Читать книгу Sex, Drugs and Chocolate: The Science of Pleasure - Paul Martin - Страница 5

Pleasure is the only thing worth having a theory about.

OSCAR WILDE,

The Picture of Dorian Gray (1891)

What is pleasure for? That is the sort of question biologists ask. What they mean is: how did this feature of our biological makeup help our ancestors to survive and reproduce, and therefore to become our ancestors? To put it another way, why did evolution equip us and other animals with the capacity and appetite to experience pleasure in so many varied and delightful ways, including perhaps some that are still undiscovered?

The simplest answer is that pleasure and its dark counterpart, pain, are there to encourage us to do the right things. Pleasure entices us to behave in ways that are likely to be biologically beneficial, while pain discourages us from doing ourselves harm. The ever-shifting balance between pleasure and pain is, to quote the philosopher David Hume, ‘the chief spring or actuating principle of the human mind’.

The idea that pleasure and pain direct our behaviour has been circulating in various guises for thousands of years, dating back at least as far as Epicurus and like-minded philosophers of ancient Greece. Psychology, as it came to be known, built upon this simple concept in the nineteenth century. In 1880, for example, Herbert Spencer advanced a specific psychological theory that all human behaviour is underpinned by the twin motivating forces of pleasure and pain.¹

Sigmund Freud pursued the theme with his psychoanalytic Pleasure Principle. In his characteristically doubt-free style, Freud asserted that he had no hesitation in assuming that all mental activity was ‘automatically regulated’ by the Pleasure Principle – by which he meant that all mental activity was directed towards the production of pleasure or the avoidance of displeasure. Freud decided that pleasure and displeasure were reflections of a mental phenomenon that he called ‘unbound excitation’; pleasure supposedly acted to reduce this excitation, while displeasure did the reverse. In another of his works, an even less hesitant Freud proclaimed that ‘It is simply the programme of the pleasure principle that determines the purpose of life.’

What has science, as distinct from Freudian conjecture, revealed about pleasure? One basic conclusion is that the behaviour of humans and other animals is self-evidently motivated by stimuli that are associated with pleasure. Pleasurable rewards (or ‘reinforcers’) tend to increase the frequency of the behaviour that produced them, whereas unpleasant stimuli do the reverse. The long-suffering experimental pigeon will peck energetically at a button if its efforts are rewarded with food, but it will rapidly stop pecking and avoid the button if instead it receives a mild electric shock.

A second basic conclusion is that the sorts of activities we find pleasurable could mostly be viewed as biologically beneficial, in the sense that they would generally have helped our ancestors to survive and reproduce in their natural environment. As we saw earlier, people consistently report that socialising, having sex and eating are their main sources of pleasure. These activities are also biologically beneficial, in the right circumstances. Even the simplest pleasures of life, like warming yourself in front of a fire or tending a garden, make good biological sense if you imagine yourself as one of your hunter – gatherer ancestors.

The capacity to respond to pleasurable stimuli emerged very early in evolution and is detectable, in one form or another, in animals ranging from flies and shellfish to dogs and gorillas. Pleasure almost certainly plays a bigger role in the lives of other species than we humans often tend to assume. The neuroscientist Jaak Panksepp has even uncovered evidence that rats are capable of experiencing playful joy which they express in the form of high-pitched ‘laughing’. When a rat has a joyful experience, such as playing with another rat, it emits a series of ultrasonic (50-kilohertz) chirps. Panksepp contends that these vocalisations are biologically related to the joyful laughter that children emit when they are playing. The thought that rats enjoy a giggle with their mates is a reminder that life for other species can amount to more than just a grim struggle for survival.

If pleasure did evolve to guide our behaviour, then how does it perform this biological function? The task is not quite as straightforward as it might seem. At any given moment we could be doing many different but mutually exclusive things, each of which would be biologically beneficial. We might, for example, be faced with the choice of cooking dinner, sleeping in a cosy bed or having vigorous sex. How do we decide what to do next? Humans and other animals must continually choose between competing requirements. We therefore require some form of mechanism for weighing the conflicting motivations against each other and choosing the best option at the time. To help us choose, we need some form of measuring stick or common currency. According to the physiologist Michel Cabanac, that common currency is pleasure.

The essence of Cabanac’s theory is that pleasure enables the brain to compare the strengths of current motivations to perform different activities. When choosing between, say, eating, staying warm or avoiding danger, we may, of course, make a conscious, rational judgement about our priorities. But even an apparently conscious decision will be influenced by an unconscious weighing of the options in terms of how much pleasure or displeasure each would produce. We are drawn towards the most pleasant, or least unpleasant, course of action. This simple form of hedonism encourages us to behave in ways that, on average, will be in our best biological interest.

Pleasure is the hidden force behind what might be called ‘gut instinct’; it guides our choices even when we think we are using our conscious mind to make rational decisions. Experimental tests have lent support to this simple theory, confirming that humans and other animals behave in line with its detailed predictions. We make unconscious but surprisingly precise trade-offs between the amount of displeasure we are prepared to experience and the amount of pleasure we anticipate in return. The evidence suggests that something akin to pleasure is used to prioritise actions in other species as well. Even a lizard will be guided by the unconscious trade-off between, say, physical discomfort and the attractiveness of food.

If evolution has equipped us with pleasure as a mechanism to help guide our behaviour then we would expect those feelings of pleasure to be inherently transient and self-limiting. Faced with competing priorities, we will choose the most pleasant or the least unpleasant course of action. But in order to survive and thrive, we must stop performing that activity and switch to something else as soon as our current needs have been satisfied and other priorities have risen to the fore. If a pleasurable activity continued to be pleasurable for too long, we would be in danger of getting locked into doing it and therefore neglecting higher-priority needs. Our ancestors would not have survived long enough to become our ancestors if they had sunk into a state of enduring bliss every time they did something enjoyable. For pleasure to do its biological job as a motivational common currency, it must be short-lived. And so it is.

Everyday experience, backed up by a reassuring mass of experimental data, confirms that pleasure is indeed short-lived. We habituate quite rapidly to pleasurable sensations. No matter how earth-shaking it may be at the time, any given pleasure will fade and the moment will pass. William Shakespeare famously encapsulated this aspect of human nature in the opening lines of Twelfth Night:

If music be the food of love, play on;

Give me excess of it, that, surfeiting,

The appetite may sicken, and so die.

The ephemeral nature of pleasure has important practical implications, which we will explore later. Above all, it means that anyone who attempts to rely exclusively on pleasure to make them happy is likely to have a struggle on their hands. The present pleasures will inevitably dwindle, forcing the determined hedonist to keep increasing the dosage or switch to new ones. Socrates likened pleasure-seekers to the damned in Hell, who are condemned for ever to keep trying to fill leaky jars. Psychologists refer to this phenomenon as the hedonic treadmill.

Pleasure must be self-limiting to do its job. However, biological reasoning would suggest that displeasure and pain should not be self-limiting in the same way. Instead, they should persist for as long as the problem that gives rise to them. If the biological function of displeasure and pain is to protect us from harm, we would expect them to linger until the corresponding threat to our well-being has gone away. Again, the theory is borne out by reality. Unpleasant feelings such as anxiety, fear and pain are generally not as ephemeral as pleasure; we do eventually adjust to displeasure or pain, but more slowly and less completely than in the case of pleasure. As the essayist William Hazlitt put it, ‘pain is a bittersweet, which never surfeits’.

The simple idea that pleasure evolved to make us behave in biologically beneficial ways further implies that there should be a clear relationship between our current biological needs and our current experience of pleasure. As those needs change, so too should our response to pleasurable stimuli. Once again, the theory is in line with everyday reality and experimental evidence. Our response to potentially pleasurable stimuli does indeed vary according to our current internal state and needs. Drinking tepid, murky water from a chipped mug can be delightful when you have a raging thirst, but not otherwise. Similarly, sinking into a steaming hot bath is altogether more pleasant when you are cold and wet than it is after a day of sunbathing on a tropical beach. Experimental studies have confirmed that changes in our internal state affect the amount of pleasure or displeasure we experience in response to stimuli. In one typical experiment, hungry people were repeatedly given drinks of sugary water, which they had to spit out without swallowing. They continued to find the sweet taste pleasant each time they experienced it. But if, instead, they swallowed each drink when it arrived, the sweet taste became progressively more unpleasant. Sweet pleasure turned to cloying displeasure as their stomach filled with sugary liquid. The same physical stimulus could elicit pleasure or displeasure, depending on the individual’s current internal state.

The idea that pleasure and other emotions are reflections of our body’s physical state has a long pedigree. William James, the pioneering nineteenth-century psychologist (and brother of writer Henry), proposed that our emotions arise, at least in part, from an awareness of our physical reactions to stimuli.² So, for example, we feel afraid because we have become aware that our heart is pounding and our hands are trembling, rather than the other way round. James realised that if emotions are linked to internal state then we might be able to alter our emotions by manipulating the signals reaching the brain from the rest of the body. He tested this hypothesis with a very simple experiment. He smiled. More specifically, he forced his facial muscles to form the shape of a smile, even though he did not feel in the mood for smiling. (William James suffered from depression – hence, perhaps, his particular attraction to smiling.) He found that the more he smiled, the jollier he felt. The physical act of smiling was enough to elicit the corresponding emotional state, as though the configuration of his facial muscles had somehow tricked his brain into believing that he must be feeling good.

The two-way relationship between facial expression and emotion has been substantiated by more systematic experiments. In one study, psychologists got people to hold a pencil between their teeth without it touching their lips. This made them smile, without being consciously aware of doing so. As William James would have predicted, the physical act of smiling lifted their subjective mood, even though the subjects did not know they were smiling. By comparison, sucking a pencil with their lips wrapped around it did nothing to lift their mood. Similar mood-enhancing effects have been produced by giving experimental volunteers detailed instructions to move particular muscles in their face, causing them unwittingly to smile. The effect is strongest when the smile is of the so-called Duchenne variety – the ‘genuine’ type of smile that involves the corners of the eyes as well as the mouth. One day, perhaps, the well-read pleasure-seekers among us will be recognisable from the tell-tale pencil clenched between their teeth.

Deliberately smiling really can lift your mood. Try it for yourself. Use a pencil if you must. So too can holding your head high or whistling a happy tune. In each case, a physical act that would normally reflect an underlying emotional state can also elicit that same emotional state. Of course, people who never stop smiling can irritate those of us in a less ebullient mood, especially if their smile is obviously fake. Some celebrities develop a permanent rictus, which can vary from self-satisfied to borderline psychopathic. Nonetheless, they are on to something. Even a fake smile can make us feel a bit better, because the feedback from the facial muscles tells the brain that something good must be happening. The feel-good factor is reinforced if the smile evokes friendly responses from other people. The idea that emotions reflect some sort of mental map of the body’s internal state is further supported by brain-scanning studies, which show that pleasure and other emotions are accompanied by activity in parts of the brain that are known to be involved in monitoring the body’s internal state.³

At first sight, then, it might appear as though we have cracked the scientific puzzle of pleasure at an awkwardly early stage in this book. According to the simple theory just outlined, activities that are generally good for us are pleasurable and that is why we keep doing them. Pleasure is the brain’s universal currency, which it uses to compare different behavioural options. We plump for the activity that is likely to produce the most pleasure or the least displeasure, having unconsciously taken account of our current biological needs. If this explanation seems too simple, that is because it is too simple.

A moment’s thought will reveal some obvious gaps in this crude model of pleasure. For a start, we clearly are not just slaves to instant gratification. Much of what we and other animals do is guided by our expectations about future rewards, rather than the immediate consequences of our actions. We frequently choose to do things that are unpleasant or even painful in the short term in order to pursue broader or longer-term goals. Getting out of bed and going to work in the morning is a common example. Giving birth and having cosmetic surgery are others. When everything else is equal, we prefer pleasurable activities over unpleasant ones. In the real world, however, everything else seldom is equal. Our behaviour is shaped by context, expectations and a host of other factors.

Even young children can choose to forgo immediate pleasure in order to obtain a larger reward later. This ability, which is known as delay of gratification, is correlated with happiness and intelligence. One long-term study found that the four-year-old children who performed best in a laboratory test of their ability to delay gratification subsequently developed into more socially competent adolescents who did better at school and coped better with stress. Other apes also have the capacity to delay gratification. Chimpanzees were able to demonstrate it in an experiment in which they were given morsels of chocolate. Twenty chocolates were placed, one by one, in front of the chimpanzee over the course of a few minutes. The animal could eat the accumulated chocolates at any stage, but as soon as it ate any it would receive no more. If, on the other hand, it contained its desire, it was allowed to eat all twenty pieces at the end. Chimpanzees adore chocolate, as any highly intelligent being would. Nonetheless, they proved quite capable of resisting the lure of immediate gratification in order to win a bigger chocolaty reward later.

Much of what we might think of as pleasure is actually the anticipation of pleasure or the desire for something we believe will be pleasurable. Charles Darwin highlighted this distinction in The Expression of the Emotions in Man and Animals, published in 1872. He noted that humans and other animals often express feelings of pleasure in the form of movements and sounds – as, for example, when young children laugh, clap their hands and jump for joy. However, Darwin observed that:

It is chiefly the anticipation of a pleasure, and not its actual enjoyment, which leads to purposeless and extravagant movements of the body, and to the utterance of various sounds. We see this in our children when they expect any great pleasure or treat; and dogs, which have been bounding about at the sight of a plate of food, when they get it do not show their delight by any outward sign, not even by wagging their tails.

Freud also recognised that there is more to human motivation than the simple principle of seeking pleasure and avoiding pain in the here and now. In a later work entitled Beyond the Pleasure Principle, he wrote: ‘The most that can be said is that there exists in the mind a strong tendency towards the pleasure principle, but that that tendency is opposed by certain other forces or circumstances, so that the final outcome cannot always be in harmony with the tendency towards pleasure.’ Recognising the anticipatory nature of human motivation, Freud described it as ‘hedonism of the future’.

Another embarrassing flaw in the simple pleasure principle is that many of us spend surprisingly little of our time doing the things that actually give us the most pleasure. This is why most people feel significantly better if they deliberately make themselves spend more time doing pleasant things. Several psychological studies have demonstrated that instructing people to adopt a conscious strategy of engaging more in pleasant activities really does lift their mood, even if they were not depressed to begin with. ‘Pleasant activities training’, as it is called, is demonstrably more effective at raising mood than physical fitness training or daily sessions of introspection. Now, you might regard the revelation that doing nice things makes people feel better as a statement of the blindingly obvious. What is less obvious, however, is why most of us do not already behave in this way. If our behaviour really were driven by the simple pleasure principle of doing what feels good now, our lives should already be crammed full with pleasurable activities. The fact that this is not generally the case is further proof that the truth is more complex.

The simple pleasure principle is clearly not sufficient to explain the intricate reality of human and animal behaviour. We will see later that much of what we do is driven not by pleasure but by desire. Meanwhile, let us take a closer look at the trio responsible for so much of human pleasure: sex, drugs and chocolate.