Making the Connection: Strategies to Build Effective Personal Relationships (Collection) (63 page)

Having observed this behavioral result, Meaney and his colleagues looked for differences in the brains of the two groups of pups. They found that the highly licked animals had a more active form of the gene that makes the glucocorticoid receptor (GR), a protein that responds to glucocorticoid hormones. This change, which was observed in neurons in brain circuits that control emotions, was already detectable in the pups’ brains during the first week of nursing and was maintained throughout their lives.

To find out how this came about, the researchers searched for modifications in the promoter part of the GR gene, which regulates the gene’s activity. It is known that promoters can be modified by a natural biochemical reaction, called an epigenetic change (from the Greek epi, which means “over” or “above”), which adds or removes a tiny methyl group at a precise point in their DNA, and that an epigenetic change may modify the promoter’s effectiveness and alter the activity of the gene. The researchers discovered that the promoter of the GR gene was less methylated in the highly licked animals and that this change of their brain DNA, which was caused by their mothering, led to an increase in the manufacture of the gene’s protein product, the glucocorticoid receptor.
³²

Furthermore, the behaviorally induced change in the methylation of the gene’s promoter was maintained in the
highly licked animals as they grew up. So, too, was the activity of the GR gene. This suggested that the enduring epigenetic change in the DNA of these animals, and the resultant increase in glucocorticoid receptors, had shifted the settings of a brain circuit that controls the stress response. The result was a sustained effect on their personalities.
³³

The research with high-licking mothers has attracted a lot of attention because it has something for everyone. Geneticists like it because it demonstrates the importance of an environmentally induced chemical modification of a gene. Psychologists like it because it shows that behavior can affect genes as dramatically as genes can affect behavior. Neuroscientists like it because it adds to their understanding of the ways that experience can produce a sustained change in brain circuits. And, to all of them, a major implication of these studies is that experiences, especially those in early life,
³⁴
can produce epigenetic modifications of DNA that have enduring effects on personality.

Such environmentally induced epigenetic changes keep accumulating as we grow up. One way we know this is from studies of identical twins. Derived from a single fertilized egg, these twins start out with identical DNA. Nevertheless, the methylation pattern of their DNA becomes progressively different as the twins grow older.
³⁵
These epigenetic differences in the DNA of identical twins are believed to be due, in part, to the many differences in the environments the two twins grew up in. Although the functional significance of these epigenetic differences is not yet known, it is reasonable to assume that they give rise to some of the observable
differences between identical twins, including differences in their personalities.
³⁶

Adolescent Remodeling

Although a great deal of brain development takes place in fetal life and childhood, extensive remodeling also occurs in our teens. Some of this structural remodeling is initiated by a few thousand specialized neurons in the hypothalamus that trigger the hormonal changes of puberty. These neurons make a small protein, gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to activate the ovaries or testes to secrete estrogen in girls and testosterone in boys.
³⁷
Bursts of these hormones then modify, enlarge, and activate the brain circuits for sexual behavior that were first built in the fetus.
³⁸

The sex hormones also do much more. By activating neurons that have receptors for estrogen or testosterone, they change the activity and settings of many other brain circuits. This gives rise to behavioral changes that are typical of adolescence, such as increased sexual interest, risk taking, impulsivity, and social awareness.
³⁹

But sex hormones are only one factor in the brain remodeling and behavioral changes of adolescence. Many other sex-specific changes in brain gene expression don’t depend on these hormones. Both the hormone-induced and the hormone-independent processes lead to enduring modifications in brain circuits, some of which distinguish male from female brains.
⁴⁰

As in other periods of brain development, adolescence provides opportunities for genetic variations to make themselves felt. For example, some gene variants that influence cognitive abilities may not exert their full effects until the mid-teens. We know this, in part, from studies of the IQs of adopted children. These studies show that their IQs become progressively more like those of their biological parents during adolescence, as the influence of gene variants that influence cognitive abilities becomes more apparent.
⁴¹
This increasing effect of the gene variants that influence cognitive abilities was confirmed in a study of 11,000 pairs of identical or fraternal twins. The researchers found that the heritability of general cognitive abilities increased from 41% at age 7, to 55% at age 12, and to 66% at age 17.
⁴²

Adolescent brain remodeling is not apparent solely from the behavioral changes of the teen years. It has also been observed directly by magnetic resonance imaging (MRI) of brain structures at various stages of development.
⁴³
The most extensively studied anatomical changes are those in the front part of the brain, especially the prefrontal cortex, which sits behind the forehead. As adolescence progresses, changes take place in the structure of regions of prefrontal cortex and their connections to brain regions such as the amygdala, which regulates emotional expression.

Changes in the connectivity and organization of brain networks during adolescence and early adulthood has not been observed just by looking at static brain structure. Functional magnetic resonance imaging (fMRI), which measures the activity of brain circuits during the performance of
mental tasks, has also been used. These studies of mental activity reveal substantial changes in the functional connectivity of the brain in the progression from adolescence to adulthood.
⁴⁴

The long critical period of adolescence is also open to environmental influences. While the brain is actively rewiring, life goes on, and peers play extremely important roles in transmitting values and social skills.
⁴⁵
This openness to peer influence is of particular interest to parents, educators, and clinicians, who would like to prevent the many troublesome personality patterns that start showing up at this stage of life.
⁴⁶

Closing Some Windows in the Brain and the Environment

When is brain development completed? MRI studies of individuals show that brain structure stabilizes at around age 25.
⁴⁷
Although a little more myelination may continue for at least another decade,
⁴⁸
changes that show up on brain scans after age 40 are generally signs of wear and tear rather than additional developmental remodeling. Furthermore, studies of the integrated activity of brain regions that is measured by functional MRI show that mature brain networks are also well established by young adulthood.
⁴⁹

This doesn’t mean that the adult brain has become fixed and immutable. One of its most important functions is to keep learning and storing new information by making microscopic changes in the structure and function of synapses.
Nevertheless, young adulthood marks a milestone in brain development, when we have largely built the personal instrument that will continue to guide us for the rest of our lives.

Development of basic personality traits follows a similar trend but lags behind. As anatomical changes in the brain are winding down in our third decade, changes in the Big Five are winding down too. Repeated testing shows considerable stabilization of a person’s Big Five scores by age 20, significantly more stabilization by age 30, and a little more stabilization until about age 50.
⁵⁰

This progressive stabilization is not only due to the closing of windows of brain development. As Roberts and Caspi point out,
⁵¹
it is also due to the increasing constancy of the young adult’s social environment. This is the environment that is populated by the friends, partners, and coworkers whom they have selected—and who have selected them.

The result of selecting a fairly constant social environment during young adulthood is that we subsequently spend most of our time with a limited cast of familiar people. These people provide stability because they keep behaving in ways that
we
have come to expect. They also elicit stability because they keep us behaving in ways that
they
have come to expect. This mutual stabilization of our social environment plays a big part in the creation and maintenance of the two overarching aspects of personality that I now turn to: character and sense of identity.

Part III: Whole Persons, Whole Lives

It matters not how strait the gate,

How charged with punishments the scroll,

I am the master of my fate:

I am the captain of my soul.

—William Ernest Henley,
Invictus

Five. What’s a Good Character?

When Benjamin Franklin was an old man he revealed the secret of his fulfilling life. It was, he said, a technique that he had invented in his twenties to improve his personality.

The personality that Franklin began shaping was already standing on a strong foundation. Ever since childhood he was, according to his
Autobiography,
“the leader among the boys.”
¹
But this same assertiveness cost him dearly by leading his father to withdraw him from the Boston Latin School, where he had been enrolled to prepare him for the clergy. Even though Franklin was at the top of his class and seemed destined for Harvard, then a Puritan finishing school, his father decided that he was too irreverent to be a minister and apprenticed the 12-year-old to his brother, James, a printer.
²

Fortunately the work in the printing shop allowed Franklin to indulge his passion for reading and gave him the opportunity for an ambitious program of self-education. In studying essays from a London periodical he learned to write so well that he was soon publishing satirical pieces in his brother’s newspaper. He was also strong-willed enough to escape from his apprenticeship. At the age of 17 he ran away to Philadelphia with only a few coins in his pocket.

During the next few years Franklin had his share of youthful adventures. But as he settled into young adulthood, he felt the need to take more charge of his life. To this end he decided to curb his passions, break some bad habits, and build up the moral part of his personality, generally called character.

The approach Franklin took to building good character began by identifying its essential ingredients. Franklin was already clear about the character traits that interested him, which he called “the moral virtues.” But when he got down to making a list of them, he ran into the terminological problem that continues to bedevil contemporary discussions of personality because “different writers included more or fewer ideas under the same name.” In Franklin’s case, he decided “for the sake of clearness, to use rather more names, with fewer ideas annexed to each,” and settled on 13 virtues, with brief explanations:

•
Temperance
—Eat not to dullness; drink not to elevation.

•
Silence
—Speak not but what may benefit others or yourself; avoid trifling conversation.

•
Order
—Let all your things have their places; let each part of your business have its time.

•
Resolution
—Resolve to perform what you ought; perform without fail what you resolve.

•
Frugality
—Make no expense but to do good to others or yourself; i.e., waste nothing.

•
Industry
—Lose no time; be always employed in something useful; cut off all unnecessary actions.

•
Sincerity
—Use no hurtful deceit; think innocently and justly, and, if you speak, speak accordingly.

•
Justice
—Wrong none by doing injuries, or omitting the benefits that are your duty.

•
Moderation
—Avoid extremes; forbear resenting injuries so much as you think they deserve.

•
Cleanliness
—Tolerate no uncleanliness in body, clothes, or habitation.

•
Tranquility
—Be not disturbed at trifles, or at accidents common or unavoidable.

•
Chastity
—Rarely use venery but for health or offspring, never to dullness, weakness, or the injury of your own or another’s peace or reputation

•
Humility
—Imitate Jesus and Socrates.