areas down at the base of the brain, in structures that steer unconscious processes, that call the shots.

Brain scans of people who had just fallen deeply in love and who were shown a photograph of their significant other showed activity exclusively in brain structures below the cerebral cortex. Their reward circuitry was particularly active. This part of the brain focuses on obtaining a reward (in this case, for finding a partner) in the form of a pleasurable sensation, which is transmitted by the chemical messenger dopamine (
fig. 16
). The reward system isn't involved just in matters of the heart but in everything that we find pleasant. It's also associated with addiction, which explains why people experience severe withdrawal symptoms when a love affair ends. Scans show this system to be primarily activated on the right side of the
brain, in proportion to the attractiveness of the face in the photo and the intensity of the romantic passion.

People who are in love also have raised levels of the stress hormone cortisol. Being in love is a stressful situation, and the body responds by producing more of this hormone. The level of testosterone (also produced by the activated adrenal gland) increases in women who are in love, while in men, cortisol reduces the testicular production of testosterone.

It's only when love has persisted for a certain length of time that the prefrontal cortex, the front part of the brain involved in planning, deliberation, and assessment, becomes involved. If stable pair formation ensues, the activity in the stress axis dies down and testosterone levels return to normal. The processing of sensory information in the cerebral cortex has of course played a role during that exciting period—we have, after all, seen, smelt, and touched the person we love. But this isn't the same thing as making a conscious
choice for that particular person. Whether they are “Mr. (or Ms.) Right” is determined by our ancient reward circuitry, which thus links reproduction to the “right” partner—or at least the right partner in that moment. Only when the most intense period of infatuation has passed does the cerebral cortex take over. So if your son or daughter suddenly falls for the wrong person, it's no good reproaching them that they should have used their brains. They did, in fact, do so, but those parts of the cerebral cortex (such as the PFC) that could have come to a different decision after a balanced, conscious judgment unfortunately only kick in when it's too late.

FIGURE 16.
The dopaminergic reward system, originating in the cell bodies in the ventral tegmental area (1), whose fibers extend into regions including the ventral striatum (ventral pallidum/nucleus accumbens [2]), the caudate nucleus (3), and the prefrontal cortex (4).

Our gender identity (the feeling of being male or female) and our sexual orientation (whether we're heterosexual, homosexual, or bisexual) is fixed in our brains while we're still in the womb (see
chapter 3
). The circuits for our sexual behavior, which are established early on in development, are subsequently activated during puberty. An extreme form of gender identity disorder is transsexuality (see
chapter 3
). Transsexuals are convinced at a very early stage, often from the age of five, that they have been born with the wrong body, and they are desperate to change their sex. The theory that an atypical sexual differentiation takes place at an early stage of their development has been confirmed by our discovery of female structures in male transsexual brains and vice versa. However, before treating transsexuals, it's important to rule out the possibility that their desire for a sex change isn't part of a psychosis caused by schizophrenia, a bipolar disorder, or a serious personality disorder. In the case of changes in sexual orientation, disorders of the brain also need to be
ruled out. A shift from adult heterosexuality to homosexuality or pedophilia is sometimes seen in patients with brain tumors or with brain disorders like damage to the temporal lobe that cause uninhibited sexual behavior.

Since there's a time and place for everything, many areas of the brain are constantly busy inhibiting our sexual urges. This is usually effective for around twenty-three hours a day. Sexual disinhibition, or hypersexuality, is seen in patients who have suffered damage to such inhibitory brain areas. This type of brain damage can also cause paraphilia (atypical sexual arousal, for example in response to inanimate objects), sadomasochism, or pedophilia. Some forms of epilepsy are treated by surgically removing part of the temporal lobe, and operations of this kind occasionally result in a type of hypersexuality known as Klüver-Bucy syndrome. One man who had undergone this operation wanted his wife to have sex with him five or six times a day, in between which he masturbated. The amygdala, an almond-shaped structure located in the front part of the temporal lobe, regulates aggression and inhibits sexual behavior, among other things. Sometimes, in order to treat unmanageable forms of aggression, the amygdala is surgically lesioned, which occasionally also results in patients developing Klüver-Bucy syndrome.

Electrically stimulating the amygdala, on the other hand, has been shown to induce pleasant sexual sensations. In other brain structures, too, this method of stimulation can generate sexual behavior. Patients with an electrode inserted into the septum (
fig. 26
) were able to induce orgasms in themselves; some even developed a compulsion to masturbate. Patients whose septum has been accidentally perforated by the tip of a plastic tube inserted to drain cerebrospinal fluid to the abdominal cavity (a ventriculoperitoneal shunt) sometimes experience heightened sexual urges, while, conversely, damage to the septum has also been shown to cause impotence. Such cases help shed light on the brain structures that inhibit our sexual impulses and enable us at least to keep up the appearance of being decent members of society.

Orgasms Can Be Seen in the Brain

Sex starts and ends in the brain. Many cerebral systems keep our sexual behavior constantly in check, but when we fall in love, inhibition flies out of the window. Our brain structures spring into action, sending messages via the spinal cord and the autonomic nervous system preparing our sex organs for that one true purpose of existence: the fertilization of an egg. To encourage us to truly commit to that objective, the brain provides orgasm as a reward. Impulses caused by the stimulation of our sex organs travel via the spinal cord to the brain, arriving at the thalamus (
fig. 2
), the central structure for all erotic sensory information. These then travel on to the ventral tegmental area (
fig. 16
), with its dopamine-delivering reward circuitry, and the hypothalamus (
fig. 18
). If all of these impulses lead to orgasm, we're simultaneously rewarded by the release of dopamine into the nucleus accumbens (
fig. 16
) and of the “love hormone” oxytocin in the hypothalamus (
fig. 5
), which increases social interaction between partners and promotes the release of opiates in the brain. All of these substances are so addictive that the number of people on earth has now swelled to seven billion.

People differ in all kinds of ways, including the extent to which they are interested in sex. DNA polymorphisms, tiny differences in the gene for the protein that receives dopamine's chemical message (the dopamine D4 receptor), are correlated to the degree of sexual desire, sexual arousal, and sexual activity itself. An overactive dopamine system can also cause problems. People with Parkinson's disease have a dopamine shortage; they are treated with L-dopa, which is transformed into dopamine in the brain. A possible side effect of this treatment is hypersexuality. One of the surgical methods used to treat Parkinson's involves implanting a depth electrode in the brain, in the subthalamic nucleus (
fig. 23
), in order to reduce tremor. However,
stimulus of this kind can occasionally cause patients to develop hypersexuality, with or without mania.