Edited by HENRY REED, Ph.D.
December 02,   2009


Its Origins in Sensation, Stress, and Immunity

(An Excerpt from The Spiritual Anatomy of Emotion*

By Michael A. Jawer)

The peepholes of life. Senses to detect the world. . . . The peepholes begin to open before birth. They are synonymous with life. . . . Throughout our lives, until the peepholes of the senses close, we are sentient beings, sensing the energy and chemicals and objects in our environments. Jillyn Smith, science journalist


We often don't appreciate just how wondrously complex we human beings are, or for that matter, the complexity of our animal friends, who share our planet and participate in life themselves. All of us are sentient: we perceive through our various sensory organs, we feel, and we react. There is great equality in sentience. While the capability of any given sense differs from species to species, the basic capacity to take in environmental information and literally make sense of the world is a trait common to every life-form on Earth.

Thinking, on the other hand, is not so widespread, nor is self-awareness. So many other creatures live their lives on instinct and reflex; for them, thinking is a rudimentary affair. The province of consciousness is rather narrow compared to the spectrum of sentience, which spans the animal kingdom. Sentience, of which feeling is part and parcel, characterizes all those -- humans or animals -- that we take to be individuals.

In the previous chapter, we established sentio, ergo sum (I feel, therefore I am). If this formulation is correct, it can be rephrased "I feel, therefore I am a self." In seeking the origins of selfhood, then, we ought to begin with the sensory foundations of feeling.

It's a common misconception that life begins at birth. While it is not my desire to open up the Pandora's box of precisely when life begins, clearly the human fetus -- and the equivalent forms of other animals -- is functioning well before birth, with sensory organs, circulatory and digestive systems, a nervous system, and other parts of its developing form. The more our technology is able to probe into the origins of individual life, the more we comprehend how extraordinarily complex and awe-inspiring these arrangements are. But how does the self actually emerge? By self, I mean the unique, composite organism that ultimately lives, ventures forth into the world, grows, and learns. The roots of selfhood are as fascinating as any subject we can imagine -- and they begin with that most basic of sensory perceptions, touch.


The sense of touch is the first one to develop. At six months, when the embryo has neither eyes nor ears, its skin is comparatively well formed. If stroked lightly at this age, the embryo will bend away from the source of stimulation. In the womb, enveloped by the mother's amniotic fluid, the skin of the embryo -- and later the fetus -- must "have the capacity to resist the absorption of too much water . . . to respond appropriately to physical, chemical and neural changes, and to changes in temperature."

Skin is basic to our existence: without it, what would enfold us? Not only are we covered by skin, but our skin also turns inward to line such features as the eye, ear, mouth, nose, and anal canal. In that respect, it is the "mother" of each of the other senses. The skin can further be said to represent the organism's external nervous system, since both the skin and the internal nervous system arise from the embryo's surface covering, the ectoderm. While the brain and spinal cord develop from the inward-turned portion of the ectoderm, the rest becomes our hair, teeth, and sensory organs. Ashley Montagu, the late anthropologist and author of a seminal work on touch -- called, appropriately enough, Touching -- observes that "from its earliest differentiation, [the skin] remains in intimate association with the internal or central nervous system." He comments further, "The skin itself does not think, but its sensitivity is so great, combined with its ability to pick up and transmit so extraordinarily wide a variety of signals, and make so wide a range of responses, exceeding that of all other sense organs, that for versatility it must be ranked second only to the brain itself."

Montagu coined the phrase "the mind of the skin," which captures this relationship. His formulation anticipated the term "bodymind," which gained currency in the 1970s and, as we shall see, remains a highly accurate depiction of the interconnectedness of brain and body. As we shall also see, this interconnectedness is mediated by our feelings.

In the typical adult, the surface of the skin has an enormous number of sensory receptors involved in the apprehension of heat, cold, pressure, and pain. A piece of skin the size of a quarter contains more than three million cells, one hundred sweat glands, fifty nerve endings, and three feet of blood vessels. It is estimated that there are some fifty receptors per one hundred square millimeters, giving a total of 640,000 sensory receptors. Interestingly, the skin also conducts electricity. Its sensory receptors are electrically activated when stimulated; this process can be measured in so-called lie detector tests, which, in reality, do not measure a person's truth-telling so much as demonstrate his or her physiological reaction to a given thought, idea, or memory. The amount of electricity typically generated is in the range of 10 - 100 millivolts (a millivolt being one-thousandth of a volt). As they do in other capacities, individuals vary in this one, with certain people appearing to manifest an ability to generate considerably more electrical charge. (This intriguing possibility will be explored in chapter 6.)

As one would expect, the areas of the brain that register and process tactile influences (not only touch per se, but also air movement, changes in pressure and humidity, and other sensations) are correspondingly large. The gross numbers similarly attest to the importance of this sensory organ in our lives. The skin of the average male adult weighs about eight pounds, or roughly six to eight percent of his total body weight.

Here's another yardstick by which to measure the paramount importance of touch in our lives. That yardstick is language. The way we talk to one another is emblematic of how we perceive ourselves in the world. Consider the ubiquity of phrases such as:

Reach out.

Hold on.

Get a grip.

Lean on me.

Let's be in touch.

Don't be so thin-skinned.

He's hard to handle.

She's abrasive.

Our agreement is firm.

I need something tangible.

It pains me to hear you say that.

Don't be so touchy.

Shake it off.

She's tactful.

He's heavy-handed.

Don't you get it?

He's cold.

She's hot.

It just feels right.

To further illustrate the preeminence of touch among our sensory perceptions, consider Helen Keller, who became blind and deaf in infancy but nonetheless led a full and exemplary life. Montagu notes that "a human being can spend his life blind and deaf and completely lacking the senses of smell and taste, but he cannot survive at all without the functions performed by the skin."

Four centuries ago, the philosopher Thomas Hobbes put it well when he said, "The shape and form and space of the outer world of reality, its figures and the background from which they emerge, are gradually built by the infant out of the building blocks of its experience, entering through all its senses, always contingent, correlated, measured, and evaluated by the criterion of touch."

So what is the infant's -- and, going back further, the neonate's -- experience like? A leading researcher, Sibylle Escalona, writes, "the baby's life is a succession of . . . touches, sounds, sights, movements, temperatures, and the like." From a base of such experiences, the infant begins to differentiate itself from the world "out there." The baby reacts, is reacted to, and so on. He or she begins to acquire a sense of himself or herself as someone to whom things happen and who can make things happen. This is the beginning of selfhood. The process is evident in infancy, but has its beginnings in the womb.


Just as touch is the first sense to develop in the individual, it was also, quite probably, the first such capacity to emerge in humankind's evolution. Close on its heels had to have been the sense of smell. Why? Because the oldest form of communication on this Earth is chemical. The chemical senses -- smell and taste -- enable even the most primitive organisms to discriminate self from other and to identify potential food sources, mates, and friends apart from what could be poisonous, unfriendly, or simply irrelevant. Territory, dominance, reproductive status, diet, and health are all conveyed through chemical signals, which are cheap in terms of the energy required to produce them and efficient because of the tremendous effect they can have, even in low concentrations.

One estimate is that more than half a million odors are floating around in the world. Most of these have a biological origin and carry vital information intended for various species. To make sense of them, though, you have to be the right species in the right place at the right time. Dogs, for instance, have a vastly larger olfactory capacity than humans, and they can sniff the breeze or the ground and learn the equivalent of one's morning newspaper. Along with other mammals such as lions and wolves, dogs can track extremely well and are able to identify individual human beings as well as others of their species by chemical signatures.

Other animals get their news in other ways. Snakes and lizards flick their tongues in the air, gathering in wayward molecules and then inserting the tongue into a chemically sensitive structure in the roof of their mouth. Smells emitted when an animal is threatened can also be telling. Antelopes are known to emit a musky smell when disturbed, and frightened house mice leave traces of concern so clearly on the surroundings that these paths of flight are avoided by other mice for up to eight hours. Of course, the aromatic results of an upset skunk will be carried for miles around.

The chemical senses are, along with touch, known as the proximity senses, as contrasted with the distance senses of vision and hearing. The distinction is significant given that the most pleasing and most disgusting sensations we know are registered through touch, smell, and taste. While "we can shut our eyes against a disturbing image, or cover our ears to avoid anything discordant . . . we have to go on breathing." Similarly, we have to go on tasting, lest we die of starvation. And smells carry a particularly intense charge for us, due to the fact that the nose is directly linked via a nerve fiber pathway to that ancient part of our brain, the limbic system. The limbic portion is concerned almost exclusively with the "four Fs": feeding, fornicating, fighting, and fleeing. The rest of the brain evolved from this base. Thus, smells of whatever kind are entwined with our instincts, our appetites, our emotions, our sexual behavior, and our response to stress.

Discriminating odors is quite a complex business: "When we sniff, we inhale odor molecules, which then bind to receptors in the nose. There are at least three thousand molecules that we can distinguish and we have at least one thousand odor receptors in our nose. Different types of odor molecules activate different combinations of receptors, alerting us to what we are smelling." This capacity is evident early on in newborns. At six days old, awake babies can discern the difference between their mothers and strangers. The process began well before that, of course, in utero.

The same can be said for hearing. Between its own heartbeat, its mother's heartbeat, and the rhythm of her breathing, the fetus lives in a fluid world of syncopated sound. It is also well known that the fetus is capable of responding to sounds outside of the mother's body, hence the trend toward playing classical music near pregnant women with the notion that it will enhance the baby's brain development. This idea, while probably misguided, does recognize the relationship between our sensory "peepholes" and the brain's decoding, interpretation, and recall of the information provided by them. Through the brain, raw sensation becomes perceptual.

Critical Junctures in Brain Development

To have perceptions at all -- indeed, to realize that an "I" exists that is something more than the sum total of one's bodily sensations -- a brain is necessary. The brain, of course, does not exist separately and in its own right. Its structure and capacities develop in tandem with sensory input. Activation of the senses stimulates nerve cells (also known as neurons) to grow and interact with one another. And you have a staggering number of neurons! Your brain is made up of one hundred billion of them, each networked with thousands of others. Neurons, though, make up just ten percent of the cells in the brain. The other ninety percent are support cells called glial cells. While their function is not completely understood, one significant aspect of glial cells appears to be insulation of the "conducting cables," or axons, that carry electrochemical impulses between neurons. By surrounding, protecting, and nourishing those transmission pathways, the conglomerations of glial cells help speed messages within the brain.

In its first year after birth, the infant's brain grows more than it ever will again, attaining seventy percent of its final weight. By the end of three years, brain growth is up to ninety percent. This remarkable development is exceeded only by the brain's spectacular growth in utero, when nerve cells are generated at the rate of 250,000 per minute during peak growth. No wonder, then, that the fetal brain is highly susceptible to "environmental influences that may affect its developmental trajectory and, in worst cases, cause structural or functional damage that may not be evident for years to come."

In the earliest phase of the brain's development, nerve cells are restlessly moving around, each heading for its unique location as designated by our genetic blueprint. But, as with blueprints for a house, elements of the final construction may differ from what the plans called for, depending upon the construction materials used, decisions made on site by the builder, the impact of intensive or unanticipated weather conditions, and so on. In the same way, key factors such as the mother's diet, her habits such as smoking or drinking, her feelings about the baby, her stress level, and her general state of health or illness all stand to affect the developing fetus. Hormone levels, the concentration of oxygen in the blood, and the supply of glucose and other nutrients are all avenues by which the fetus can be influenced, for better or for worse. Peter Nathanielsz, a prominent researcher into prenatal development, uses the term "programming" to describe the long-term effects on biological functioning that can be dictated by external influences. He comments, "During fetal and newborn life, there are critical periods in the growth and development of each organ in our bodies. At these critical times, each individual organ is especially sensitive to challenges that have the potential to permanently alter the development of that organ and hence the whole body. . . . In addition, when a critical phase . . . is missed or even significantly delayed for any reason, the next step may be impeded . . . each milestone interacts with the next one. Timing is everything."

Here is an example from the animal kingdom. If newborn female rats are injected with a single dose of male sex hormone on the fifth day of their life, they will never ovulate. Their reproductive brain centers will have been reprogrammed and permanently altered. However, if female rats are injected with the same hormone on the twentieth day of their life or later, they will be completely fertile once they reach puberty. The difference, in this case, is not the foreign hormone but its timing. By the twentieth day, the critical window of vulnerability -- to this substance, at least -- is past. To take another example, the corn lily plant contains a toxin that causes deformities in the fetuses of pregnant sheep. Depending on what day of gestation a sheep ingests the corn lily, a different deformity can occur.

In human beings, a variety of conditions can prompt permanent alterations in the development of the brain and spinal cord. Let us return to the case of nerve cells moving about the brain in its very earliest stage. If, for whatever reason, one set of cells is slow to settle into its particular location -- or, worse, gets into the wrong place -- the whole structure of the brain can be compromised. As Nathanielsz describes it, the birth, connection, and activation of neurons is interlinked. If a cell makes a mistake, gets the wrong information, or doesn't reach its correct location, subsequent activities may not occur or may be carried out incorrectly. What holds true for neurons also holds true for their support system, the glial cells. The glial cells need to be properly developed in order to do their job. Neurons alone do not a brain make.

Stress and Its Effect on the Fetus

The correlation between a mother's health and her baby's functioning is easy to understand given the obvious fact that, during pregnancy, the fetus is locked in a biological embrace with its mother via the placenta, an organ that acts as a lung (transporting oxygen), a gut (transporting food), and a kidney (removing waste). The placenta is a conduit between mother and child, protecting the latter from some harmful compounds, but alas, not all of them.

When we look closely at the function of the placenta, at times when challenges and stresses of various kinds occur to the mother, we find it entirely possible that the mother's response to such challenges may program the developing baby's lifelong capacity to handle stress on its own. Such stress in the mother may also program the child's disposition later in life toward conditions such as depression, chronic fatigue, and alcoholism, not to mention a weakened (or, alternately, hypersensitive) immune system and tendencies toward shyness and sensory defensiveness (a condition characterized by extreme sensitivity to light, color, texture, noise and/or smell).

How can such wide-ranging effects be possible? The culprits are two biological systems that are involved in a person's (in this case, the pregnant mother's) response to stress. The first is the sympathetic nervous system, which links the brain to the other internal organs and regulates essential functions such as breathing, heart rate, and digestion. Normally the functioning of this system is unconscious (e.g., you don't normally realize you're digesting food unless you have gas pains or heartburn). But in a stressful or alarming situation, the system kicks into overdrive, diverting blood from the skin to the muscles for a fight-or-flight reaction, marshaling additional oxygen for respiration, causing your body to sweat so that your insides are kept cool, and reacting in other ways.

The brain trigger for these reactions is a structure called the hypothalamus. While the hypothalamus normally serves to regulate pleasurable functions such as eating, drinking, and sex, in moments of anxiety or threat it stimulates the adrenal glands (located on top of each kidney), causing them to release the hormones noradrenaline and adrenaline. A mildly stressful activity such as public speaking is known to elicit a 50 percent increase in the amount of noradrenaline circulating in the bloodstream and a 100 percent increase in the amount of adrenaline. People who suffer from chronic stress register persistently raised levels of both hormones, along with side effects such as high blood pressure, gastrointestinal problems, high levels of cholesterol in the blood, increased muscle tension, and headaches. (Interestingly, there is evidence suggesting that more noradrenaline is produced in situations where the person can exercise a degree of control over the anxiety-provoking source, whereas uncontrollable fear or angst provokes a greater output of adrenaline.)

The second major player in the mother's stress response is the HPA system, which involves the hypothalamus and the pituitary and adrenal glands (hence HPA). When this system is activated, a similar cascade of changes takes place in the brain and body. The major difference from the action of the sympathetic nervous system is in the duration of the response. Whereas activation of the sympathetic nervous system occurs within seconds of the perceived threat, and its effects subside within an hour or so of that threat's passing, the HPA system takes minutes to get going, and its effects may persist for days, weeks, or longer.

The HPA system's activity begins when the hypothalamus sends a hormone known as corticotropin-releasing hormone (CRH) to the pituitary gland, a pea-sized outgrowth of the brain located just below the hypothalamus. The CRH stimulates the pituitary gland to release a second hormone called adrenocorticotropic hormone (ACTH). This hormone is carried via the bloodstream to the adrenal glands, which, in turn, release a slew of other hormones. The most relevant of these for our discussion is cortisol, a kind of steroid akin to those used to treat allergies and inflammation. Once in the bloodstream, cortisol prompts a multitude of changes. It prompts the liver to release glucose, a substance vital to rapid exercise, and acts to release fat, an excellent source of fuel for the body. It also acts inside the cell nucleus, instructing selected genes to increase or decrease their activity. The effect is typically an increase or decrease in the production of enzymes, which themselves regulate the rate at which various activities occur within a cell. So the impact of cortisol is quite wide-ranging, going to the core of cellular activity and the body's ability to marshal the energy it needs to respond to the perceived threat.

Both too much and too little cortisol in the blood can have adverse effects on health. Too little results in an inability to marshal energy in cases where a strong stress response is needed. Also, with a shortage of cortisol the body's immune system can become overactive, prospectively leading to allergies or other types of autoimmune disorder. Too much cortisol has the opposite effect, with the immune system becoming suppressed and the individual becoming more susceptible to disease.

Immune Suppression and Overactivity

Now the story becomes more compelling. Cortisol is one of a class of steroids known as glucocorticoids (hormones also released by the adrenal glands), which exercise a profound influence on the immune system. The immune system represents far more than the body's ability to ward off colds and infectious disease. In the words of behavioral biologist Paul Martin, it is ". . . a breathtakingly complex and subtle entity whose intricate workings are still far from being fully understood . . . one of the great wonders of nature, rivaled only by the brain in its intricacy and elegance of design. It is a multi-layered system of biological defenses . . . a highly complex and coordinated array of interrelated, interacting elements."

More than one researcher has compared the workings of the immune system to those of a nation, a society, or an economy. As with those entities, the immune system cannot be localized. Its components are located throughout the body: in the thymus (at the front base of the neck), the spleen (below and behind the stomach), the lymph nodes (clumps of tissue in the armpit, groin, neck, and elsewhere), the bone marrow, the tonsils, and especially the appendix. Immune cells -- white blood cells, or leucocytes -- are also found in the blood, where they travel anywhere they are needed, particularly to areas of injury or infection. The action of these cells produces the familiar inflammatory response as the blood supply is increased to the affected region and the blood vessels expand and surrounding tissues swell up.

Most important in the immune response is a type of white blood cell called a lymphocyte. These, in turn, are subdivided into B cells and T cells: the former produce tiny proteins known as antibodies that attack bacteria, viruses, and other foreign invaders in our bodies; the latter attack the foreign invaders without producing antibodies. There are several classes of T cells, too. Helper T cells stimulate the B cells to produce antibodies, suppressor T cells shut off the others when enough antibodies are around, and natural killer cells go right to work by attacking the invaders.

Seen in its entirety, the immune system serves as a virtual map of the body, including the brain. But it is something more. Like a nation or a society, the immune system possesses its own identity. It recognizes what is foreign almost instantaneously. In this respect, it is quite like the nervous system, which detects and responds to stimuli in the outside world and forms a lasting memory of those stimuli. In this way, the brain learns; so does our immune system, not in a cognitive sense but physiologically. It is effectively our body identity just as the nervous system (which includes the brain) can be said to represent our cognitive awareness. Together, they make up our self.

This biological reality of the self is further cemented by cumulative evidence of the extent to which the nervous system and the immune system communicate with one another. Their dialogue is constant. Forget the fairy-tale notion of the brain collecting data and barking orders. Sometimes it does that, but just as often it is on the receiving end of information and alerts. Of course, the communication is so rapid-fire as to render the issue of sender and receiver, for all intents and purposes, moot. The two systems, nervous and immune, speak the same language. The same two languages, actually. One is electrical, consisting of impulses conveyed across yards of nerve cell connections. The other is chemical, with scores of hormones, neuropeptides, and other messenger molecules.

These two languages are not spoken by accident. Consider that, in the first place, the nervous and immune systems are actually hardwired to each other. Nerve endings have been found in the tissues of the immune system: in the bone marrow and thymus gland, where immune cells are produced and developed, and in the spleen and lymph nodes, where those cells are stored. Next, consider that the vast array of chemical messenger molecules that were once thought to be restricted to the nervous system but are now known to be active within the immune system as well. Third, consider that changes in any part of the nervous system -- whether produced by a brain lesion, a head injury, or abuse of drugs like alcohol, cocaine, amphetamines, and nicotine -- can produce an increase or a decrease in immune function. Last, consider that changes in immune function are often accompanied by changes in nerve activity. An inoculation, for example, which purposely introduces foreign cells into the body in a bid to increase particular immune system activity, will produce changes in the electrical activity of neurons in the hypothalamus and other parts of the brain.

The study of these linkages is called psychoneuroimmunology. As we saw in the last chapter, this pioneering field is making an ever more compelling case for the biological unity of self. Yet its assertions are hardly new. The renowned neurophysiologist Sir Charles Sherrington declared over fifty years ago that "it is artificial to separate [the physical and the mental] . . . they both are of one integrated individual, [who] is psycho-physical throughout." Eastern religions and philosophy, of course, have a long tradition of emphasizing that essential unity.

Manifestations of Prenatal Stress after Birth

With all that as a backdrop, let us now return to the question of how factors that affect a pregnant mother can possibly determine her baby's lifetime capacity for handling stress and predispose that child to a range of challenging conditions. We've seen that the placenta intimately connects mother and child, preventing some harmful elements from passing through to the child but not denying them completely. In cases where the mother's adrenal glands are stimulated to produce copious amounts of the stress hormones noradrenaline, adrenaline, and -- especially -- cortisol (through activation of the sympathetic nervous system, the HPA system, or both), some of that cortisol will pass through to the fetus. In addition, the fetus itself is capable of secreting cortisol if it receives biochemical messages that all is not well. This constitutes its own stress response.

A stressed fetus is more apt to be born early because the adrenal glands also issue biochemical messages that signal the beginning of the birth process. In effect, these babies may be saying, "Let's get on with it; outside might be better for me than inside right now." Similarly, the adrenal activity of a mother who encounters a significantly stressful event or condition -- an upheaval in the family, for example, or loss of employment -- may lead to premature labor. Infants born prematurely, and whose nerve cell connections have not matured sufficiently, are prone to be more shy, anxious, and jumpier than average and to exhibit greater sensitivity to sound, touch, and other stimuli.

On the other hand, being born one or more weeks after one's due date may predispose an individual toward allergies. The fetus, in no hurry to be born, can be viewed as sending the message, "Everything's hunky-dory in here; no stress to speak of." This relatively stress-free state may prompt greater immune activity. Current evidence implicates a disparity in the balance between helper and suppressor T cells -- and the consequent number of circulating antibodies -- as the cause.

There is even evidence to suggest that schizophrenia is influenced by environmental programming. Because schizophrenia often runs in families, the standard inference is that its origins must be entirely inherited. The data, however, can be interpreted differently. In people with schizophrenia, brain size is about 2 percent less than normal, the hippocampus (a part of the brain associated with learning and memory) can be as much as 15 percent smaller, and the corpus callosum (the bundle of nerve fibers that connects the brain hemispheres) is thinner than it is in people who do not have schizophrenia. Alternately, epidemiological data imply that schizophrenia could result from wintertime viral infections, as more people born in late spring and early summer come to suffer from the disease. Their mothers would have been pregnant with them during the winter months, when the flu and other viral infections are common. The jury is still out on this association, however.

Still other evidence suggests that many people with schizophrenia suffered physiological complications at birth or in utero. One study, for example, indicates that mothers with an elevated blood lead level are twice as likely to bear children who, decades later, go on to develop schizophrenia. The suspicion is that exposure to lead destroys nerve cells in a fetus's growing brain.

The bottom line with schizophrenia, as with so many other conditions long thought to be exclusively genetic, is that while the disease undoubtedly has genetic roots, the sprouting of those roots depends on adverse environmental influences to which the developing baby's brain is exposed. This would explain why one identical twin may become schizophrenic yet the sibling does not.

Alcoholism and drug abuse also demonstrate the significant effect of programming on the developing child. Once again, the key is stress. It turns out that glucocorticoids, in addition to mobilizing the body's resources in the face of a threatening situation, stimulate the same reward pathway in the brain that is stimulated by drugs of abuse. The reward is release of the neurotransmitter dopamine, which usually occurs in response to pleasurable events. The effect has been demonstrated experimentally with rats (a species prone to considerable stress, almost all of it the result, seemingly, of encounters with human scientists). One study found that ". . . placing mother rats during their last week of pregnancy in narrow plastic cylinders three times a day caused their offspring to grow into adults that produced more [cortisol] during stress than rats that had not been prenatally stressed. The prenatally stressed rates were also regular drug fiends, sticking their nose through the cage hole to receive amphetamine infusions about two and-a-half times more than rats that had experienced a more relaxing time in the womb."

Human beings, most likely, react in the very same ways, and not just because of experiences in utero. In a study conducted by the Centers for Disease Control and Prevention and Kaiser Permanente, it was found that children who experienced child abuse -- an extreme form of stress -- have double the likelihood in adulthood of becoming addicted to nicotine or alcohol, and astonishingly enough, triple the likelihood of becoming addicted to harder drugs. Fortunately, not everyone programmed in such a way necessarily becomes an addict. The abiliy to control one's situation, or at least to cope with it, offers the prospect of minimizing the harmful effects of stress.

Infants and Touch

A mother or maternal caregiver can also counteract the effects of programming -- and, in any case, promote optimum development of her newborn. The avenue is "hands on" maternal affection. As articulated by Montagu, the benefits of such closeness are undeniable. Mammals' widespread licking of their young, for instance, is probably designed to keep the sustaining systems of the both the mother's and the child's body "adequately stimulated . . . through the activation of essential hormonal and other changes." Among domesticated or laboratory animals (e.g., sheep, monkeys, and the ubiquitous rat), numerous studies have confirmed that the "handling or gentling of [these] animals in their early days results in significantly greater increases in weight, more activity, less fearfulness, greater ability to withstand stress, and greater resistance to psychological damage." Young rats that are petted (or "gentled"), but in every other respect treated identically to unpetted rats, learn and grow faster and show greater liveliness, curiosity, and problem-solving ability. The evidence of enhanced brain development is clear, especially in the formation of the fatty sheaths that surround nerve fibers -- the glial cell conglomerations we mentioned earlier.

The most famous experiments in this regard are the ones conducted on monkeys by psychologist Harry Harlow. He noticed that laboratory-raised baby monkeys showed a strong attachment to the cloth pads that were used to cover their cages. Whenever these pads were removed for cleaning, the monkeys would try clinging to them and then engage in violent temper tantrums. Harlow got the idea to build a terrycloth surrogate mother, with a light bulb behind her that radiated heat. The result was a mother "soft [and] warm . . . with infinite patience, a mother available 24 hours a day. . . ." Harlow then installed a second surrogate mother built entirely of wire mesh, without the terrycloth "skin" and hence lacking in contact comfort. To complete the experimental set-up, some of the surrogate mothers were built to "lactate" (dispense milk) and others not. The lactating and nonlactating units were distributed equally among the terry - cloth and wire - mesh mothers.

The results were clear. The baby monkeys clung to the terrycloth mothers far more extensively than to the wire-mesh mothers, even when the wire-mesh mothers dispensed milk. Plainly, primate young overwhelmingly desire warm and nurturing physical contact.

Montagu writes that "the more we learn about the effects of cutaneous stimulation, the more pervasively significant for healthy development do we find it to be." "Cutaneous stimulation" is a catchall term for touch, licking, and gentling. A study of orphaned children bears out his statement. These particular children hailed from Eastern Europe; they had been raised in crowded orphanages with not much cuddling from adults, but were later adopted by foster parents in the United States. Despite their settling in with loving families, these children were found to have lower levels of certain hormones (vasopressin and oxytocin) that are associated with attachment and affection. The researchers concluded that children who have been deprived of gentle, caring touch from an early age may never surmount that deficit, as some of the key connections in the brain may remain substantially underdeveloped. Infants who are handled lovingly do not face this obstacle. They will also benefit, in the long run, through enhanced immune system functioning.

The consideration of immune functioning brings us back to the topic of stress. Montagu suggests that the relative immunity to the consequences of stress exhibited by gentled animals might be due to a less active HPA system, which, as we have seen, exerts long-term effects on an individual's health, either suppressing or revving up immunity depending on how much cortisol and other stress hormones -- especially CRH and ACTH -- are produced.

The experimental evidence with primates again supports this presumed mechanism. Charles Nemeroff, a psychiatry professor at Emory University and a leading voice on anxiety disorders, compared three groups of monkeys and their babies:

The young monkeys in the first group were reared in conditions in which there was plenty of good food available for their mothers. As a result, the mothers did not need to exert too much energy and mental effort in foraging. A second group of mothers had to work hard to find food. This high-foraging group was working at gathering food all the time. A third maternal group had a constantly changing availability of food, a very insecure situation that is difficult to adjust to. The infants of the mothers who had constantly to change their behavior were highly stressed. . . . [They] became pathologically shy when put in mixed social groups. Measurement of hormones in the [HPA] stress system showed that the levels were the same in the babies of the high- and low-foraging groups but were elevated in the variable foraging group.

Repeated findings from other such studies constitute, in the view of Nathanielsz, an overwhelming body of evidence that early life experiences -- especially maternal care -- can alter the set point of the HPA stress axis. In other words, the individual's inclination towards shyness, environmental sensitivity, jumpiness, and an exaggerated stress reaction will have been programmed for life.

Stress, Cortisol, and Depression

"We all know people," points out Nathanielsz, "who appear calm and collected under almost any circumstance. Stress certainly appears to be optional to them, or at least controllable to a level they can tolerate." On the other hand, we all "come across people who have a very short fuse and high anxiety levels." The latter appear to have extra-responsive HPA systems.

Excessive activation of both the HPA and sympathetic nervous systems is implicated in certain forms of clinical depression. People who are depressed tend to have higher levels of cortisol, adrenaline, and noradrenaline and, consequently, suppressed immune function. The interaction of depression and the immune system also manifests in other ways beyond the brain. Cytokines, which are proteins produced by immune cells that, in turn, cause inflammation, are notably higher in people experiencing distress, grief, and depression. Inflammation is linked to heart disease, so increased cytokine production may be a factor. By the same token, research has found that cytokine expression is reduced through laughter, that the arteries relax and blood flow is increased. The terms "light hearted" and "heavy hearted," it seems, may be reasonably good descriptors, not just of mood but also of heart function itself.

Still, depression is primarily thought of as a mental illness -- and the public associates a neurotransmitter, serotonin, with the condition first and foremost. Drugs such as Prozac, Zoloft, and Paxil raise serotonin levels by inhibiting the reuptake of serotonin that is released into neural synapses, thereby elevating the mood of people who are feeling down. (Interestingly, sunlight accomplishes the very same end.) And while neurotransmitters are typically associated with the brain, 95 percent of serotonin is actually found in the gut. So we see that "being down" is really a whole-body problem, not one confined to the head.

This is far from the complete picture because other elements of the immune system are more active in people with depression (making them more susceptible to allergies); this implies an undersecretion of stress hormones versus the higher levels we've noted of cortisol, adrenaline, and noradrenaline. "Unscrambling the precise mechanisms whereby depression acts on immune function is an immensely difficult problem," writes Martin.

Chronic Fatigue and Immune Function

The puzzle of immune function is thrown into particularly sharp relief in chronic fatigue syndrome (CFS). While the term "chronic fatigue syndrome" has come into use in recent decades, its cluster of symptoms (disabling tiredness, muscle pain, inability to concentrate, skin rash, vision problems, and sleep disorders) was first recorded in 2000 BC. Near the turn of the twentieth century, people with CFS-like symptoms were diagnosed as having "neurasthenia" or, just as frequently, hysteria. These conditions were said to be diseases of upper-middle-class women in much the same way that CFS was more recently derided as the "yuppie flu." That impression is only partially correct, however. While it is true that women are predominantly affected, some research has found the illness to be widespread among members of lower socioeconomic groups, with Latinos exhibiting higher rates than Caucasians. Likewise, though CFS is rarely thought of as affecting children, the results of at least one study done in the United Kingdom suggests that its incidence among kids might be underreported.

What is most striking is that the cause of CFS -- if there is a single cause -- has steadfastly refused to reveal itself. Lacking a genuine physical basis for the illness, many medical professionals (and others) have attributed CFS to psychological factors which, in their eyes, makes the condition suspect. The fact is that many CFS sufferers have symptoms that match the diagnostic criteria for psychiatric disorders and organic disease. Martin points out that the onset of CFS is often preceded by a viral infection; the condition is also associated with a persistent, low-level activation of the immune system. These facts give credence to the organic disease viewpoint. By the same token, many people with CFS exhibit signs of clinical depression, which sometimes seem to have preceded the onset. This buttresses the psychological viewpoint. The dichotomy only serves to affirm what disciplines such as psychoneuroimmunology and neurogastroenterology are pointing towards, namely, that mind and body are inextricably linked.

Some symptoms of CFS, incidentally, parallel those of another chronic condition known as fibromyalgia. In the former, severe fatigue is the major complaint; in the latter, intensive muscle pain takes precedence. As with CFS sufferers, people affected by fibromyalgia are not simply imagining their symptoms: research consistently finds that the spinal fluid of those with the condition is marked by high concentrations of a pain transmitting chemical called substance P and lower than normal levels of the pain-reducing agents serotonin and noradrenaline. Individuals affected by fibromyalgia also tend to be hypersensitive to touch.

Fearful Personalities

Pain, whether chronic or intermittent, intense or negligible, is the feeling in the human catalog of feelings that is most closely associated with touch. A feeling that requires expression (as I have defined it) is an emotion. I now submit that, among all the emotions, there is none as primal as fear: none so vivid, so unmistakable in the body, or in such dire need of reactive expression. Fear requires a closer inspection, through the lens of neurobiology. In the process, we're bound to learn much that is essential to an understanding of selfhood.

Fear is the focus of Ned Kalin, professor of psychiatry and psychology at the University of Wisconsin at Madison. He also directs that school's HealthEmotions Research Institute, one of the few organizations in the world dedicated to illuminating the complex relationships between emotion and health. Kalin emphasizes that "fearfulness is one of the most basic . . . responses we can have. It supersedes everything because of its survival value." But fear as the dominant aspect of someone's temperament -- habitual fear, malingering fear, excess fear -- is debilitating to a person and can ruin one's social relationships. Kalin and his colleagues, therefore, are probing the basis of what they term a "fearful disposition," one marked by inhibition, withdrawal, and other indicators of a high degree of stress. What they've found is elevated levels of the hormone CRH in the cerebral spinal fluid of monkeys who have fearful dispositions, as contrasted with monkeys who are characteristically less fearful. The pattern holds at the three junctures tested: at eight months, twelve months, and three years of age.

As we saw earlier, CRH is produced in the brain's hypothalamus early on in the HPA stress response. CRH signals the pituitary gland to secrete another hormone, ACTH, in turn signaling the adrenal glands to produce cortisol to mobilize the rest of the body. That is the short-term effect of CRH. The long-term effect may be to influence a brain structure called the locus coeruleus, a tiny spot at the base of the brain that appears to direct the individual's attention to environmental events by virtue of its being networked with virtually the entire brain. Experiments with monkeys (different monkeys from Kalin's) demonstrated that the locus coeruleus becomes most active when the animals are presented with new and unexpected stimuli. So, in tandem with the hypothalamus, this structure may be involved in setting the individual's set point for vigilance (i.e., what level of stimuli will inevitably trigger a stress reaction).

The evidence that CRH plays a major role in the HPA stress axis is compelling. First, when this hormone is injected into the brains of lab animals, their fear reaction lasts for hours (unlike reactions from other neurotransmitters). Second, CRH is less evident in the brains of rat pups whose mothers groomed and licked them than in rat pups whose mothers did not engage as much in this behavior. And monkeys who freeze in place when a person they don't know enters the lab have higher amounts of CRH as well as cortisol. This freeze response -- which is neither flight nor fight, but akin to both -- may evoke its own particular pattern in the bodymind. We'll explore this possibility later on.

Until now, we've been discussing brain structures located in what is known as the limbic system, a region that evolved much earlier in our history than the neocortex, which is the modern, "thinking" brain. The limbic area is the brain's emotional center, evaluating sensory information in primitive terms of friend or foe, threat or attraction, pain or pleasure. The neocortex, in contrast, is a much more recent addition, literally surrounding the emotional core. It is the part of the brain in which we engage in rational thought, mull over concepts, and make plans.

Kalin and his colleagues -- principally Richard Davidson, also of the HealthEmotions Research Institute -- have found that the right frontal part of the neocortex displays more electrical activity in monkeys that are characteristically fearful, whereas the left frontal portion is more active in monkeys that are less fearful. And it's not just evident in monkeys: the same pattern has been identified in young children. It is important to add, however, that not all children who are shy, hesitant, or fearful at an early age will necessarily remain that way. One study found that a majority of children who were timid at age two were no longer marked by timidity at age four. Another study found exactly the same vector between the ages of three and nine. So, in this case at least, biology is not destiny. By learning to be more extroverted, individuals will no longer display the right/left frontal asymmetry, nor have continuously elevated CRH and cortisol levels.

On the other hand, a person who does not grow out of early shyness may well retain these characteristics. Davidson has noted consistent differences among adults in the way their frontal cortex is activated during emotional states like anger or pleasure. Using advanced brain scan technology, he says, "We can see that some people will have more right-sided response to the emotion, some will have more left-sided response, and that both responses will remain relatively constant over time in those individuals." In addition, he finds that people with increased left-side activation generally report being happier than people with higher right-side activation.

This left-side/right-side distinction can be pictured via an analogy. Think of characteristic left-sided activity as a predisposition for approach, and a right-sided tendency as a predisposition for avoidance. The former conjures up descriptions such as openness, exploration, curiosity, boldness, enthusiasm, and resilience; the latter brings to mind associations with wariness, concern, anxiety, caution, negativity and, of course, shyness. Another way to sum up the differences is with the concepts extroversion and introversion.

Over the past three decades, Jerome Kagan, a psychology professor at Harvard University, has been studying introverted and extroverted children. He put forward the theory that arousal level (i.e., reactivity) is inherited, although learning can significantly modify its expression. One piece of evidence is that the anxiety levels in identical twins studied resembled each other far more than in fraternal twins. And a leading measure of arousal -- heart rate -- is distinctively higher in fetuses that grow up to be inhibited children than the heart rate of other fetuses. However, the evidence can just as easily be interpreted as supporting the view that environmental programming is at work. (It does not appear that Kagan and his associates probed for stressful influences on these children's mothers while pregnant.) One conclusion that can be unequivocally supported is that the characteristics of self begin to coalesce before birth.

Another observation made by Kagan is that the introverted children he studied were more prone to hay fever and eczema -- as were their relatives. As has already been suggested, there is reason to believe that allergies (which represent an overactive immune system) should correlate with lower-stress pregnancies, delayed births, and lower than normal levels of cortisol. The flip side is that higher stress during pregnancy, elevated cortisol levels, and exaggerated reactivity should all be associated with immune suppression, not allergies. The tendency toward some forms of allergy among shy children, therefore, is puzzling. Perhaps the changes associated with birth -- moving from a warm, nurturing environment into the bright, loud, cold environment of the hospital room -- in some way reprograms their HPA set point, and hence their immune predisposition. Or perhaps the mothers of some of these children encountered a physical complication at birth, with attendant stress and the same effect. Or, maybe these children's early nurturing was so full of loving physical contact that their immune disposition was, again, counteracted. Or possibly all of the above had some effect. The whole subject of immune function is terribly complex, as we saw with depression, and is just beginning to yield its secrets. In any case, Kagan's findings are consistent with those of a host of others, so an underlying mechanism needs to be found.

The Right Orbitofrontal Cortex

The portion of the brain that Kalin, Davidson, Kagan, and others have been focusing on -- the right frontal cortex -- is fascinating for yet another reason. On its underside is an area called the right orbitofrontal cortex. This critical region functions as a regulator of emotion, much as the hypothalamus serves to monitor and regulate basic needs such as food and sex. Neuroscientists -- particularly developmental neuroscientists -- are greatly interested in this region, since our development as rational, emotionally literate beings depends so much on the balance between our expressing feelings and exercising conscious control over them. As was noted previously, the orbitofrontal cortex is a major area of convergence in the brain, connected with the older, feeling structures as well as the newer, thinking areas.

Interestingly, no part of this region appears to be on-line at birth. This probably owes to the fact that the fetus, while clearly experiencing feelings, is not able to express them terribly well in the womb. There simply is not much room to do so. Upon birth and release into the wide world, the possibilities for emotional expression literally open up. The right orbitofrontal cortex then has something to do -- and what a job it is!

According to Allan Schore, a widely respected neuropsychiatrist at the University of California at Los Angeles, this part of the brain is not only central to our emotional life but, as a consequence, must figure prominently in any assessment of selfhood. The infant's interaction with caregivers essentially feeds the orbitofrontal cortex, especially during the first two years of life. Major disturbances over this period "can lead to very different psychosomatic . . . and personality problems." Child abuse or neglect would definitely qualify as one such disturbance. Another is accidents, particularly a head injury, since the orbitofrontal areas are susceptible to hematomas, contusions, and similar injuries. There is evidence that such damage may lead to a whole range of sensory distortions in later life, including visual and auditory apparitions and phantom smells and tastes. Another consequence may be a disturbance of the immune system, because allergies are said to emerge or to worsen among children and adults with orbitofrontal damage.This hearkens back to the question I raised above, namely why introverted children should exhibit allergies. Perhaps an overactive right orbitofrontal cortex is to blame.

Developmentally, the bottom line is that healthy activation of the entire right hemisphere depends on the relationship of the infant with his or her primary caregivers. Love and care bestowed on the child foster development of the brain's mechanisms for assessing, controlling, and expressing feelings. Not only that, but a growing body of evidence also shows that the right hemisphere is deeply connected with our ANS, which controls the short-term response to threat, and the HPA system, which keeps us "stressed" over a longer period of time. Our very sense of self evolves from the emotional bonds of childhood, as rooted in the interwoven dynamics of the bodymind. Based on a firm neurobiological foundation, we become secure, attached people capable of discerning legitimate threats to our well-being, reacting appropriately, and ready to reach out to others with care and concern.

Mirror Neurons and the Foundation of Empathy

Now seems an ideal time to move into the subject of empathy, a quality without which civilized society itself would not be possible. In the last few years, researchers have discovered what they believe is the wellspring of empathy in the developing child and, for that matter, in the adult. That source is mirror neurons, brain cells whose role it is to reflect others' actions -- reinforcing, in turn, the cues that underlie social behavior.

Mirror neurons were found, serendipitously, by a team of Italian researchers who were probing the brain of a macaque monkey. They noticed a group of cells that fired not only when the monkey performed an action but also when it saw the same action performed by someone else, hence the term "mirror neurons." These cells do more than reflect another's actions, however. Mirror neurons also fire when an individual sees someone else experiencing a distinct sensation or feeling, such as pain, embarrassment, fear, or elation. As such, the cells seem to be associated with -- some would say they underlie -- empathy. The association makes sense given that mirror neurons are much less active in children with autism and one of the red flags of autism is difficulty understanding the viewpoint or experience of another.

Increasingly, researchers suspect that impeded development of mirror neurons in early childhood is a factor in attachment difficulties as well as a range of personality characteristics and even personality types. The Type C person, for instance (about whom we shall learn more later), is diffident and prone to anxiety. The person prone to become immersed in a task or an imagining -- a trait known as absorption -- could likewise be shaped by insufficient growth of mirror cells. Alternately, a person who's insufficiently able to empathize and build mutually supportive relationships could become a loner or, just as easily, a domineering corporate CEO. In all these cases, mirror neurons whose growth was impeded could result in a mature personality that's less than ideal.

The function of mirror neurons, in combination with the individual's threshold for nervous system reactivity (what we've termed the HPA set point) probably explains how certain people are more apt to "catch" other people's moods or be overly affected by personalities or emotional attachments. (In coming chapters, we'll examine such people in detail, as an inquiry into their neurobiology can, in turn, offer penetrating insight into the human condition.)

Neurobiologist Vilayanur Ramachandran, of the University of California at San Diego, goes so far as to predict that mirror neurons will "do for neuroscience what DNA did for biology" in shedding light on empathy, imagination, and "a host of mental abilities that have remained mysterious." Because these cells effectively "put ourselves in the shoes of another," the argument goes, they must be at the basis of feeling itself. "We start to feel [other people's] actions and sensations in our own cortex," says another researcher.

This point of view, which I call the silver bullet theory of emotion, makes two mistakes. First, it implicitly accepts that feeling originates in the brain, ignoring the fact that what the cells are mirroring is not another brain but a bodily action -- a movement, vocalization, or gesture -- presumably indicative of what that the other person is experiencing. I say "presumably" because some people are quite adept at deceiving through their body language while others are ambivalent, camouflaging the truth from themselves as well as others. In any case, mirror neurons rely on physical cues, so it is debatable whether the empathy that is believed to result truly originates in the brain.

The second error the silver bullet theory embraces is that mirror neurons are somehow a phenomenon unto themselves -- that they are the key to understanding emotion. This devalues the limbic region, which is universally acknowledged as the brain's focal point of emotional processing. I suggest that mirror neurons are not the enablers of empathy but rather the conduit to a fundamentally more important region of the brain. It is worth considering that our stored memories of how people tend to look or act in a given situation are relayed to the mirror neurons, enabling them to recognize certain actions within a given emotional context. The mirror cells would then take in what others are exhibiting more than decide, on their own, what is being felt.

Interesting though they may be, mirror neurons are probably not the home of deep-seated feeling. Instead, I propose, they are a sort of focusing device -- binoculars, if you will -- that trains our attention on other people. They are part of a system of emotional processing that itself is key to who we are as individuals. We are more than the by-product of our neural activity. The further we look into development in utero and in early childhood, the more this should become clear.

The Teenage Years

Throughout this chapter, we've been concentrating on the earliest stages of the formation of the self, particularly the months spent in the womb, followed by birth, infancy, and young childhood. Medical science and psychology used to hold that, by age five or six, one's basic personality characteristics were set because growth, at least neurologically speaking, was substantially complete. That view turns out to be mistaken. The preteen and teenage years are a time of remarkable tumult in the human brain and the endocrine (hormone) system -- far more than was ever thought. The newest findings cast a different light on the emotional upheavals of puberty, showing adolescents to be "crazy by design." Barbara Strauch, medical science and health editor of The New York Times, describes it this way: "The teenage brain . . . is still very much a work in progress, a giant construction project. Millions of connections are being hooked up; millions more are swept away. Neurochemicals wash over [it]. . . . The teenage brain is in flux, maddening and muddled. And that's how it's supposed to be."

Many parents have observed that the period of adolescence rivals the "terrible twos" for sheer, excruciating change. "The tantrums, the slamming of doors, the fighting, the name-calling, the animalistic behavior" are all on display, as one parent expertly enumerated. Teenagers themselves admit that their moods are all over the map and sweep over them suddenly, unbidden. Experts had thought the answer was simple: hormones. It is manifestly true that hormones cause more general discombobulation during the teenage years than at any other time in human development. Production of the sex hormones, testosterone and estrogen, begins as early as age eight in girls and age ten in boys. Over the next few years, the levels rise steadily, culminating in the onset of menstruation in girls at the average age of thirteen and the production of sperm in boys at around fourteen. The impact of hormones is hardly limited to the bodily changes of puberty. In the brain, testosterone and estrogen (quantities of which are produced by both men and women, by the way) "can make brain cells and branches grow or disappear, make neurotransmitters excited or calm, and, working on the inside of the cell, turn genes in the nucleus on and off." It's no wonder that teenagers seem, at various and sundry times, to be out of control: estrogen levels during adolescence, for example, are believed to increase anywhere from 650 to nearly 5,000 percent.

Other hormones are at work, too. Dopamine, a dominant player in the brain's pleasure and reward pathway, is present at a fairly high level, inducing teenagers to engage in risk-taking, thrill-seeking behavior.The bottom line is not only that teenagers' feelings feel more intense, but that their world may actually seem a brighter, more vivid, more compelling place than at any other time in their lives.

Concurrent with this hormonal tide, the brain of every adolescent undergoes a massive remodeling, which affects everything from logic and language to impulses and intuition. Neurons bloom exuberantly, with their axons and dendrites -- their sending and receiving antennas -- reaching out to connect with other neurons. In particular, the frontal lobes, which are the font of our thinking, planning, and self-regulation, peak in volume at about age eleven in girls and twelve in boys. Then a curious thing happens. After increasing to far beyond adult levels, "the gray matter in the adolescent brain . . . does an about-face and starts a steep trek back down." At least 15 percent and in some regions more than 50 percent of the neuronal connections formed earlier are ultimately pruned. The result: a leaner, meaner thinking machine.

Aiding and abetting this process are the glial cells, which, as you'll recall, outnumber neurons by a factor of 9 to 1. They increase their production of a fatty material called myelin, which insulates the neuronal antennae. Myelin production, in fact, doubles during the teenage years. This results in improved communication between brain cells and a noticeable leap in cognition. As neuronal pruning occurs, those connections will become fewer but also faster and more efficient.

The significance of this shift cannot be overstated. The frontal lobes encompass the prefrontal cortex (the right side of which, as we have seen, is associated with introversion) as well as the orbitofrontal cortex (the right side of which has special prominence in the conscious control of emotional impulses). Thus, as teenagers' brain cells blossom and then are pared back, what is being fine-tuned more than anything else is the "inhibition machinery" -- teens' ability to say no, to decide not to act impulsively. Progress in this area is shown from experiments with young teenagers, whose amygdalas (which are central to the instinctual responses of fear and anger) show markedly greater activity than they will during later adolescence or adulthood. As connections to the right orbitofrontal cortex become more fully wired up, young people can tether their feelings and choose a more reasonable course of action. They no longer feel at the mercy of their impulses, inclined to lash out or act on a whim. They are more focused and emotionally better controlled.

It is relevant here to point out that poltergeist outbreaks have historically been associated with teenagers and even preteens. The word "poltergeist" means, in German, "noisy ghost," and a poltergeist's characteristic activities -- making a racket, throwing things -- do indeed seem juvenile. I will return to this subject later on but, for now, let us consider that less than optimum connections between the limbic region and the neocortex may be responsible. Remember, too, that the sex hormones marking puberty begin to be produced in girls around age eight and in boys about age ten. Less well-known sex hormones, called androgens, appear as early as age six or seven. (Androgens emanate not from the testes or ovaries, but from the adrenal glands.) If a hormonal imbalance is to blame for some poltergeist outbreaks, the age at which such effects might be seen would precede by several years the timeframe we customarily think of as adolescence.

Additionally, it may be significant that graphs of electrical activity outside the skulls of infants and children show spikes occurring roughly at ages four, eight, and eleven weeks; four, eight, and twelve months; and two, four, seven, eleven, fifteen, and nineteen years. Harvard University psychologist Kurt Fischer believes that these electrical patterns mirror leaps in cognitive development. It would be interesting to determine how poltergeist agents match, age-wise, against this gradient, especially since odd electrical activity (e.g., lights, radios, and TVs turning on and off at random) is said to be yet another trick in the poltergeist's bag.

Regardless of whether changes in the preteen and teenage brain can explain this particular anomaly, it is plain that selfhood is a major theme of adolescence -- not just metaphorically, but also biologically. The body and the brain are both busily engaged in "becoming what they will be." In this regard, it may be significant that two of the conditions we touched on earlier -- depression and schizophrenia -- often burst on the scene during adolescence. (Think Holden Caulfield here, the troubled protagonist of Catcher in the Rye.) Is some fluctuation in hormonal activity responsible for the sudden onset of depression in some pubescent children? Is a dysfunction in the brain's pruning process to blame for schizophrenia, leaving affected individuals with too many neural connections bringing in too much extraneous sensory information? Both mechanisms have been proposed. Regardless of what the correct answers turn out to be, adolescence is clearly a time when major changes are in gear. In every case, the development of an autonomous self will be brought to fruition.

Nature Works via Nurture

Our discussion of what exactly is happening with teenagers raises anew the fascinating question of how much selfhood is driven by nature and how much by nurture. Previously, I compared a human being's development in utero with blueprints for a house (i.e., one's genetic instructions). I noted that elements of the final construction may differ from what the plans specified based on any number of environmental factors, such as the construction materials used, variations decided on by the builder, and so forth.

Nowhere is this interplay more evident than in what is being learning about depression. It turns out that stressful life events are significantly more likely to trigger depression in people who have a genetic predisposition for it. In a study carried out by British researchers, more than eight hundred individuals were tracked over a five-year period as they lived through crises such as a death in the family, the loss of a job, or the breakup of a relationship. One-sixth of this group had a high-risk version of a particular gene, as evidenced by their being two-and-a-half times more likely to develop depression. The researchers concluded that nature works, in this case at least, via nurture. Stressful experiences, which happen to everyone, are like falling off a bicycle. It's the person's genes that determine whether he or she is wearing a helmet. As New York University psychologist Gary Marcus puts it, "A gene is really not a dictator, but an opportunity." Or, one might equally assert, a huge potential pitfall.

This type of approach, which emphasizes environmental factors at least as much as one's genetic blueprint, holds great promise for untangling the myriad factors that might explain why anomalies occur in a particular household or to a particular person. After all, the hormonal and neuronal tides of puberty affect every boy and girl, and yet it is just one out of millions who goes berserk and shoots classmates. Similarly, anomalous events such as poltergeist phenomena are extremely rare. By looking to the individual's neurobiology, as well as to the environmental factors that affect selfhood, we may be able to determine how and why such oddities occur.

The Self and the Other

In reviewing the course we have followed, this much should be plain: the roots of the self are planted well before birth, in sensation and in stress. Our nervous systems develop in response to sensory input, and our immune systems develop in response to perceived threat. To fully appreciate the picture, though, one further element must be understood. This element has been so basic to our discussion -- hovering quietly behind virtually everything that has been said -- that it may have gone unnoticed. But now it needs to be made unmistakable: having a self requires distinction, separation from another.

Are you familiar with the term "codependent"? It refers to two people who rely so much on each other, whose strengths and weaknesses counterbalance one another so completely, that their individual egos are, for all intents and purposes, intermingled. Saying that two people are codependent is not a compliment. The situation is not a healthy one for either party because they are too wrapped up in one another to grow sufficiently as individuals.

The early situation in the womb is something like that for mother and child. All of the neonate's needs are provided for and controlled by the mother. Existence is serene. If the situation were to continue indefinitely, the mother could be seen as little more than a host and the neonate as little more than a parasite. But the situation does change: the fetus grows. Through sensory input -- touch and smell at first -- it begins to distinguish what is "out there" from what is "in here." Its nervous system develops. Then, the inevitable variations in its mother's diet, sleep, sexual activity, health, and emotions -- all of which stem from simply being human and not necessarily from any major stress or traumatic occurrence -- begin to be noted. The fetus is better able to read and react to the chemical messages that are associated with the mother's varying states, whether minute to minute, hour to hour, or day by day. These variations are the earliest, and most beneficial, form of stress. Increasing, the fetus gains an appreciation of its surroundings and the fact that they are surroundings. And the feelings that it has are the precursor to emotions that can be expressed when the fetus finally leaves the womb and can kick, scream, coo, burble, smile, squeal, hug, and otherwise express itself. Thomas Verny, author of The Secret Life of the Unborn Child, puts it this way:

. . . the unborn's ego begins to function sometime in [the second trimester]. His nervous system is now capable of transmitting sensations to his higher brain centers. . . . Say, for instance, that a woman's particularly hectic day has tired her [and her] unborn child. That tiredness creates a primitive feeling -- discomfort -- which brings the unborn baby's nervous system into play; his attempt to make sense of that feeling involves his brain. After enough of these episodes, his perceptual centers become advanced enough to process more subtle and complex maternal messages. (Like the rest of us, the unborn gets better with practice.)

. . . Anxiety, within limits, is beneficial to the fetus. It disturbs his sense of oneness with his surroundings and makes him aware of his own separateness and distinctness. It also pushes him into action . . . he starts erecting a set of primitive defense mechanisms. In the process, his experience of anxiety and what to do about it slowly becomes more sophisticated. What began as a blunt, displeasing feeling . . . acquires a source (his mother), prompts his thoughts about that source's intentions toward him, forces him to conjure up ways of dealing with those intentions, and creates a string of memories that can be referred to later.

This brings us back to a touchstone of this book: the body. Individual self-awareness, what Freud called the ego, is the perception of the bodily self. Of course, this is what our immune system recognizes on an unconsciousness, physiological level. Moreover, whenever we feel or otherwise perceive something, we are simultaneously experiencing the division between self and other. In this respect, we are creating finer and finer distinctions in a process that began in utero, accelerated sharply at birth, and has been continuing ever since. Our lives -- and, inextricably, our appreciation of space and time, form and substance, and all our other sensory experiences and feelings -- are invariably lived in the body. If we are "in touch with" ourselves, we are "in touch with" reality, and vice versa. That means that we demonstrate and express our emotions.

The very word "emotion" (built around the word "motion") alludes to the self becoming, not merely being. Life is constantly in flux, and so long as we are alive, so are we. Looked at a slightly different way, each of us is far more an activity than a thing. Consider that things are static, inanimate, but people are dynamic, constantly acting or reacting. Furthermore, it can be argued that what individuals do -- what we are ultimately about -- is constructing meaning. "Experience is not what happens to you," remarked Aldous Huxley, "it's what you do with what happens to you." Each of us, naturally and fundamentally, seeks to understand what life is about, to construct meaning, and to make sense of it all. Feeling and its outward expression from the body (emotion) is central to that process. Neuroscientist Antonio Damasio's landmark book, The Feeling of What Happens, captures this process in its apt title. Our selves are bound up with our bodies, our felt perceptions, and our active efforts to elicit meaning from life.

As we move on to consider other aspects of reality -- consciousness, energy, and anomalies that appear to defy that reality -- an understanding of selfhood and its basis in sensation, stress, immunity, and feeling will prove useful to always have in mind.

*Reprinted (without footnotes!) by permission of the publisher, Park Street Press. Copyright 2009, All Rights Reserved.

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