Czytaj książkę: «Placebo: Mind over Matter in Modern Medicine»

PREFACE

‘What we are today comes from our thoughts of yesterday, and our present thoughts build our life of tomorrow: our life is the creation of our mind.’¹ The opening words of the Dhammapada, one of the most revered Buddhist scriptures, articulate an ancient and pervasive idea – the mind is all-powerful, and no element of physical reality is beyond its reach. In the West, too, the supremacy of mind over matter is championed by religious movements old and new. Christians and New Age devotees alike agree that the blind can be made to see, and invalids be made to walk, by the power of faith alone.

Science tells a rather different story. The power of the mind, it says, is strictly limited. Every effect it has on the world beyond the body must pass through the prosaic and puny conduit of muscle-power. The victim of total paralysis is completely impotent, his mind entombed, as the medical term – ‘locked-in syndrome’ – makes painfully clear. Except for the single flutter of an eyelid, which may be the only muscle to remain under voluntary control, the paralytic has no way of influencing the world around him.

But what of the world within? Even science recognises that the brain governs more than the muscles. The discovery, in the 1980s, of the rich supply of nerves linking the brain with the immune system led to the rise of a new branch of medical research known as psychoneuroimmunology (PNI). Advances in PNI have raised hopes that the powers of the mind may not be quite as impoverished as most scientists have thought. Telekinesis and extra-sensory perception may be forever alien to the scientific worldview, but perhaps scientists need not be so pessimistic when it comes to the mind’s capacity to influence events within one’s own body. Walking on water may be out of the question, but maybe – just maybe – science might discover that disease can be cured by thought alone. Will science, having exposed so many magical powers as mere fantasies, at least allow this one to stand? The heavens have been lost to Copernicus, and creation has been vanquished by Darwin. But the soul, perhaps, still lurks in the healing power of the mind.

That phrase – ‘the healing power of the mind’ – could cover a multitude of sins. Many sorts of phenomena might fall under its umbrella. Relaxation, for example, lowers blood pressure and may reduce the risk of coronary heart disease. There is nothing particularly magical about that, however. This book is about something much stranger – the possibility of a direct effect of belief on the body, an effect that is not achieved by means of any muscle, not even by the muscles that control our breathing.

Some of the apparent strangeness of the belief effect is almost certainly due to the ethereal images that are still conjured up in many people’s imaginations by the term ‘mind’. Despite the amazing scientific advances that have transformed our understanding of the brain during the past few decades, it is still common to find people speaking about the mind as if it were something completely separate from the body. While this manner of speaking is thousands of years old, it was most influentially given expression almost four centuries ago by the French philosopher René Descartes (1596–1650). Descartes argued that minds and bodies were composed of completely different kinds of substance – one spiritual in nature, the other material. Given this starting point, it is hard indeed to see how minds can affect bodies, or how bodies can affect minds. And yet they clearly do affect each other. Before I typed this sentence out on the keyboard of my computer, the words formed in my mind; when my fingers then struck the keys, their movement was yet another mundane example of the power of mind over matter. Likewise, if my mood improves after sipping a glass of wine, this is an equally familiar case of the body affecting the mind.

Descartes proposed a rather bizarre theory to explain how the mind and the body were able to communicate with one another. He claimed that a tiny structure in the brain known as the pineal gland acted as a kind of spiritual telephone, enabling messages to be sent back and forth between the ethereal mind and the material body. If that was really the case, of course, we would be able to turn people into mindless zombies simply by removing their pineal glands. Unfortunately for Descartes’ theory, however, people whose pineal glands are destroyed do not suddenly turn into zombies. In the centuries since Descartes, we have learned enough about the brain to know that the mind cannot be tied down to any particular part, such as the pineal gland. This is not because the mind uses lots of other regions of the brain to communicate with the body – it is because the mind is simply another name for the activity of the brain.

We know now that the processes of thinking and wishing that Descartes ascribed to the ethereal, invisible mind are, in fact, complex patterns of electro-chemical activity that swirl around in the lump of fatty tissue we call the brain. There is no need for any spiritual telephone to link the brain to the mind, because ‘the mind’ is just another name for what the brain does. This ‘astonishing hypothesis’ – as Nobel Prizewinner Francis Crick has called it – removes at one fell swoop a lot of the apparent mystery of that confusing phrase ‘the mind-body problem’. What is the problem, when the mind is simply the activity of one part of the body? The mystery turns out to be an artefact of our confused ways of speaking, such as our tendency to persist in talking about ‘mind over matter’, as if the mind were not itself a material process. If there is any problem at all, it is that of understanding how one part of the body – the brain – communicates with the rest.

In the early days of scientific psychology, at the end of the nineteenth century, there was a very simple picture of how the brain and the body communicated. First, certain bits of the body – the sensory organs, such as the eyes and ears – provided information to the brain via the sensory nerves. Then, after the brain had worked out what to do on the basis of this information, it passed the command on to the muscles by means of motor neurons. As our understanding of physiology and anatomy increased, however, it became clear that the situation was far more complex. For a start, the ‘five senses’ of vision, hearing, taste, touch and smell turned out to be much less monolithic than was previously thought. Touch, for example, is not a single process, but a combination of many different ones; various kinds of receptors in the skin are designed to detect different types of stimuli, such as heat, pressure and chemicals. Also, it has become clear that the brain does not just receive information from the outside world but also from a rich array of sensory nerves that permeate our internal organs. The information they convey to the brain is vital in co-ordinating many physiological processes, even though this information rarely becomes the object of conscious attention.

Still more exciting has been the discovery that some information about the internal state of the body is conveyed to the brain not via sensory nerves, but via chemicals in the bloodstream. Many of these molecular messengers are secreted by white blood cells, whose main role is to help the body fight infection. This has led some biologists to argue that the immune system is itself a kind of sensory organ.² Just as the eyes detect visual information about the outside world, so the various components of the immune system are continually monitoring the inside of our bodies for signs of infection, and alerting the brain when they discover them.

The discovery that we possess internal senses as well as external ones is paralleled by the finding that the motor neurons are not the only means by which the brain sends its messages back to the rest of the body. Besides telling the muscles how to move, the brain can also instruct immune cells to change their activity. Certain parts of the brain are designed to secrete certain chemicals back into the bloodstream, and some of these chemical messengers are picked up by white blood cells, which can alter their behaviour accordingly. As we learn more about the ways in which the brain communicates with the rest of the body, it is becoming clear that mental processes need not start with external perception and end in external movement. Some can originate and terminate in events deep inside the body.

It is to this process of internal communication between the brain and the body that I refer when I speak about the healing power of the mind, not to any miraculous Cartesian spiritual telephone. Yet my sense of wonder is undiminished. In my opinion, the scientific discoveries that have allowed us to glimpse the mechanisms that underlie the complex interactions between our beliefs and our health are even more fascinating than the more mystical talk about ‘energies’ and ‘auras’ that titillates some. And the scientific story does have one notable advantage that the mystical ones lack – it is based on fact rather than fiction.

Unfashionable as it may be to say so at a time of growing interest in alternative medicine and faith healing, the power of the mind to heal the body is entirely dependent on the various physical mechanisms just described. If there is no chemical messenger to act as a go-between, the brain is powerless to alter the action of the immune system. And even when such molecules do exist, they cannot endow the immune system with supernatural powers. All they can do is tell the immune system to behave in one way rather than another. If something is beyond the power of the immune system altogether, no amount of chemical messengers secreted by the brain will change this.

Rather than attempting to cover every conceivable avenue by which the mind might heal the body, from hypnosis to relaxation, I have chosen to focus on one particular phenomenon – the placebo response. The advantage of focusing on this process, rather than any other, is that science has something to say about it. While it is certainly possible that there are other processes that allow the mind to heal the body, next to nothing is known about them. This is not to say that scientists have a complete picture of the placebo response – far from it, in fact. But there is just about enough scientific research to enable some reasonably solid hypotheses to be developed and tested. And more data is accumulating, as more funds are increasingly devoted to elucidating the mechanisms that underlie the placebo response.

As we shall see in Chapter One, inert substances such as bread pills and salt water have long been used by doctors as sops to desperate patients. In the twentieth century, however, medical researchers began to suspect that placebos such as these might actually have real therapeutic effects. By the 1950s, it had become established medical wisdom that placebos could help to alleviate virtually any disease. More recently, researchers have unearthed significant flaws in this early research, leading some to doubt the very existence of the placebo response. Chapter Two sifts through the evidence to put together a picture of what placebos really can and can’t do. The interesting question is not whether placebos can alleviate medical problems – they can – but which medical problems they affect.

The list of medical conditions that respond to placebos is a rather odd one, without apparent rhyme or reason. Yet, as Chapter Three argues, there is in fact a single biological mechanism that is common to them all. If this mechanism is activated in all these medical conditions, it follows that placebos might work by turning this mechanism off. I may be wrong, and the placebo response may involve other mechanisms. If so, some of the predictions that follow from the model put forward here will not stand up to empirical test. That strikes me as a virtue rather than a disadvantage. Good theories, as the philosopher of science Karl Popper never tired of repeating, must be falsifiable. The bolder the conjectures, the more chances of being shown to be wrong, the better the theory. The theory put forward here is consistent with most, if not all, the data we currently have about the placebo response. But these are early days, and it is perfectly possible that scientists may discover further data that prove the theory wrong.

Such an event would not invalidate the whole book. Most of the arguments in its second half would still hold up even if the theory advanced in Chapter Three turns out to be wrong. Whatever the physiological details may be, for example, the important thing about placebos is that they cause their bodily effects indirectly, by means of causing some change in the mind. Chapter Four looks at the psychological element in the placebo response, the key mental event that triggers the physiological processes involved. I argue that this mental event is the formation of a belief – the belief that one has just received an effective medical treatment. Placebos are treatments that only work if you believe in them.

Chapter Five puts the physiological and psychological mechanisms in an evolutionary context. How and why did humans evolve in such a way that their minds can trick their bodies into healing themselves? When did this capacity first appear? Chapter Six examines the so-called ‘nocebo effect’ – the power of placebos to harm as well as to heal – and argues that this crude dichotomy into good and bad seriously misrepresents the complexity of the biological details. Since many symptoms turn out to be defence mechanisms activated by the body itself, it is much harder than one might think to decide whether or not a physiological process is pathological or beneficial.

Chapters Seven and Eight take a hard look at alternative medicine and psychotherapy, and ask whether or not these popular approaches to healing are really anything more than placebos. The question is especially important at a time when consumer demand for these products is high. Should we believe the hype surrounding acupuncture and homeopathy, or is the emperor naked?

Finally, Chapter Nine looks at the ethical questions raised by the use of placebos. To use a placebo knowingly, whether in medical practice or in clinical trials, it seems that doctors must deceive their patients. Can such deception ever be justified, or do doctors have an absolute duty to tell their patients the truth? And how do the emerging scientific discoveries discussed earlier in the book throw new light on this ancient dilemma?

That concludes the rough sketch of the terrain; now begins the journey.

Dylan Evans, Fairford, July 2002

PREFACE TO THE PAPERBACK EDITION

Since this book was first published, in January 2003, it has provoked a variety of responses, ranging from enthusiastic approval to cold hostility. This is probably to be expected, given that the book deals with a topic that is at the very edge of scientific discovery. Until we have gathered more evidence, scientists will continue to argue about the biological and psychological mechanisms that underlie the placebo response. Indeed, it is this process of argument and debate that makes science such a lively and passionate activity.

There are repeated reminders throughout the book that the theory proposed in Chapter 3 is not yet proven, but even this was not enough to prevent some critics from accusing me of presenting my hypothesis as if it were already an established fact. This is perhaps testimony to the reluctance of many medical scientists to venture beyond the safe realm of data and into the perilous terrain of theory. That reluctance is a shame, because speculation is essential if we are to discover anything new.

Recent research, published since this book was first published, appears to confirm the theory it proposes. Readers may find links to some of this research on my website (www.dylan.org.uk), which is regularly updated. But even if the theory proposed here turns out not to be a complete explanation of the placebo response, I am confident it will remain an important part of the puzzle. Read this book, and judge for yourself!

Dylan Evans, May 2003