Woman: An Intimate Geography (46 page)

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Authors: Natalie Angier

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BOOK: Woman: An Intimate Geography
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to remember the concept of biofeedback: behaviors and emotions can change the hormonal milieu and the connections between neurons. The brain is pliant. Synapses linking one brain cell to another arise and die and arise again.
For an example of neural and hormonal plasticity, few organisms can match
Haplochromis burtoni
, a cichlid fish found in Africa's Lake Tanganyika. Among this species, only one or a few males in a particular locus of the lake are dominant at any given time. The alpha males are brilliantly colored, nautical neon, while the females and the subordinate males are the shade of sand. Only alpha males have working gonads, and only alpha males can breed, and they are under constant threat of predation, through the attractiveness of their scales, and of usurpation by other males. When a dominant male is forced from his position of power by another, stronger fish, his brain begins to change, quickly and dramatically. The neurons of his hypothalamic pulse generator, which control his gonads and his semen production, shrink down and disengage their synapses. Without the appropriate cues from the brain, his testes shrink as well, and along with the testes the fish loses his primary source of testosterone. He loses his bright coloration and turns dun. He stops devoting his energies to the aggressive patrolling of his territory and becomes low-key, remaining hidden as much as possible. He is not ashamed; he is sensible. He has no testes and no testosterone, so he can't make sperm and he can't mate; and if he can't mate, he might as well retreat until a new opportunity at dominance arises. If his usurper dies or is eaten, the dun fish will have a chance to compete once again for a colorful life, against other drab, agonadal aspirants, and if he wins the contest, his hypothalamus will inflate again, and so will his testes, his testosterone output, and his fecundity, and his scales will turn brilliant, iridescent, arrogant.
The cichlid fish exemplifies how a behavior, or, more precisely, an assessment of reality, can recondition the entire body, from brain to gonads. The behavior is the loss of a fight. The brain reacts first. Somehow the sense of loss induces neural retrenchment, the dwindling of the pulse generator of the hypothalamus. It is not a drop in testosterone that causes the cichlid's brain to change; his neural atrophy precedes any measurable drop in the hormone. Only subsequently, when his gonads have begun to shrivel, does the fish's hormonal content

 

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change significantly. Testosterone in this species is less an actor than a reactor. A drop in the hormone may facilitate or encourage cryptic behavior, but it doesn't
cause
it. In the wake of defeat, the intertwined systems of the brain, gonads, and hormones together effect the most sensible strategy for the cichlid to follow wait and see and enjoy your vacation.
The moral of our small fish story is that the arrow does not point unidirectionally from hormone to behavior, or from neural circuitry A to outcome B. Instead the arrow is like a panel by M. C. Escher, the arrow turning to bird to human to interstitial space and back to arrow. The brain is never fixed. It is a moving target. Your hormones don't make you do anything. Habit and circumstance can have a more profound effect on behavior than anything hormonal. A person who is accustomed to deference will be obeyed into old age, whatever her or his estrogen or testosterone or androstenedione levels may be doing or failing to do. A tomcat that sprayed your house with territorial and reproductive resolve before being neutered may well continue spraying when his testicles are gone. He has learned how to do it, and though the impetus to start spraying may have come with a pubertal surge in testosterone, he no longer needs the hormone to know (as cats know, for they are infinitely wise) that a tomcat must leave a spackle of pong wherever he goes.
The brain is a moving target, and so too is our understanding of its circuitry of aggression. Aggression researchers categorize aggression. They speak of predatory offensive aggression, competitive aggression (also called intermale aggression), fear-induced aggression, irritable aggression, maternal-protective aggression, and sex-related aggression. But don't mistake the existence of categories for consensus. Researchers often disagree, irritably, on the definition of aggression, and on the validity of tests for aggression. A classic test is the intruder paradigm. If you put a mouse into a rat's cage and the rat attacks the mouse and kills it in, say, three minutes, and another rat takes thirty minutes before it kills the mouse, you could conclude that Rat the First is far more aggressive than Rat the Second. But many variables can affect a rat's propensity to strike, including its intelligence, degree of hunger, and mood, not to mention the craftiness and strength of the mouse with which it is presented. In any event, the assay is artificial: in nature, rats

 

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and mice almost never interact, and no mouse is stupid enough to enter a rat's quarters voluntarily.
Just as there is no single ''hormone of aggression," so there is no one seat of aggression in the brain, no discrete place that controls or participates in aggressive feelings or actions. A recent text on neuropsychiatry by Jeffrey L. Saver and his colleagues links thirty-eight different parts of the brain to various behaviors that can be called aggressive. If the cortical tissue around a cat's hypothalamus is first stripped away and a rear portion of the hypothalamus is stimulated with an electric current, the cat will automatically assume the familiar posture of cat rage: hissing, raising its fur, extending its claws, and dilating its pupils. Thus the surrounding cortex is assumed to inhibit aggression, the hypothalamus to foster it, at least in the cat. If you excise a rhesus monkey's amygdala, usually the monkey will become tame and placid. But not always: monkeys that were submissive before the removal of their amygdala often become aggressive afterward. The amygdala is thought to play a role in learning and memory. So maybe what we are seeing in this experiment is that without it, the aggressive monkeys forget to be aggressive and the meek monkeys forget to be good.
Human patients suffering from a variety of head injuries and brain diseases have displayed aggressive, impulsive, violent behaviors, but never neatly, never in a sufficiently localized manner to allow scientists to say, Here is the primary pathway of irritable aggression, or maternal aggression. David Bear, a psychiatrist, tells the story of Rebecca, who as a ten-year-old girl lost consciousness after a head injury. Four years later, she began experiencing seizures, blackouts, and episodes of déjà vu. She turned irritable and hypergraphic, writing lengthy poems and philosophic musings. Electroencephalograms revealed abnormal spiking of her right temporal lobe. At age fifteen she started traveling long distances from home, speaking in a harsh, masculine voice, and becoming violent, often without being aware of her rages. On one occasion she woke up on a grassy knoll with a bloody stick in her hand, next to the unconscious body of a male stranger. Another time, during a therapy session, she abruptly attacked her doctor, holding a knife to her throat for three hours. Later, when Rebecca realized what she had done, she felt such profound remorse that she gave the psychiatrist a vial of her own blood in recompense. In the wake of her temporal-lobe injury, Rebecca

 

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turned aggressive, yes, but at the same time her emotional tone deepened; she felt driven to write, to wander, to find control, to lose control. She became a small, disorganized echo of Hildegarde von Bingen, the great twelfth-century nun, composer, poet, and visionary, who herself had migrainous auras and hallucinations.
When the brain becomes unfamiliar to itself, it often descends into a more primitive, less restrained posture, like a hissing, piloerecting cat. A woman who had her anterior commissure transected in an effort to control her epileptic seizures had difficulty afterward performing her daily ablutions or getting dressed, because her left and right arms would start physically abusing each other. The anterior commissure is a bundle of nerve fibers that allows the two hemispheres of the brain to communicate. Without the cord, each hemisphere was left adrift and fearful, seeing enemies everywhere, including in the arm controlled by the opposite, estranged side of the brain. But is this an expression of the aggressive brain or of the defensive brain? Or of involuted terror, the injured bird flapping its wings desperately, seeking to return to the homeostasis of flight?
The brain is said to be female by default and to be masculinized through exposure to androgens, and it is said that androgens stimulate or mediate or at least sympathize with aggressive behavior. Yet by some neural models, aggression itself is a kind of default humor, the 4/4 tempo to which the brain returns harmoniously; and so the human brain is wrapped with many layers of inhibitory duct tape to repress it and make it less aggressive. In 1848, Phineas Gage, a twenty-five-year-old foreman for a railroad company, suffered a spectacular injury. A metal tamping rod exploded from beneath his hands and shot up through his left eye and out through the top of his skull. His eye was destroyed, but otherwise he seemed surprisingly fine. He was able to talk. He was able to walk with the help of his men, who took him to a nearby tavern. Gage soon recovered from the accident, but he never recovered the Phineas that was expected of him. He became a different man to others, if not to himself. Before, he had been intelligent, hardworking, abstemious, churchgoing. Afterward, he was intelligent, impulsive, and profane. He cursed at his superiors. He cursed people who tried to keep him from fulfilling his fleeting desires. He cursed himself for abandoning plans to live his fantasies. He couldn't keep a

 

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job or a promise. "He was no longer Gage," John Harlow, his doctor, wrote. Using brain imaging technology and computerized renderings of Gage's skull, scientists recently have reconstructed his brain injury, pinpointing the left orbitomedial frontal lobe as the site of greatest damage. They have suggested that herein lies a locus of impulse control the brain's temperate zone, as it were, or its moral center, as the scientists have suggested. But there are other loci of restraint, in other lobes. Many mental illnesses manifest themselves as derangements of control, a de-domestication of the mind. Schizophrenia, manic-depression, posttraumatic stress disorder, phobias in all cases, patients can lash out, bark, yodel, attack, catabolize. My ancestor Silas Angier fought in the Revolutionary War with a regiment from New Hampshire. Like his fellow New Englander Phineas Gage, he was hardworking, ambitious, and self-righteous, a prominent citizen in the obscure town of Fitzwilliam. Toward the end of the eighteenth century, though, Silas had a bloody encounter with a group of Indians and received a blow to the head. He was never the same again. He turned moody and surly. He stopped caring about his reputation. He stopped going to church. He became agoraphobic. Silas died in October of 1808, three days shy of turning seventy-one, in poverty.
We don't understand the endocrinology of aggression, or the anatomy of aggression, or the neurochemistry of aggression. Recently the neurotransmitter serotonin has risen to the fore of aggression research. You think of serotonin and you probably think of Prozac, Zoloft, and the other semihappy pills that have been among the most financially successful drugs of all time. The simple model posits that being "low" in serotonin puts you at risk of aggressive, impulsive, ugly behavior. Mihaly Arató, of McMaster University, has called serotonin the "civilizing" neurotransmitter. The same model also posits that being "low" in serotonin puts you at risk of depression. Depression is often considered a woman's disease, because women suffer from it at two to three times the rate of men (although men are catching up, according to recent international surveys). Aggression and depression sound like two different, even polarized phenomena, but they're not. Depression is aggression turned inward, directed against the self, or the imagined, threatening self. A seriously depressed person may look anesthetized to an observer, but the depressed person is never anesthetized to herself. She may wish

 

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to be, and she may seek to be with chemical aid, but she cannot truly placate her sneering, jabbering, nested aggressor. William Styron described the violence of depression, calling it the true "brainstorm" and a "gray drizzle of unrelenting horror," beneath which the sufferer becomes an old, mad, powerless King Lear. Thus, to compare aggression and depression is a logical step, and if serotonin is implicated in both, that too sounds logical.
But we are far from understanding what or how or where serotonin comes into the landscape of the aggressor or the ingressor. Like steroid hormones, serotonin is an ancient molecule. Lobsters have it, and they respond to it behaviorally, though not in the way we'd think if we simply equate "low" serotonin with aggression. An injection of serotonin will cause a lobster to assume a fighting stance, muscles extended, claws open. In mammals, serotonin's role is less stereotyped and more species-specific. Domesticated silver foxes that tolerate human contact have higher concentrations of serotonin in their midbrain and hypothalamus than silver foxes that bite and snarl at their keepers do. Rhesus monkeys with high serotonin blood counts tend to be socially dominant, while those with very low serotonin levels tend to be aggressive, socially deviant the sort of monkeys you don't want in your barrel. For other species of monkey, though, those serotonin correlations don't hold.
In people, serotonin's influence is even more confusing. The brains of successful suicide victims are in some cases low in serotonin and in other cases not. Scientists have looked at the metabolites of serotonin in the cerebrospinal fluid of violent criminals with similarly inconsistent results. As a group, pyromaniacs and those who have committed impulsive manslaughter show reduced levels of serotonin metabolites, but rapists and wife beaters do not. Nor have studies of depressed patients been able to detect a decrement in serotonin metabolism, as much as we might want this as blood proof of depression's organic origins.
Whatever is going on with serotonin, it is polyphony. There are at least sixteen types of serotonin receptors, distinct proteins capable of responding in distinct ways to serotonin. To what end, though? We don't know. Do neurons like the taste of serotonin? Do they covet it? We don't know. The drugs called serotonin reuptake inhibitors, of which Prozac and Zoloft are examples, appear to work by discouraging the

 

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