A review of the nervous, immune, and endocrine systems may be useful for some readers. I will identify some of the main bodily structures and chemicals that are relevant to the interactions of emotion and health discussed in this chapter.

The Nervous System

The nervous system is the communication network within the body, receiving sensory input (both internal and external), integrating it, and responding to the stimuli. It consists of the central nervous system (the brain, spinal cord, and their surrounding membranes) and the peripheral nervous system (all the other nerves throughout the body), which both are structures of neurons.

The peripheral nervous system is subdivided into two categories: the sensory-somatic system (which coordinates the senses and the muscles that are under voluntary control) and the autonomic nervous system, which consists of sensory and motor neurons that run between the central nervous system and various internal organs, such as the heart, lungs, and glands, which are largely involuntary in their functioning.

The autonomic nervous system has two components, the sympathetic and the parasympathetic nervous systems, which work in antithetical ways. The former serves to prepare the body for emergencies ("flight or fight" reactions) by such means as stimulating the heartbeat, raising blood pressure, and shunting blood to the skeletal muscles, brain, and heart. The parasympathetic system, on the other hand, returns the body functions back to normal after they have responded to stimulation by the sympathetic system. The sympathetic and parasympathetic systems rely on different neurotransmitters. Jointly constituting the autonomic system, they are considered to function involuntarily, though for many years it has been scientifically established that some advanced Yoga and Zen meditators can control such autonomic processes as their heart rates or their consumption of oxygen.

As for the central nervous system, we consider primarily the brain, especially its three main regions: the forebrain, the midbrain, and the hind-brain. The forebrain, or cerebrum, with its two hemispheres (connected by the corpus callosum), covers the rest. The outer layers of the cerebrum are the cortex; its gray matter can be arbitrarily divided into six lobes -- frontal, parietal, temporal, occipital, central, and limbic. The cerebrum is the center of conscious functions -- memory, will, intelligence -- and it processes all the sensory data. The frontal lobe controls motor activity and speech, the parietal controls touch and sense of position; the temporal controls the reception of sound. The pre-frontal area is the entire non-motor region of the frontal lobe; it is involved in mental concentration and abstraction. In the days when pre-frontal lobotomy was used on psychiatric patients, the result was a kind of emotional neutrality in which the patient showed no joy, sadness, or affection.

The limbic lobe (right under the cortex) handles smell, taste, and emotional responses. The limbic system includes three evolutionarily old structures: the olfactory system, the amygdala, and the hippocampus. The hippocampus handles the filing of new information into the long-term memory system. (It is not involved with either short term memory such as dialing a phone number that you just looked up, or with procedural memory, such as knowing how to play the piano or ride a bike.) The amygdala, an almond-sized organ on each cerebral hemisphere, is responsible for recognizing dangerous situations and sending out an alarm, especially to the sympathetic nervous system, in the form of fear. A monkey without amygdalas will show no fear when it meets an aggressive monkey or when a snake approaches. If there is bilateral damage to her amygdala, a human being cannot recognize fear in human faces and may naively trust any suspicious-looking stranger who comes along.

Below the cerebral hemispheres are the thalamus and, at its base, the hypothalamus, which is connected to the pituitary gland. The hypothalamus regulates homeostasis (e.g. of thirst, hunger, body temperature) and links the nervous system to the endocrine system. It is believed to play a part in the overt expression of emotion.

The mid-brain is only a passage between the fore and the hind-brain, where we find the cerebellum, which is also divided into two hemispheres, and which manages the muscle movements. The medulla oblongata, where the brain and spinal cord connect, is the locus of the reflexes that control the heartbeat, breathing, sneezing, vomiting, and other involuntary functions. The brainstem is involved in emotional reactions; one of its structures, the reticular formation is an alerting instrument that basically tells the rest of the nervous system: "Pay attention! Something significant is going on." Another structure in the brainstem is the nucleus accumbens, which is capable of producing extreme pleasure, sometimes similar to an orgasm. It is the main reward pathway of the brain; it creates good feelings after certain biologically important behaviors are performed (e.g. quenching thirst or having sex) and thereby reinforces these behaviors. Other brainstem structures are responsible for the facial expressions showing anger, joy, tenderness, and sadness. The septum is located in front of the thalamus. It contains the centers of orgasm and other sexual feelings.

Although the brain's two hemispheres are connected by the corpus collosum, they are each capable of carrying out most functions independently. Occasionally a person's corpus collosum has been severed to control a severe case of epilepsy. Afterward, the patient may seem quite normal. However, close examination shows that there are some specializations between the hemispheres. The left hemisphere is more talented in linguistic matters, while the right side is more oriented toward visual-construction tasks. Most people are either right- or left-handed -- a manifestation of the dominance of one hemisphere.

The Immune System

The immune system, which is responsible for protecting the body by recognizing and destroying foreign invaders (antigens) before they can make the organism sick, was formerly presumed to be autonomous -- not controlled by the nervous system. The immune system consists largely of white blood cells floating around in the blood and lymph systems. Immune defenses must be able to distinguish between the body's own cells (by a distinctive marker on their surface) and foreign cells (antigens) which carry other markers. An antigen triggers an immune response. Sometimes a mistaken immune system reacts inappropriately, fighting against some of the body's own cells; this is the manifestation of an autoimmune disease.

All blood cells originate in the bone marrow -- including lymphocytes, the small white blood cells that become the main agents of the immune system. But lymphocytes mature in different organs, becoming different types of immune cells -- B cells (B for bone marrow); T cells (T for thymus), or NK (natural killer) cells. Besides the lymphocytes, the immune system also depends on phagocytes, or cell-devouring cells, and the whole system communicates among itself by means of cytokines.

The B cells secrete antibodies, which attach themselves to target cells to eliminate them. Each B cell makes a particular type of antibody. Antibodies are protein molecules known as immunoglobulins, which are of several specialized types -- IgA (or Immunoglobulin A), IgG, IgM, and IgE. The T cells are also specialized, with some of them attacking cells of the self that have been damaged or infected. T cells secrete the cytokines that serve as messengers within the immune system. NK cells and some T cells contain chemicals to be used to kill antigens.

Some B and T cells acquire a memory. Thus there are certain diseases that you may contract only once; you remain immune thereafter because the next time the same pathogen enters your body, a B or T cell will recognize it and be prepared to destroy it.

There are also other mechanisms by which the immune system, nervous system, and endocrine system (hormones) communicate. For one thing, there appear to be fibers from the autonomic nervous system that extend all the way to the immune organs, allowing the neurons to communicate directly with lymphocytes.[1]

The Endocrine System

The endocrine system influences the immune system largely by secreting such hormones as cortisol, mainly in situations of stress. Cortisol may decrease the lymphocytes' responsivity. Also, epinephrine and norepinephrine, androgens, estrogens, and progesterone hormones may either enhance or suppress the immune system under differing conditions. Prolactin and growth hormone may have some immuno-enhancing effects.

Emotions and Neuro-chemicals

As I report in this chapter, Candace Pert considers peptides to be "molecules of emotion." If she is correct, can we conclude from this that each emotion is a specific chemical? Not quite. For one thing, a given ligand may have different effects on the receptors of different organs throughout the body. For example, the neurotransmitter serotonin is generally recognized today as producing a serene sense of well-being. (Some have called it a "Zen drug" because it produces a happy contentment that is calmer than those produced by other drugs that benefit one's mood.) Some of the highly effective anti-depressive and anti-anxiety medications such as Prozac work by inhibiting the "re-uptake" of serotonin in the brain, thereby leaving a larger quantity of it around in the system to continue working. But serotonin has other functions too that are quite different from emotion management. For instance, about 95 percent of the body's serotonin is produced in the gut, where it serves to regulate peristalsis and other functions I shall leave unspecified here. [2]

Besides, researchers have difficulty exploring the human brain. Their main way of deciding which brain chemicals are present is by taking samples of blood or saliva, but there is a membrane around the brain -- the "blood brain barrier" -- that filters the blood as it enters, so it is not obvious that the same chemicals would be present in the brain as in a sample of blood drawn at the same time. A better way of observing the brain at work is by Positron Emission Tomography -- a "PET Scan" of the head. Depending on what the person is experiencing, different parts of the brain will "light up" and the resulting Xray film will show where there are receptors that are binding with particular ligands.

Serotonin is a neurotransmitter that calms moods. It does this by inhibiting certain other chemicals -- (catecholamines) -- which heighten one's excitement and maintain a kind of vigilant watch in case "fight or fight" becomes necessary. These are adrenaline, noradrenaline,[3] and dopamine. The first two of these substances are nearly the same; the more stress a person is under, the more of these chemicals will be produced, though they may also be found in some more enjoyable situations as well, including, for example, during sexual arousal or when one is excited at a football game. Noradrenaline can raise blood pressure, increase heart rate, metabolic rate, temperature. A person who suffers from chronic stress or anxiety will have persistently high levels of adrenaline and noradrenaline.[4]

Stress also stimulates a whole flood of other chemical messengers, of which an especially significant one is the steroid hormone cortisol. It helps convert the body's energy reserves into a quickly accessible form, and it can also be useful medically for suppressing inflammation and allergies, but it takes a grim toll on the immune system. When we need cortisol, we of course want it but in general we should hope that the need arises rarely and briefly,[5] for chronic stress is a serious health hazard.[6] In fact, its impact on the body is almost exactly opposite to that of laughter; when scientists showed volunteers a funny video and then measured their blood hormone levels, they found that cortisol and adrenaline levels had dropped.[7] (Here and elsewhere, we shall find that popular entertainment products may be more valuable for health-preserving mood management effects than for any other purpose.[8])

The aforementioned neurotransmitter serotonin tends to produce calm feelings, improve self esteem, relieve depression, and prevent depression and anxiety.[9] Endorphins are opioids that create a mood of euphoria and kill pain naturally. They become active during physical exercise, producing the so-called "runner's high," and especially during sex.[10]

Phenylethylmine (PEA) is a neurotransmitter that is produced, not only in the body, but can be consumed in chocolate.[11] It gives a feeling of great joy and has been identified as one of the chemicals stimulating the feeling of falling in love.

Dopamine is the neurotransmitter that is receiving the most attention among researchers today. It seems to be vital for successful psychological functioning in several different ways, especially by enhancing the person's goal-directed motivation. Richard Depue and Paul Collins have shown that the personality trait called extraversion is probably mostly a matter of having an abundance of dopamine. They claim that there are two characteristics that together constitute extraversion: (a) interpersonal engagement (enjoying and valuing close interpersonal bonds, and being warm and affectionate) and (b) agency (being socially dominant and assertive, and having a sense of potency in accomplishing goals). They call extraversion a matter of positive incentive motivation. [12]Focusing on a project in a single-minded way may increase one's level of dopamine. In general, however, psychologists believe that people are born with different temperaments, and these traits predispose them to be either highly motivated or less so.[13] Depue maintains that highly motivated persons tend to be happier than others. "We have strong evidence that feelings of elation [that occur] because you are moving toward achieving an important goal are biochemically based, though they can be modified by experience."[14] It has long been established that extraverts are usually healthier and longer-lived than introverts,[15] and the difference may well be attributable to their differing levels of dopamine.[16]

Dopamine is the chief neurotransmitter in the brain reward pathway, a region in the middle of the brain that extends to the nucleus accumbens, near the front of the brain. Dopamine's activation of the reward pathway is how the person experiences motivation; it generates the incentive to learn and repeat adaptive behaviors -- what psychologists call "reinforcement." There are emotions involved in the experience of motivation.

After dopamine has done its job -- facilitating the transmission of a charge across a synapse, it is ordinarily sucked up quickly in the "re-uptake" process.

Oxtyocin is known as the "cuddle hormone," or the "bonding neuropeptide," as befits its most conspicuous effects. It is released in men and women during orgasm; it aids in sperm transportation in males; it facilitates the birthing process and breast feeding; it supports the emotional bond between mother and child; and it is involved to a lesser degree in all kinds of warm human relationships where there are attachments. Oxytocin levels increase somewhat during massages, for example, or whenever one exchanges smiles or hugs with others -- or even with one's dog! It has pain-killing properties, plus mildly sedative and anti-stress effects, such as reducing elevated blood pressure and cortisol.[17] It can be produced in response to imagery, hypnosis, meditation, and when remembering previous loving relationships.[18]

Oxytocin usually is released in situations where a combination of other hormones are also present. For example, after birth it is activated along with another hormone, prolactin, to create the bonding between mother and child. During sex it combines with endorphins, dopamine, and sometimes other hormones to intensify the pleasure and emotional attachment between the couple. However, some hormones tend to counteract oxytocin. Thus the presence of stress hormones such as adrenaline temporarily blocks the release of oxytocin, possibly impeding the experience or the quality of coitus and the post-coital afterglow. Both dopamine and oxytocin are present during sex, but when dopamine spikes, oxytocin decreases, and vice versa.[19]

On the other hand, the oxytocin produced may be, as Aristotle might have put it, "the wrong hormone in the wrong degree at the wrong time." Psychologist Diane Witt, who is studying the hormone, believes that it may be involved in pathological conditions. Sometimes its absence leads bonding to break down, so that mothers may neglect their offspring. At other times, too much oxytocin produced in connection to the wrong person may lead to inappropriate pair bonding such as pedophilia.[20]

Prolactin is secreted in both sexes during and immediately following orgasm. Its function is thought to be to terminate sexual desire until later. Some men have significant amounts of prolactin in day-to-day life; their sex drives are more moderate than men with low levels of prolactin. In non-mammals, prolactin is found in significant amounts in both sexes, encouraging nurturing behavior in new fathers, for example. People with high levels of prolactin are agreeable and cooperative. They are not very interested in sex, or in fighting, except when necessary to protect their young.[21]

The sex hormones are of two main types: androgens and estrogens, which are most abundant in males and females respectively. The most important androgen is testosterone, the hormone that is responsible for many of the masculine physical traits, as well as for certain distinctive psychological tendencies of males (e.g. lower verbal ability than females and a tendency to persist at what they start and to work longer at a task without being distracted). In differing quantities, it is necessary for the enjoyment of sexual activity in both males and females.[22] High levels of testosterone do not bring prestige or success to males; too many of them are rambunctious and quit school early. Low-testosterone people tend to be friendlier, more intellectual, and more interested in the welfare of others. Their marriages are usually more successful than those of high-testosterone people.[23]

Finally, I should mention pheromones. Scientists have found certain fatty acids in human vaginal secretions that attract the opposite sex. Also, armpit sweat contains pheromones that stimulate the romantic fantasies of the opposite sex. No one has claimed that pheromones are essential to human well-being, but they are apparently significant in their social impact.[24]


[1]D.L. Felten, S. Y. Felton, D. L. Bellinger, S. L. Carlson, K. D. Ackerman, K.S. Madden, J. A. Olschowski, and S. Livnat, "Noradrenergic Sypathetic Neural Interactions with the Immune System: Structure and Function," Immunological Review 100 (1987), pp. 225-260.
[2] Michael Gershon, The Second Brain (New York: Harper, 1999). This book explains more than you would ever want to know about the enteric nervous system. Located in the gut, this nervous system contains more neurons than the spinal cord, to which it is barely connected by a few thousand expendable fibers that can be cut without harming its functioning. That is why Gershon calls it a "second brain." Whether or not one agrees to call it a brain, it clearly is a third nervous system, in addition to the central and peripheral nervous systems.
[3] Adrenaline is also called epinephrine; noradrenaline is also called norepinephrine.
[4] Paul Martin, The Healing Mind: The Vital Links Between Brain and Behavior, Immunity and Disease (New York: St. Martin's Griffin, 1997) p. 131.
[5]Post-Traumatic Stress Disorder may actually change the brain permanently. Those suffering from the condition have prolonged elevations of cortisol, noradrenaline, adrenaline, testosterone, and thyroxin. See P. Ver Ellen and D. P. van Kammen, "The Biological Findings in Post-Traumatic Stress Disorder: A Review." Journal of Applied Social Psychology 20 (1990), pp. 1789-1821; and J. W. Mason, T. R. Kosten, S. M. Southwick, and E. L. Giller, Jr. "The Use of Psychoendocrine Strategies in Post-Traumatic Stress Disorder," Journal of Applied Social Psychology 20 (1990), pp. 1822-1846.
[6] More than 20,000 studies have been pubished linking stress to disease. Clearly, chronic stress is especially injurious. See Alan Watkins, "Mind-Body Pathways," in his edited volume, Mind-Body Medicine: A Clinician's Guide to Psychoneuroimmunology (New York: Churchill Livingstone, 1997) p. 12.
[7] L. S. Berk et al "Neuroendocrine and Stress Hormone Changes During Laughter," American Journal of Medical Science, 298 (1989), p. 390. See also Martin, p. 131. On the other hand, there can also be a problem when levels of cortisol are too low. A study of young boys at the University of Chicago found that those with consistently low salivary levels were known to classmates for their extremely aggressive behavior. See University of Chicago Medical Center Report: <>.
[8]Dolf Zillmann, "Mood Management in the Context of Selective Exposure Theory," in M.E. Roloff, ed. Communication Yearbook 23, pp . 103-123.
[9]Serotonin is not the only chemical that inhibits excitement; enkephalins and GABA work along similar lines, effectively reducing pain, stress, and anxiety, and bestowing a calm sense of control and focus.
[10]On the other hand, we do not want to be too inhibited or calm, and fortunately the body produces other chemicals that elevate our emotions. Acetylcholine is a stimulant neurotransmitter derived from the female hormone estrogen. It may be involved in retrieving memories, and it supports alertness and sexual performance.
[11]Chocolate also is an anti-oxidant that has been credited with extending the life expectancy of males who eat it regularly.
[12]Richard A. Depue and Paul F. Collins, "Neurobiology of the Structure of Personality: Dopamine, Facilitation of Incentive Motivation, and Extraversion," Behavioral and Brain Sciences Vol. 22, No. 3, June 1999, pp. 491-517.
[13]Richard A. Depue, Monica Luciana, Paul Arbisi, Paul Collins, and Leon Arthur, "Dopamine and the Structure of Personality: Relation of Agonist-induced Dopamine Activity to Positive Emotionality," Journal of Personality and Social Psychology 67, No. 3 (1994), pp. 485 -95.
[14]Depue, as quoted by Deborah Blum, "Dopamine: The Plunge of Pleasure," Psychology Today Sept. 10. 1997, p. 46.
[15]Depue, personal communication; Deborah D. Danner, David A. Snowdon, and Wallace V. Friesen, "Positive Emotions in Early Life and Longevity: Findings from the Nun Study," Journal of Personality and Social Psychology Vol. 80, No. 5 (2001) pp. 804-813; C. Peterson, M. E. P. Seligman, and George E. Vaillant, "Pessimistic Explanatory Style is a Risk Factor for Physical Illness: A Thirty-Five year Longitudinal Study," Journal of Personality and Social Psychology 55 (1988) pp 23-27.
[16]Depue et al, European Journal of Personality Vol 9, (1994).
[17] It has been observed to reduce cortisol by 50 percent in animals. See C. Sue Carter, "Neuroendocrine Perspectives on Social Attachment and Love," Psychoneuroendocrinology, Vol. 21, No. 8, pp. 779-818, 1998.
[18]K. Uvnas-Moberg, "Oxytocin May Mediate the Benefits of Positive Social Internation and Emotions," Psychoneuroendocrinology , Nov. 1998, Vol. 23, No. 8, pp. 819-35; research by Rebecca Turner, psychiatry researcher at University of California, San Francisco: "Hormone Involved in Reproduction May Have Role in the Maintenance of Relationships." July 14, 1999. Also, George Bubenik, "Is Love a Kind of Addiction?" <>.
[19]Crenshaw, p. 135.
[20] Susan E. Barker, "`Cuddle Hormone`: Research Links Oxytocin and Socio-sexual Behaviors," Inside Binghamton University, Tuesday, April 11, 2000, p.1.
[21] James McBride Dabbs with Mary Godwin Dabbs, Heroes, Rogues, and Lovers: Testosterone and Behavior (New York: McGraw-Hill, 2000) p. 169.
[22]Dabbs, pp. 45-46.
[23]Dabbs, p. 156.
[24]Dabbs, pp. 46-47.