The Pleasure Instinct Part 7

Although the modern hedonic theory of addiction has addressed some limitations of the earlier hedonic model, there are still many open questions about how addiction occurs and what can be done therapeutically to intervene early. The perspective advanced here does shed some light on several issues. First, it provides a biologically based mechanism, consistent with evolutionary theory, for understanding why we are all susceptible to drug and alcohol abuse. The same neural mechanisms that promote normal brain development through birth and well into the adolescent years drive us toward certain stimuli that signal high fitness value.This biological imperative translated into improved odds for surviving to reproductive age in ancestral environments. Clearly, however, this process can lead us toward some stimuli and experiences that may have adverse consequences in our modern environment.

The theory suggests, then, that each of us-not just the few with an unlucky genetic disposition-is susceptible to addiction. From this perspective, it is not so surprising that many people become addicted to these substances. Indeed, it is perhaps most surprising that only a relatively small percentage of people who experience drugs actually become addicted. Of course, a great deal of variation exists from individual to individual in how these neural systems communicate with one another, and some of this is undoubtedly modulated by genetic influences. Much of the evidence discussed above indicates that these systems are also readily modulated by environmental experiences, including drug use, stress, and a host of other life circ.u.mstances.

Even a casual observer would note the persistent relations.h.i.+p between chronic stress and drug use. Chronic stress and the a.s.sociated activation of the body's response (for example, increased cortisol, adrenocorticotropin hormone, and corticotropin-releasing factor) have severe and deleterious effects on the neural systems that regulate emotions, including the pleasure instinct. Often these neural changes acc.u.mulate slowly, but they can last long after the stress has been reduced or even eliminated. For instance, in a landmark study, ethologist Dee Higley and colleagues showed that adult rhesus monkeys that were stressed for six months immediately after birth by being removed from their mothers exhibited increased stress responses (measured both physiologically and behaviorally) when compared to littermates who were allowed parental attachment during this critical period. Interestingly, the adult monkeys who were stressed at birth exhibited increased ethanol consumption under free-range conditions when compared to normally reared littermates. Monkeys that were not permitted to form a social attachment with their mothers during this critical developmental period grew up to be adults that exhibited greater fear and startle responses and increased physiological markers of stress (for example, cortisol production), and were more likely to consume a mind-altering substance than those that were able to establish a maternal bond during this period.

This is consistent with my experiences at the residential treatment house. Perhaps the most intriguing part of working at this facility was that the kids seemed to use drugs that elicited specific portions of the pleasure circuitry that compensated for the type of stress they were experiencing. Alberto, like many gang members, used methamphetamines to activate his mesolimbic and a.s.sociated neural systems, giving him a sense of high energy, confidence, and strength, all requirements to combat the stress that accompanied gang life. Christine, on the other hand, gravitated toward increased s.e.x and heroin use, which strongly activated her opioid system, eliciting a sense of calm and serenity-feelings that compensated for the abrupt loss of social attachment to her parents and grandparents. When adequate social bonds failed to develop (signaling a fitness decrement), Christine showed a tendency to engage the neural systems that promote feelings of attachment and calm through natural (via increased s.e.x) and pharmacological means.

Understanding how the pleasure instinct may contribute to drug-seeking, drug use, and addiction is important, since the theory has implications for treatment. For instance, much of the literature examining the biology of addiction has concentrated on the mesolimbic dopamine system. Drug use can alter this system in a number of ways, including (1) decreases in dopamine-containing cell size in the basal forebrain; (2) enduring increases in postsynaptic dopamine receptor sensitivity; (3) alterations in the release of dopamine from presynaptic sites; and (4) a cascade of intracellular changes that occur, which ultimately impact dopamine transmission. Each of these presents a possible therapeutic target for combating drug-seeking and addiction on the "wanting" side. However, our theory predicts that agents that downregulate dopamine transmission may also have anti-hedonic effects, perhaps making them less tolerable to patients.

When we consider experiences like those of Alberto and Christine, and add what is now understood about the different neural systems involved in the pleasure instinct, it is probably safe to conclude that not all drugs induce the same hedonic experience. Another potential therapeutic target might be the opioid system, using compounds such as oxytocin agonists and prolactin agonists, which have been shown to reduce separation distress in animal models. Clonidine, an alpha-1 noradrenergic agonist, has been shown to reduce separation distress in rats and is already being used effectively in clinical practice to amerliorate opioid withdrawal.

Clearly, far better than treating an addiction already in progress is to implement ways to limit the likelihood of people feeling disenfranchised from family and society in the first place. There is acc.u.mulating data showing strong relations.h.i.+ps among disruptions in normal social dynamics, drug use, and abuse.There is also a growing scientific literature demonstrating that both drug use and social bonding engage common pleasure circuitry. Providing additional social support structures, particularly for adolescents, might help reduce the likelihood of engaging these circuits through drugs and alcohol if they are experiencing social problems.

Finally, it should be said that the pleasure instinct offers but a single perspective on addiction. Certainly, no one theory explains all of addiction. Given what we now know about the disparate brain systems that different drugs engage, it is highly unlikely that there will ever be a single cure that fits all. However, as basic biological research continues to unveil the mysteries of how emotions are modulated by brain circuits, each new discovery presents a potentially novel therapeutic target. Understanding the environmental and experiential factors that also engage these circuits might offer therapeutic avenues that are just as appealing (or perhaps even more so) as those dreamed up by pharmaceutical companies. As we will see in the remaining chapter, modern life offers us a plethora of nonpharmaceutical ways to engage the neural circuits controlling the pleasure instinct.

Chapter 12.

Parsing Pleasure Though sages may pour out their wisdom's treasure, there is no sterner moralist than Pleasure.

-Lord Byron, Don Juan

All the labor of man is for his mouth, and yet the appet.i.te is not filled.

-Ecclesiastes

This book began with a single question: why does pleasure exist? A pa.s.sionate debate, framed on one side by hedonists and on the other by stoics, has raged since antiquity about the nature and utility of pleasure, and has influenced virtually all facets of social life in the Western world.Throughout the course of history popular opinion on the matter of pleasure-intermixed with its many political, legal, religious, and moral implications-has never found a stable resting point. Instead, it has swung back and forth like a pendulum. Conservative eras in which the pursuit of pleasure was, at least publicly, tempered have often been followed by more permissive periods, and vice versa.

Epicureans are usually thought of as representing an extreme position in this debate, one that advocates unchecked pleasure-seeking to the abandonment of all social responsibilities. Yet this is a modern distortion of Epicureanism, which originally held that happiness is attainable only if one distinguishes between pleasures that are natural and necessary, such as eating and drinking, from those that are simply desired. Ancient Epicureans followed a rather austere lifestyle, sacrificing some pleasures to avoid greater displeasures.

This philosophy laid the groundwork for the emergence of the sensualist ethics movement of the seventeenth and eighteenth centuries, a view that prevailed in the writings of thinkers such as John Locke and David Hume in England, and Francois Diderot in France. The central idea of this movement is that our senses are the final judge of what is positive or negative. Experiences that bring pleasure to the senses are deemed good, while those that displease are judged as bad. In this context the foundation for morality resides with the individual and is relativistic, a viewpoint that ultimately gave rise to utilitarianism in the nineteenth century.

This book entertains a third point of view that is distinctly different from those of the hedonists, who equate pleasure with happiness, and the modern-day stoics, who are guided by varying belief systems, yet at their core share an uneasy truce with pleasure. All of our emotions, including the experience of pleasure, have been shaped by natural selection to cope with challenges and opportunities that have recurred over the course of hominid evolution. In this context, pleasure may point us down a particular path, but it is not the final destination.

From a strict evolutionary perspective, the story of pleasure is often summed up in a few pages as one dealing almost exclusively with s.e.xual behavior and reproduction. s.e.x has been linked to pleasure through natural selection to maximize genetic propagation-end of discussion. As we've seen, however, the role of pleasure in human evolution and development is far more complicated and interesting.

The modern hedonic palate is amazingly diverse and shaped by a host of personality and cultural factors. The feeling of pleasure can be elicited by a wide range of experiences, each involving disparate sensory systems. Likewise, the expression of pleasure in terms of overt behaviors or verbal descriptions varies considerably within different contexts and cultural norms. Although each of us has unique likes and dislikes, there is a common core of sensations that the vast majority of humans label as pleasurable. Our preference for these core sensations arose though natural selection to ensure that we experience key sensory events during our early years that are required required for normal brain development. This does not mean that we are all destined to be attracted to exactly the same phenomena, but rather to the same general cla.s.ses of stimulus features. To really understand the choices we make in contemporary life, it is critically important to consider the modern problem of how cultural influences interplay with nature's program of sensory and behavioral preferences. for normal brain development. This does not mean that we are all destined to be attracted to exactly the same phenomena, but rather to the same general cla.s.ses of stimulus features. To really understand the choices we make in contemporary life, it is critically important to consider the modern problem of how cultural influences interplay with nature's program of sensory and behavioral preferences.

Addiction, for example, is certainly not a modern problem.There are historical accounts of addiction to everything from chocolate to s.e.x to war. As we have seen, at its root addiction is a biological phenomenon regulated by the brain circuitry that is involved in reward and motivated behaviors (see chapter 11). Clearly, however, cultural norms have a way of insinuating themselves into the biological mechanisms that control these behaviors.

Modern addiction-whether we are talking about heroin, alcohol, nicotine, over-the-counter drugs, gambling, or your favorite soap opera-is often said to be facilitated by two key elements: the ease with which a drug or experience is acquired, and the rate at which it activates the central nervous system. Smoking, for instance, is highly addictive because tobacco products are readily available, and nicotine rapidly activates the dopaminergic brain systems we discussed in chapter 11. A third element that should be considered is whether the focus of an addiction involves more than one hedonic preference. Many addictions involve compounded stimuli. One can think of these as complex experiences that are comprised of two or more fundamental hedonic preferences. Smoking and alcohol are both addictive in themselves, but are far more addictive when combined together. Indeed, becoming addicted to either smoking or drinking alcohol markedly increases the odds of becoming addicted to the other. This makes intuitive sense, since both forms of stimulation are activating the same brain reward mechanisms.

As we have seen, nature's list of hedonic preferences is long and taps into every sensory domain. This provides an enormous palate of sensory experiences that can be combined in culturally acceptable ways to form compounded stimuli. Toddlers are not terribly burdened by cultural norms, so the impact of compounded stimuli is most apparent in the things that grab their attention. The appeal of shows such as Barney and Friends Barney and Friends and and The Teletubbies The Teletubbies is easily understood when considered from this perspective. Both shows deliver daily doses of compounded stimuli that are sharply tuned to match several of the hedonic preferences we have been discussing. Included among these are stimuli formed by sharp contrasts, bright primary colors, p.r.o.nounced lateral symmetry, repet.i.tive sounds and movements, and exaggerated intonation and facial images. is easily understood when considered from this perspective. Both shows deliver daily doses of compounded stimuli that are sharply tuned to match several of the hedonic preferences we have been discussing. Included among these are stimuli formed by sharp contrasts, bright primary colors, p.r.o.nounced lateral symmetry, repet.i.tive sounds and movements, and exaggerated intonation and facial images.

Adults are not exempt from the lure of compounded stimuli, but their attraction to these experiences is shaped significantly by cultural expectations and previous life events. Memory and a.s.sociative learning link everyday stimuli to primary reinforcers, and this process plays a large role in determining what an individual finds pleasurable.

In the past three chapters we saw how the pleasure instinct crafts time-sensitive developmental preferences for certain types of stimuli that, in turn, can emerge as receiver biases in adults. There is probably no better place to look for examples of this process than the modern consumer world. In 1957, Vance Packard published his cla.s.sic book The Hidden Persuaders The Hidden Persuaders. This was the first broadly read account of how the advertising community was taking advantage of discoveries in a number of scientific disciplines to tap into subconscious processes for the benefit of product positioning.

Packard's book focused on psychological processes that might be important for making a product appear more desirable to a targeted consumer. Receiver biases may also make certain products seem more appealing; however, the mechanism can be clearly linked to developmental preferences forged by natural selection and, in some cases, magnified by s.e.xual selection.

Symmetry, proportion, and rhythm are particularly good examples of receiver biases that clearly have a home in the advertiser's toolbox. Our innate preference for these features has been studied by marketing scientists for decades and applied to everyday commercials. For instance, symmetry is a particularly ubiquitous feature of design logos for consumer products ranging from automobiles to home electronics, where the implicit message is one of-you guessed it-fitness. Indeed, virtually every major manufacturer of consumer goods today employs or consults sensory scientists to optimally align the aesthetic features of a product with Gestalt forms that are innately pleasing. These scientists spend a great deal of time getting customer feedback on potential product design, packaging materials, promotional displays, advertising placement, and so forth. These days I can no longer go into a department store and simply shop. Instead, I find myself counting the many ways I am subtly manipulated by the growing armamentarium of advertising/marketing devices supplied by modern sensory science, evolutionary biology, and neuroscience.

In chapter 3 we discussed the pioneering work of psychologists James Olds and Peter Milner, who in 1954 were the first to discover the so-called pleasure centers of the brain. Although modern brain theorists are still grappling with what is actually experienced when these sites are stimulated, an important finding is that a fairly restricted and well-defined set of circuits has been implicated again and again in literally thousands of studies. There are many ways to promote activation of these circuits via different sensory domains and experiences. Similarly, once these circuits have been activated, they may signal a diverse number of other brain regions that are responsible for the appropriate behavioral response.

Today it is unclear whether we should call the limbic circuitry involved in reward and motivation "pleasure centers." Olds and Milner stayed away from this terminology initially, but early theorists simply could not resist. Normal functioning of this limbic circuitry is implicated in several processes that seem to be related to pleasure. These include reinforcement learning through reward, consummatory behaviors such as eating food and mating, and appet.i.tive or motivated behaviors such as those leading up to the point of actually receiving the reward.

The portions of the brain where this circuitry resides are subcortical structures that have existed at least as long as the birth of mammals. The evolution of primates is a story that in many ways began with the limbic system and the behaviors/functions it supports. Nature rarely reinvents itself. The general pattern of brain circuitry one sees in limbic structures such as the hippocampus (for example, recurrent excitatory synapses modulated by feed-forward inhibition) forms the basis for much of what is seen in neocortical structures. The gradual emergence of the primate line was accompanied by neocortical development that was based on mammalian limbic circuitry.

This evolutionary sequence is echoed in the embryonic growth of humans. Each milestone of brain development that is traversed by the growing child is a reprise of our evolutionary past. Limbic structures give rise to neocortical structures, and, most importantly, limbic functions give rise to neocortical functions limbic functions give rise to neocortical functions. The basic emotions, including pleasure, laid the foundation for the gradual emergence of higher cognitive processes unique to human primates (for example, language and musicality). Parents see this process unfold daily as limbic functions such as finding pleasure in primary colors, faces, symmetry, repet.i.tive movements, and certain sounds direct babies and toddlers toward the necessary experiences that will guide the continual development of more complex functions that require a healthy neocortex.

With only twenty-five thousand or so genes const.i.tuting the entire human genome, nature is forced to conserve at every step. Developmental bootstrapping is an elegant compromise that engenders the individual with a rapidly growing brain and a built-in desire to seek experiences that will fine-tune this circuitry. This process has quite a bit of freedom and flexibility. It's somewhat akin to a robotics engineer getting the basic wiring and simple functioning working and then letting the machine do the rest of the programming based on a few simple rules. The first rule is that certain cla.s.ses of stimuli must be experienced during development to ensure that the programming is continued. The second rule is that the particular stimuli the robot encounters in these general cla.s.ses will fine-tune the machine to life in a specific environment.

Machines are generally not designed this way, of course, but biological organisms possess a delicate balance of preprogrammed growth that depends on experiential refinement. This freedom and flexibility has its costs. Addiction is the most obvious example of how bootstrapping as a general developmental process can lead to potential problems. Compounded stimuli are not just found in modern environments, but the ease with which so many different hedonic preferences can be satisfied at a moment's notice is clearly an oddity of contemporary life. In the twenty-first century we have extraordinary technological means to quench our thirst for pleasure, and the potency of addiction will increase when our drug of choice is mixed with other hedonic preferences.

These ideas and findings suggest a novel treatment strategy for dealing with addiction in the broadest sense. Focusing solely on the primary point of addiction (for example, smoking or consuming alcohol) will generally be less effective than identifying all of the hedonic preferences a.s.sociated with the behavior and treating the compounded stimuli as a whole. This perspective suggests, for example, that treatment for alcohol addiction should also include a therapeutic means to reduce smoking (if applicable) and curtail any increases in sugar consumption. Such a scenario is typically not part of alcohol treatment programs, many of which allow (or even encourage) subst.i.tuting one addictive substance for another-sweets in place of nicotine, caffeine in place of tobacco, and so forth. People often find it easier to treat addiction through subst.i.tution.You probably know at least one person who quit smoking or drinking alcohol, only to increase another behavior that is equally addictive.This happens with great frequency, since all hedonic preferences-regardless of the sensory domain (for example, taste, touch, vision, etc.)-stimulate the same brain circuitry involved in reward and motivation. Activity in this circuitry is regulated by a number of additional systems, with the aim of keeping it within a range of acceptable levels (allostasis).

Addiction is really just the tip of the iceberg. Understanding the role of pleasure in the modern context requires stretching back in historical time and considering its function in the evolution of our species. It also requires thinking about the role of pleasure in human brain development-from embryo through the toddler stages, into adolescence, and then adulthood. Understanding how pleasure influences our behavior is critical for parents who want to make intelligent choices about the growth environments they provide for their children. Yes, it is obvious that children need stimulation to develop along a normal trajectory, but not all stimuli are created equal. There are clearly optimal forms of stimulation that parents should bring into their children's world. The pleasure instinct will do the rest by causing the child to repeatedly engage in play with objects that have these features.

There is, of course, a tremendous benefit for adults as well. Pleasure has varied roles in our modern lives, many of which are influenced by its original developmental purpose. Understanding the original role of pleasure helps to frame the modern experience by revealing key features of our lives that it impacts, ranging from addiction to the influence of advertising on consumerism. Hedonic preferences do not simply go away as we grow older. While it is true that they become increasingly shaped by our experiences and cultural norms with age, they are still with us, anch.o.r.ed beneath all the top layers. There is no doubt that brain development hits its zenith in our early years, but it is a continual process throughout the entire life span. Old neurons die, new neurons are born. Since brain development slows significantly after adolescence, the role of pleasure in guiding this growth becomes less central. Nevertheless, the pleasure derived from experiencing the many forms of developmentally important sensations persists-a common gift shared by us all, yet flavored by our unique life events and conditions.

Notes.

1 Foibles and Follies 6 Until recently, scientists have Until recently, scientists have For an excellent review, see chapters in Ekman, P, Davidson, RJ (1997) For an excellent review, see chapters in Ekman, P, Davidson, RJ (1997) The Nature of Emotion: Fundamental Questions The Nature of Emotion: Fundamental Questions. Oxford University Press, Oxford, England.

6 Academics have typically s.h.i.+ed Academics have typically s.h.i.+ed But see Johnston,VS (1999) But see Johnston,VS (1999) Why We Feel:The Science of Human Emotions Why We Feel:The Science of Human Emotions. Perseus Publis.h.i.+ng, New York, NY.

7 Sociobiology and its heir apparent Sociobiology and its heir apparent Excellent introductions to evolutionary psychology include Konner, MJ (2001) Excellent introductions to evolutionary psychology include Konner, MJ (2001) The Tangled Wing: Biological Constraints on the Human Spirit The Tangled Wing: Biological Constraints on the Human Spirit. W. H. Freeman and Company, New York, NY; Barkow, JH, Cosmides, L, Tooby, J (1997) The Adapted Mind: Evolutionary Psychology and the Generation of Culture The Adapted Mind: Evolutionary Psychology and the Generation of Culture. Oxford University Press, Oxford, England; Buss, DM (1998) Evolutionary Psychology: The New Science of Mind Evolutionary Psychology: The New Science of Mind. Pearson Allyn and Bacon, New York, NY; Pinker, S (1999) How the Mind Works How the Mind Works. W. W. Norton and Company, New York, NY.

7 Pleasure, as we shall see Pleasure, as we shall see Cabanac, M (1992) Pleasure: the common currency. Cabanac, M (1992) Pleasure: the common currency. Journal of Theoretical Biology Journal of Theoretical Biology 155, no.2: 173-200. 155, no.2: 173-200.

7 Such biases persist Such biases persist A positive reinforcer is a stimulus that serves to increase the likelihood of the behavior that produces it. A positive reinforcer is a stimulus that serves to increase the likelihood of the behavior that produces it.

2 How to Win Friends and Influence People 12 In his book In his book The Language Instinct Pinker, S (1994) The Language Instinct Pinker, S (1994) The Language Instinct The Language Instinct. Perennial, New York, NY.

14 Such increasingly complicated Such increasingly complicated Humphrey, N (1992) Humphrey, N (1992) A History of the Mind A History of the Mind. Simon and Schuster, New York, NY; Mithen, S (1996) The Prehistory of the Mind:The Cognitive Origins of Art, Religion, and Science The Prehistory of the Mind:The Cognitive Origins of Art, Religion, and Science. Thames and Hudson, England; Klein, RG (2002) The Dawn of Human Culture The Dawn of Human Culture. John Wiley and Sons, New York, NY.

16 Many scholars agree Many scholars agree Diamond, JM (1992) Diamond, JM (1992) The Third Chimpanzee:The Evolution and Future of the Human Animal The Third Chimpanzee:The Evolution and Future of the Human Animal. Harper Collins, New York, NY; Deacon, T (1997) The Symbolic Species The Symbolic Species. W. W. Norton, New York, NY.

17 In cognitive science circles In cognitive science circles For a recent review of the representation problem, see Pylyshyn, ZW (2002) Mental imagery: in search of a theory. For a recent review of the representation problem, see Pylyshyn, ZW (2002) Mental imagery: in search of a theory. Behavioral Brain Sciences Behavioral Brain Sciences 25, no.2: 157-182. 25, no.2: 157-182.

17 But this is premature But this is premature Example used by Hauser, MD (2000) Example used by Hauser, MD (2000) Wild Minds:What Animals Really Think Wild Minds:What Animals Really Think. Henry Holt and Company, New York.

18 How did proto-emotions How did proto-emotions See Dunbar, R (1998) See Dunbar, R (1998) Grooming, Gossip, and the Evolution of Language Grooming, Gossip, and the Evolution of Language. Harvard University Press, Cambridge, MA; Deacon, T (1997) The Symbolic Species The Symbolic Species. W. W. Norton, New York, NY; Pinker, The Language Instinct The Language Instinct.

18 We will employ a more modern We will employ a more modern See Striedter, GF (1998) Progress in the study of brain evolution: from speculative theories to testable hypotheses. See Striedter, GF (1998) Progress in the study of brain evolution: from speculative theories to testable hypotheses. The Anatomical Record (New Anatomy), The Anatomical Record (New Anatomy), 253: 105-112; and relevant chapters in Gould, SJ (2002) 253: 105-112; and relevant chapters in Gould, SJ (2002) The Structure of Evolutionary Theory The Structure of Evolutionary Theory. Harvard University Press, Cambridge, MA.

18 "The human race began to talk "The human race began to talk Cited in Locke, Cited in Locke, The Child's Path to Spoken Language The Child's Path to Spoken Language.

20 In humans this exchange In humans this exchange For a review, see ibid.; Owens, RE (2000) For a review, see ibid.; Owens, RE (2000) Language Development: An Introduction Language Development: An Introduction. Pearson Allyn and Bacon, New York, NY.

20 Detailed experiments following Detailed experiments following Stern, DN, Spieker, S, Barnett, RK, MacKain, K (1983) The prosody of maternal speech: infant age and context related changes. Stern, DN, Spieker, S, Barnett, RK, MacKain, K (1983) The prosody of maternal speech: infant age and context related changes. Journal of Child and Language, Journal of Child and Language, 10(1): 1-15; Halle, PA, de Boysson-Bardies, B, Vihman, MM (1991) Beginnings of prosodic organization: intonation and duration patterns of disyllables produced by j.a.panese and French infants. 10(1): 1-15; Halle, PA, de Boysson-Bardies, B, Vihman, MM (1991) Beginnings of prosodic organization: intonation and duration patterns of disyllables produced by j.a.panese and French infants. Language and Speech, Language and Speech, 34, 299-318. 34, 299-318.

20 "Communication is successful" "Communication is successful" See Locke, See Locke, The Child's Path to Spoken Language The Child's Path to Spoken Language.

22 For instance, synthesized sounds For instance, synthesized sounds Murray, IR,Arnott, JL (1993) Toward the simulation of emotion in synthetic speech: a review of the literature on human vocal emotion. Murray, IR,Arnott, JL (1993) Toward the simulation of emotion in synthetic speech: a review of the literature on human vocal emotion. Journal of the Acoustical Society of America, Journal of the Acoustical Society of America, 93(2): 1097-108; Collier,WG, Hubbard,TL (2001) Musical scales and evaluations of happiness and awkwardness: effects of pitch, direction, and scale mode. 93(2): 1097-108; Collier,WG, Hubbard,TL (2001) Musical scales and evaluations of happiness and awkwardness: effects of pitch, direction, and scale mode. American Journal of Psychology, American Journal of Psychology, 114(3): 355-375. 114(3): 355-375.

22 Developmental psychologist Andrew Meltzoff Developmental psychologist Andrew Meltzoff For an overview of these experiments see Gopnick,A, Meltzoff,AN, Kuhl, PK (1999) For an overview of these experiments see Gopnick,A, Meltzoff,AN, Kuhl, PK (1999) The Scientist in the Crib: Minds, Brains, and How Children Learn The Scientist in the Crib: Minds, Brains, and How Children Learn. William Morrow, New York.

23 Studies have also shown that infants Studies have also shown that infants For a recent review of this literature see Turati, C, Simion, F, Milani, I, Umilta, C (2002) Newborns' preference for faces: what is crucial? For a recent review of this literature see Turati, C, Simion, F, Milani, I, Umilta, C (2002) Newborns' preference for faces: what is crucial? Developmental Psychology, Developmental Psychology, 38(6): 875-882. 38(6): 875-882.

3 What Makes Sammy Dance?

26 By the time he was twenty-four years old By the time he was twenty-four years old Published reports of case studies typically use a patient's initials or some other descriptor in an effort to maintain their anonymity. Heath, RG (1972) Pleasure and brain activity in man. Deep and surface electroencephalograms during o.r.g.a.s.m. Published reports of case studies typically use a patient's initials or some other descriptor in an effort to maintain their anonymity. Heath, RG (1972) Pleasure and brain activity in man. Deep and surface electroencephalograms during o.r.g.a.s.m. Journal of Nervous Mental Disorders, Journal of Nervous Mental Disorders, 154(1): 3-18. 154(1): 3-18.

26 Impressed by the work of Olds Impressed by the work of Olds Olds, J, Milner, P (1954) Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. Olds, J, Milner, P (1954) Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. Journal of Comparative Physiology and Psychology, Journal of Comparative Physiology and Psychology, 47(6): 419-427. 47(6): 419-427.

26 "They function in an almost continuous "They function in an almost continuous Quoted in Hooper, J,Teresi, D (1986) Quoted in Hooper, J,Teresi, D (1986) The Three-Pound Universe The Three-Pound Universe. Macmillan Publis.h.i.+ng Company, New York.

26 Electrodes and cannulas Electrodes and cannulas Olds, J, Milner, P (1954) Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. Olds, J, Milner, P (1954) Positive reinforcement produced by electrical stimulation of septal area and other regions of rat brain. Journal of Comparative Physiology and Psychology, Journal of Comparative Physiology and Psychology, 47(6): 419-427. 47(6): 419-427.

29 In the fifty years since In the fifty years since For recent reviews see Berridge, KC (2002) Pleasure of the brain. For recent reviews see Berridge, KC (2002) Pleasure of the brain. Brain and Cognition, Brain and Cognition, 52(1): 106-128; Wise, RA (2002) Brain reward circuitry: insights from unsensed incentives. 52(1): 106-128; Wise, RA (2002) Brain reward circuitry: insights from unsensed incentives. Neuron, Neuron, 36(2): 229-240; Kelley, AE, Berridge, KC (2002) The neuroscience of natural rewards: relevance to addictive drugs. 36(2): 229-240; Kelley, AE, Berridge, KC (2002) The neuroscience of natural rewards: relevance to addictive drugs. Journal of Neuroscience, Journal of Neuroscience, 22(9): 3312-3320. 22(9): 3312-3320.

29 As the circuit continued As the circuit continued Olds, J (1976) Brain stimulation and the motivation of behavior. Olds, J (1976) Brain stimulation and the motivation of behavior. Progress in Brain Research, Progress in Brain Research, 45: 401-426; Berridge, KC (2002) Pleasure of the brain. 45: 401-426; Berridge, KC (2002) Pleasure of the brain. Brain and Cognition, Brain and Cognition, 52(1), 106-128; Wise, RA (2002) Brain reward circuitry: insights from unsensed incentives. 52(1), 106-128; Wise, RA (2002) Brain reward circuitry: insights from unsensed incentives. Neuron, Neuron, 36(2): 229-240; Kelley, AE, Berridge, KC (2002) The neuroscience of natural rewards: relevance to addictive drugs. 36(2): 229-240; Kelley, AE, Berridge, KC (2002) The neuroscience of natural rewards: relevance to addictive drugs. Journal of Neuroscience, Journal of Neuroscience, 22(9): 3312-3320. 22(9): 3312-3320.

30 Behavioral scientists have used Behavioral scientists have used Woodward, DJ, Chang, JY, Janak, P, Azarov, A, Anstrom, K (2000) Activity patterns in mesolimbic regions in rats during operant tasks for reward. Woodward, DJ, Chang, JY, Janak, P, Azarov, A, Anstrom, K (2000) Activity patterns in mesolimbic regions in rats during operant tasks for reward. Progress in Brain Research, Progress in Brain Research, 126: 303-322. 126: 303-322.

31 Understanding how a.s.sociative learning Understanding how a.s.sociative learning For examples see Eichenbaum, H (2001) The hippocampus and declarative memory: cognitive mechanisms and neural codes. For examples see Eichenbaum, H (2001) The hippocampus and declarative memory: cognitive mechanisms and neural codes. Behavioral Brain Research, Behavioral Brain Research, 127(1-2): 199-207; Ha.s.selmo, ME, McClelland, JL (1999) Neural models of memory. 127(1-2): 199-207; Ha.s.selmo, ME, McClelland, JL (1999) Neural models of memory. Current Opinion in Neurobiology, Current Opinion in Neurobiology, 9(2): 184-188; Wallenstein, GV, Eichenbaum, H, Ha.s.selmo, ME (1998) The hippocampus as an a.s.sociator of discontiguous events. 9(2): 184-188; Wallenstein, GV, Eichenbaum, H, Ha.s.selmo, ME (1998) The hippocampus as an a.s.sociator of discontiguous events. Trends in Neuroscience, Trends in Neuroscience, 21(8): 317-323; Kesner, RP, Gilbert, PE,Wallenstein, GV (2000) Testing neural network models of memory with behavioral experiments. 21(8): 317-323; Kesner, RP, Gilbert, PE,Wallenstein, GV (2000) Testing neural network models of memory with behavioral experiments. Current Opinion in Neurobiology, Current Opinion in Neurobiology, 10(2): 260-265. 10(2): 260-265.

31 Rats often learn to avoid Rats often learn to avoid Parker, LA (2003) Taste avoidance and taste aversion: evidence for two different processes. Parker, LA (2003) Taste avoidance and taste aversion: evidence for two different processes. Learning and Behavior, Learning and Behavior, 31(2): 165-172; Maren, S (2001) Neurobiology of Pavlovian fear conditioning. 31(2): 165-172; Maren, S (2001) Neurobiology of Pavlovian fear conditioning. Annual Review of Neuroscience, Annual Review of Neuroscience, 24: 897-931. 24: 897-931.

32 "The dancing chicken is exhibiting" "The dancing chicken is exhibiting" Breland, K, Breland, M (1961) The misbehavior of organisms. Breland, K, Breland, M (1961) The misbehavior of organisms. American Psychologist, American Psychologist, 16: 681-684. 16: 681-684.

32 In fact, sugars rated In fact, sugars rated Sclafani, A, Fanizza, LJ, Azzara,AV (1999) Conditioned flavor avoidance, preference, and indifference produced by intragastric infusions of galactose, glucose, and fructose in rats. Sclafani, A, Fanizza, LJ, Azzara,AV (1999) Conditioned flavor avoidance, preference, and indifference produced by intragastric infusions of galactose, glucose, and fructose in rats. Physiology and Behavior, Physiology and Behavior, 67(2): 227-234. 67(2): 227-234.

37 Others are activated by stress, learning Others are activated by stress, learning For a review see Wallenstein, GV (2003) For a review see Wallenstein, GV (2003) Mind, Stress, and Emotions: The New Science of Mood Mind, Stress, and Emotions: The New Science of Mood. Commonwealth Press, Boston.

43 At present, there are several controversial At present, there are several controversial Slezak, M, Pfrieger, FW (2003) New roles for astrocytes: regulation of CNS synaptogenesis. Slezak, M, Pfrieger, FW (2003) New roles for astrocytes: regulation of CNS synaptogenesis. Trends in Neuroscience, Trends in Neuroscience, 26(10): 531-535;Adams, P, c.o.x, K (2002) A new interpretation of thalamocortical circuitry. 26(10): 531-535;Adams, P, c.o.x, K (2002) A new interpretation of thalamocortical circuitry. Philosophical Transactions of the Royal Society of London B Biological Sciences, Philosophical Transactions of the Royal Society of London B Biological Sciences, 357(1428): 1767-1779; Grossman,AW, Churchill, JD, Bates, KE, Kleim, JA, Greenough, WT (2002) A brain adaptation view of plasticity: is synaptic plasticity an overly limited concept? 357(1428): 1767-1779; Grossman,AW, Churchill, JD, Bates, KE, Kleim, JA, Greenough, WT (2002) A brain adaptation view of plasticity: is synaptic plasticity an overly limited concept? Progress in Brain Research, Progress in Brain Research, 138: 91-108. 138: 91-108.

46 From culture to culture From culture to culture Sugarman, L (2001) Sugarman, L (2001) Lifespan Development: Theories, Concepts and Interventions Lifespan Development: Theories, Concepts and Interventions. Psychology Press, New York.

4 The Pleasure of Touch 49 By the time the world met him By the time the world met him Ruckel, I (2002) Ruckel, I (2002) Abandoned for Life: The Incredible Story of One Romanian Orphan Abandoned for Life: The Incredible Story of One Romanian Orphan. JB Information Station Publishers, St. Louis.

50 As late as 1915 As late as 1915 Chapin, HD (1915) A plea for accurate statistics in children's inst.i.tutions. Chapin, HD (1915) A plea for accurate statistics in children's inst.i.tutions. Transactions of the American Pediatric Society, Transactions of the American Pediatric Society, 27: 180. 27: 180.

50 It is important to note It is important to note Holt, LE (1935) Holt, LE (1935) The Care and Feeding of Children The Care and Feeding of Children (15th edition). Appleton-Century, New York. (15th edition). Appleton-Century, New York.

51 The pediatric wards of the famed Bellevue The pediatric wards of the famed Bellevue Brennemann, J (1932) The infant ward. Brennemann, J (1932) The infant ward. American Journal of Diseases of Children, American Journal of Diseases of Children, 43: 577. 43: 577.

51 "If they continued hurting themselves "If they continued hurting themselves Ruckel, I (2002) Ruckel, I (2002) Abandoned for Life: The Incredible Story of One Romanian Orphan Abandoned for Life: The Incredible Story of One Romanian Orphan. JB Information Station Publishers, St. Louis.

53 For touch to be perceived For touch to be perceived Falk, D, Gibson, KR (2001) Falk, D, Gibson, KR (2001) Evolutionary Anatomy of the Primate Cerebral Cortex Evolutionary Anatomy of the Primate Cerebral Cortex. Cambridge University Press, Cambridge, England.

53 Each of these sensory modalities Each of these sensory modalities For a general review of the touch system, see Rowe, MJ, Iwamura, Y (2000) For a general review of the touch system, see Rowe, MJ, Iwamura, Y (2000) Somatosensory Processing: From Single Neuron to Brain Imaging Somatosensory Processing: From Single Neuron to Brain Imaging. Taylor & Francis, New York.

54 A very active area of research A very active area of research Fox, K, Glazewski, S, Schulze, S (2000) Plasticity and stability of somatosensory maps in thalamus and cortex. Fox, K, Glazewski, S, Schulze, S (2000) Plasticity and stability of somatosensory maps in thalamus and cortex. Current Opinion in Neurobiology, Current Opinion in Neurobiology, 10(4): 494-497; Jones, EG (2000) Cortical and subcortical contributions to activity-dependent plasticity in primate somatosensory cortex. 10(4): 494-497; Jones, EG (2000) Cortical and subcortical contributions to activity-dependent plasticity in primate somatosensory cortex. Annual Review of Neuroscience, Annual Review of Neuroscience, 23: 1-37; Rauschecker, JP (2002) Cortical map plasticity in animals and humans. 23: 1-37; Rauschecker, JP (2002) Cortical map plasticity in animals and humans. Progress in Brain Research, Progress in Brain Research, 138:73-88. 138:73-88.

54 Psychologist William Greenough Psychologist William Greenough Klintsova, AY, Greenough, WT (1999) Synaptic plasticity in cortical systems. Klintsova, AY, Greenough, WT (1999) Synaptic plasticity in cortical systems. Current Opinion in Neurobiology, Current Opinion in Neurobiology, 9(2): 203-208; Greenough, WT (1987) Mechanisms of behaviorally-elicited and electrically-elicited long-term potentiation. 9(2): 203-208; Greenough, WT (1987) Mechanisms of behaviorally-elicited and electrically-elicited long-term potentiation. International Journal of Neurology, International Journal of Neurology, 21: 137-144. 21: 137-144.