Placebo: Mind over Matter in Modern Medicine. Dylan Evans
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.