The Folly of Fools (20 page)

Within a species, the more time individuals can spend sleeping, the higher are their white blood cell counts for most cell types, while red blood cells, which originate from the same tissues but are not part of the immune system, are unaffected. This correlation applies to both REM sleep (with dreaming) and non-REM sleep. Perhaps the most striking fact about the hidden benefits of sleep comes from comparing different species of mammals. Individuals from species that spend more time asleep are less likely to be infected by parasites. Mammal species range from those that sleep as little as three hours a night to those that sleep more than twenty-one. Across this range, species with ten more hours of sleep per night have rates of parasitism twenty-four times lower. In short, for long-sleeping species, life may be dull, but it sure is healthy. It is worth noting, however, that sleep and dreaming play complementary roles in consolidating memories acquired during wakefulness. Both are required for initial memory storage and then several days later, spreading the memories to the neocortex—the more social part of the brain. So for all we know, small species of mammals (with long sleep) may have superb memories.

We should also note that deliberate sleep deprivation, as practiced in various penal colonies and torture centers around the world, is expected to increase parasite attack on the victims (on top of its other negative effects).

TRADE-OFFS WITH IMMUNITY

Trade-offs appear to explain major hormonal correlates of immune activity. For example, testosterone suppresses immune function in males. Since increases in testosterone are associated with both sexual opportunities and aggressive threats, the body faced with either one appears in effect to be saying, “I will deal with my tapeworm later; right now I’ll use some of those immune resources to defeat a rival male, or perhaps enjoy an extra copulation.” Consistent with this, among the lowest testosterone levels are those found in men living monogamously and with children; next higher, monogamously and without children; higher still, monogamously with outside sexual activity; and highest of all, no children, no partner, in full competition. In fact, some homosexual men show the highest levels of testosterone of any, perhaps for just this reason: no parental investment, minimal marital ties, maximum male-male competition.

Health maps inversely on testosterone. Marriage tends, for example, to increase life span in men. As expected, work on monkeys, apes, and humans shows that males with higher testosterone are more likely to become infected (with such diseases as malaria) and that disease itself lowers testosterone levels—in other words, the body lowers testosterone levels to shift investment to its immune system. There is nothing magic about testosterone. It is only a signal, not a source of potency. Some of the same correlations are found in insects, in which testosterone is not involved: males have a weaker immune system than females and suffer higher parasite loads and lower survival, just as in most mammals. This difference is probably general to most animals—certainly males typically suffer higher mortality. A testosterone-associated trait—degree of fat-free muscle mass—is associated with greater self-reported sexual activity in men and earlier age at first sexual experience. The trait is also associated with higher energy consumption and lower immune function.

Likewise, corticosteroids—produced in response to stress and associated with anxiety and fear—are immune suppressors. For example, subordinate monkeys who are harassed by dominants are often high in corticosteroids and low in immune function. The immune correlation suggests that the immune system is making resources available for dealing with whatever is causing the stress and, in any case, for maintenance in the face of anxiety and fear—even if doing so temporarily increases risk of disease. (Of course, the effects of prolonged stress are another matter.) In short, whether we are pumped up on testosterone or empowered by a corticosteroid such as cortisol, we sacrifice our long-term internal defenses for short-term gains. We shall soon see that this may be yet another cost of self-deception, hyping the aggressive or the threatened, with adverse immune consequences.

The brain is also a very costly organ. Although representing only 3 percent of total body weight, the brain consumes 20 percent of all resting metabolic energy. When a person is awake, this price seems to be invariant. In the 1950s, it was shown that doing arithmetic did not require additional mental energy, a finding that now seems quaint, given that the 20 percent energy cost is known to be constant whether you are happy, depressed, schizophrenic, or on an LSD trip. The cost is slightly diminished during nondreaming sleep but slightly elevated during dreaming. Thus throughout the full twenty-four-hour cycle, the brain’s resting energy cost remains virtually constant. In our species, 20 percent is the price of poker—the price to play life with a functioning brain. You must pay it or else. Indeed, not paying it for five minutes typically leads to death or, at the least, irreversible brain damage. This is just a fact of life—and an extraordinary one at that.

The invariant cost is important because one might easily imagine that different psychological functions have different energetic costs. Perhaps part of the benefit of depression is that the brain thereby saves energy. No—depression appears to have no effect on the 20 percent of energy the brain extracts. If depression lowers energy demands, it does so by lowering overall activity and metabolic rate. Likewise, if repression (suppression of truth from the conscious mind) lowers immune function, as it appears to, this is unlikely to mean that repression itself requires extra energy over and above normal function, the energy being supplied by the immune system. Instead, we must look for other changes associated with repression—which the immune system then pays for.

It has also been known for some time that the brain is the most genetically active tissue in the human body. In other words, a higher percentage of genes are active in the brain than in all other tissues, almost twice as high as in the liver and in muscle, the nearest competitors. A good one-third of all genes are so-called housekeeping genes, useful in running most kinds of cells, so they are widely shared, but the brain is unique both in the total number of genes expressed and in the number expressed there and nowhere else. By some estimates, more than half of all genes express themselves in the brain: that is, more than ten thousand genes. This means that genetic variation for mental and behavioral traits should be especially extensive and fine-grained in our species—contra decades of social science dogma. This includes, of course, such traits as degree of honesty and degree and structure of deceit and self-deception.

What we do not know is what the parallel facts are for our immune system. How much of our genes are also activated there? Are there important chemicals common to both the brain and immune system so that depletion in one system causes problems in the other? Certainly we would expect there to be, and if there are we would expect to see immune/psychological correlates we would not otherwise imagine. An analogy may help. Beginning in 1982, it was shown that female birds choose brightly colored males as a way of getting parasite-resistant genes for their offspring. This result has been documented many times since then—both that females like brightly colored males and that such males are relatively low in parasite number. It seems to be difficult to be brightly colored and sick at the same time, but why? Only in the 1990s was it shown that carotenoids—which give us orange, yellow, and red and which are not manufactured by any vertebrate but must come from their diet—play a vital role in immune function. This means that a more active immune system—for example, in response to infection—must draw carotenoids from surrounding tissues to help fight the invaders, as indeed it does. Those that are strong and healthy have color to spare, which they move to the body’s exterior as an advertisement.

Are there important brain function genes that also have immune correlates? A possible example was first described in a honeybee. When the bee is given a harmless antigen to which it mounts a response, the response interferes with associative learning but not with perception or discrimination. Since it is unlikely that any of these activities increases the brain’s energy budget, the explanation must lie elsewhere. In honeybees we know that associative learning depends on octopamine, a chemical that happens to be important in their immune system. In vertebrates we know that cytokines produced by the immune system can directly affect the hippocampus and reduce memory consolidation, but the functional meaning is obscure. We know that parasitic infection has a dramatic and negative effect on learning abilities. This effect must result because the activated immune system deprives the brain of other chemicals vital for learning—or has other effects, such as a decrease in sleep or dreaming, both known to be vital in consolidating learning in various species.

In birds there is clearly an intimate relationship between the immune system and the brain, one that appears to be heightened by the action of sexual selection. Two organs are intimately involved in immune function (mostly B cell production and storage)—the bursa of Fabricius of juvenile birds and the spleen of adults. The relative size of these two organs is positively associated with relative brain size across a range of species: the bigger the brain, the greater the investment in the immune system.

This may in part be due to big brains’being associated with long life span (which places a premium on parasite defense), but the correlation is especially strong when the sexes differ in brain size. That is, the bigger the relative size of the male’s brain compared to the female’s, the greater the relative size of the two key antiparasite organs in the species. The assumption is that males are especially likely to suffer from parasite load and its associated cognitive impairment (shown numerous times for birds), so that selection, especially in big-brained birds, will favor heavier investment in immune functions the better to protect against cognitive impairment. In this view, the two systems are complementary—the greater the investment in one (the immune system), the better the functioning of the other (the brain), presumably because the brain is especially vulnerable to parasite damage. For example, river otters that are parasitized by nematode worms show brain damage and reduction in brain size, but the effects are more prominent in males. In humans it has recently been shown that national averages in adult intellectual development are lower the greater the average parasite load.

WRITING ABOUT TRAUMA IMPROVES IMMUNE FUNCTION

In a series of important experiments from the 1980s to the 2000s, scientists showed that writing about trauma produced clear immune benefits. Although most of this writing was done in English, the same effect holds for Spanish, Italian, Dutch, and Japanese, that is, broadly. In one set of experiments, people were asked to imagine the most traumatic event in their lives. They were then split into two groups—those who spent twenty minutes each day for four consecutive days writing in a private diary about their trauma and those who wrote for twenty minutes each day on superficial topics (for example, what they had done that day). Blood was drawn before the experiment began, after the last day of writing, and six weeks later. Although those writing on their trauma said they felt worse at the end of the writing than those who wrote on innocuous topics, their immune system already showed improvement, which was still detectable six weeks later, at which time they also reported feeling better (than those who had not written about their traumas). In summary, the immediate feeling of confronting trauma is negative but the immune effects tend to be positive, and the longer-term effects on mood and immune system are both positive.

Note that the positive immune effect
precedes
the positive effect on mood, and how little writing is necessary to beget a measurable immune effect some weeks later. A recent review of about 150 studies confirms that there is a general pattern in which emotional disclosure, even in the form of occasional autobiographical writings, is often associated with consistent immune benefits.

Writing about trauma in a private journal in a lab is obviously an evolutionarily recent event, but it probably acts as a substitute for sharing this information with others. Certainly rituals of confession are common in most religions, whether public, as in many New World Amerindian religions, or private, as in the Catholic confessional. Indeed, the injunction to confess one’s sins to God herself in prayer may serve a similar disclosure function. The benefits of the “talking cure,” psychotherapy, may also arise in part from disclosing traumatic or shameful information that one is, in fact, hiding from others. When traveling, we will often tell secrets to complete strangers, people we have never met before and, crucially, do not expect to see again. The more that people talk in small groups, the more they claim to have learned from the group. As one psychologist drily notes, sharing our thoughts is apparently “a supremely enjoyable learning experience.” For this reason, particular theories of human development—say, Freud’s psychosexual stages—may be as valid as astrology, yet talking to one’s analyst may provide benefits for the same reason that writing in a journal does.

One important possibility is that some of these positive correlations may in fact be caused by effects on sleep. If disclosing trauma to others results in fifteen more minutes of sleep, or at least less fitful sleep, this alone could induce the known immune benefits. A striking effect of disclosure is how quickly the benefit kicks in, as would happen if it immediately led to less troubled sleep. One final feature of the work on expressive writing is worth emphasizing. Computer-based analysis has isolated three aspects of the writing that produce beneficial effects: emotion words, cognitive words, and pronouns. The more people use positive emotion words, the more their health improves. Even writing “not happy” is better than writing “sad,” perhaps because the focus in the first remains on the positive emotion. Using lots of negative emotion words and none at all are both associated with no benefit, while a moderate number is. Perhaps one is overwhelmed in the first case and in complete denial in the second. The value in taking alternative perspectives on a problem is suggested by the fact that changing back and forth from the first person (“I,” “me,” “my”) to all other pronouns (“they,”“she,”“we”) is associated with improvement, while remaining in one or the other perspective is not.