Later studies by the American-born neurosurgeon Wilder Penfield in Montreal observed the response of conscious epilepsy patients to brain stimulation by electrodes. Penfield used the technique in order to plan brain surgery to relieve convulsions experienced in specific regions of the body. But what he obtained as a result was a new map of the brain. Penfield’s masterstroke was to employ an artist when he published his findings in 1937. Mrs H. P. Cantlie drew a ‘cortical homunculus’ in which the various sensory and motor functions of the body were depicted at a scale in proportion to the volume of the area of the brain thought to be responsible for their control. Unfortunately, the diagram – showing greatly enlarged thumbs and large fingers, hands and feet compared to the limbs and trunk of the body – looked a bit like a frog squashed on the road. More instructive and enduring is a later version that Penfield published in which the sensory and motor organs are draped directly around the hemispheres of the brain in a sectional view across the head. The lips and the thumb stand out especially. This graphic idea has taken root and inspired ever more grotesque variants since, as well as having its precursors in the homunculus of medieval belief, who was literally a little man, or ‘manikin’, a kind of Mini-Me that might be conjured by an alchemist or a magician. These distorted human figures are perhaps also imaginatively invoked in the gangly dragons and monsters of our nightmares and cartoons, with their grasping fingers and clumping feet.
True images of the brain are brought to us by a different magic. The secret is the phenomenon of nuclear magnetic resonance, a discovery of such momentous significance that it has been marked by the award of Nobel Prizes on six occasions: three in physics, two in chemistry, and the latest in medicine, awarded in 2003 for its application in the form of medical imaging now universally known as MRI.
I went to have my brain scanned more than twenty years ago. It was the spring of 1988, and this form of imaging had only just gained approval for clinical use. So new was the technique that nobody had yet thought to ditch the ‘nuclear’ part of the name that somehow failed to reassure prospective patients. I am not a patient, however, but writing an article for Popular Science magazine.
When I arrive at the Albany Medical Center in the New York state capital, the white-coated head of neuroradiology, Gary Wood, begins by asking me some preliminary questions. ‘Is there anything wrong with you? Do you have anything metal on you – pens, paper clips?’ I deposit keys, a pen, and my tape recorder in a locker. Then the doctor opens a big door shielded with copper and ushers me into the MRI room.
A large doughnut-shaped machine fills the room. It is emblazoned with the logo of General Electric, the company founded nearly 100 years before by Thomas Edison, funnily enough, and based in nearby Schenectady. Smoothly contoured white plastic conceals its five-tonne magnet. (Medical NMR magnets may generate magnetic fields measuring some 15,000 gauss; the Earth’s magnetic field by comparison averages just 0.5 gauss, while the magnet in your fridge door might produce around 50 gauss.) Wood’s assistant helps me on to a gurney that projects from the bore of the magnet, and then flicks a switch. Powered by hydraulics (motors won’t work near this huge magnet), I glide almost silently into the magnet until my head is positioned at its centre. Any sense of claustrophobia is mitigated by the mirror thoughtfully angled above my eyes so that I can see out beyond my feet and through the room’s observation window to where Gary and his colleagues are monitoring the scan. Through a two-way audio link, I hear them typing instructions into the computer and chatting excitedly about their new equipment. ‘Lie still,’ I am told. Gary presses a button. A rapid, dull drumming fills my ears, but I feel nothing as the massive machine scans the depths of my brain.
Afterwards, Gary shows me what he has recorded on the monitor. It is the first time I have been able to see inside my own body. Yet even at this early date, I find I am jaded by the generic familiarity of the images. ‘MRI has shifted our sense of transparency so that we can see those structures whose form and function had previously been the domain of poets and philosophers,’ I read in one rather awestruck history of medical imaging. But what is seeing? I am aware that what I am looking at is not a simple photograph, but a highly indirect image, a digital manifestation of a series of radio-frequency signals, which are themselves the product of tiny magnetic fields produced by hydrogen atoms in my brain in response to the massive input signal of the imaging machine. It seems to me the poets and philosophers might still have the edge.
Sensing my ambivalence, perhaps, Gary points to different shades of grey on the screen that represent the outer shell of my skull, my bone marrow, and even my cerebrospinal fluid. ‘Now we’re going to page through,’ he tells me. ‘We’re going to drive right through your head.’ A series of images appears on the screen as Gary chases my optic nerves from my eyes into my brain. He pauses at one picture, a cross-section clearly showing my nose, throat and sinuses. ‘Here’s something that looks like a Dristan commercial,’ he laughs. As I depart, he gives me a souvenir print of my scan. Sadly, I no longer have the image, so I cannot tell whether my parietal lobe is expanded or my lateral sulcus closed up like Einstein’s.
Improvements in magnetic resonance imaging made since the time of my scan now allow scientists to obtain live, moving images of the working brain. Experiments in functional magnetic resonance imaging (fMRI) typically involve scanning a subject’s brain while he or she performs particular tasks. This yields images that highlight the parts of the brain that are temporarily more active. The digital image processing applied to the MRI scans generally displays a section through the whole brain in black-and-white with the active area shown as a coloured highlight. Thanks to this manipulation, we now speak happily of the parts of the brain that ‘light up’ when we think particular thoughts, although, strictly speaking, the observed ‘lighting up’ is an indication of increased blood flow and not necessarily of a particular mental activity.
This new technology is an important aid in diagnosing brain disease, but it also provides a new tool for investigating the way the brain works normally. Many studies are underway to examine aspects of human mental activity that we tend to regard as important in defining who we are as individuals. These include the making of moral choices, the display of prejudice, and the exercise of personal creativity. Even simple decisions without consequences require the exercise of choice, which is an expression of personality. Neuroscientists at the Oxford Centre for Functional MRI of the Brain devised an experiment that required subjects to push buttons in order to switch from an arbitrary state A to states B or C. When subjects chose freely, their action was accompanied by increased activity in one particular part of the brain and reduced activity in another. When the same subject was directed as to what to do by a second person, however, this picture was reversed. The experiment seems to show that the neural mechanisms underlying our assessment of the choices we make are different according to whether those choices are forced or freely made.
But what about a real moral dilemma? Joshua Greene at Harvard University asked his subjects to imagine a situation in which a crying baby threatens to give away the presence of a group of people hiding from enemy soldiers: do you smother the baby to save the lives of the others? His results showed that brain regions associated with planning, reasoning and attention were comparatively more active when people chose to harm some individuals in order to save others. In other words, people think harder when what they decide will have consequences for others. It is what we would at least hope for of our fellow human beings.
Greene’s colleague at Harvard, Jason Mitchell, has been using fMRI to investigate empathy and prejudice. Understanding other people involves imagining ourselves in their position. This is easier to do when the other person is similar to oneself. Mitchell asked his subjects, defined according to their social and political beliefs, to evaluate imagined persons both strongly like and strongly unlike themselves. The brain images he recorded show that the perception of a similar ‘other’ engages a region of
the brain known to be linked to self-referential thought, whereas perception of a dissimilar ‘other’ activates a different region. It does not reveal why, but it does show a little of what happens when, for example, white people more readily associate black faces with negative attributes and white faces like their own with positive ones. Such work may provide a key to understanding racial and other forms of prejudice.
Creative works such as paintings, symphonies and novels are seen as highly personally expressive. But can the creative process be seen as it happens in the brain? Charles Limb at the Johns Hopkins School of Medicine in Washington, DC has tried to catch a glimpse of it by recording fMRI scans of skilled jazz musicians as they improvise at the piano – devising music never thought of or played before. An average made of the brain images of a number of improvisers shows particular areas of the brain activated and others deactivated, suggesting that creativity, too, is localized. Imaging studies of the normal brain such as these gain validity by taking data from a sample population of subjects, not just a single person. I can see how it might be dangerous to interpret one person’s scan in a particular way when looking at something as personal and subjective as prejudice or creativity. Yet I can’t help wondering if these statistical aggregates, like Galton’s composite photographs, risk throwing away the very information they are trying to gather.
Functional MRI is also being applied for less lofty purposes. Brain scans of people on slimming regimes made as they choose whether to eat healthy or junk food, for example, appear to highlight areas of the brain involved in self-control. Product manufacturers and advertising agencies are naturally very interested in this activity of the brain – and in being able to circumvent it. Now that MRI has proven itself as a diagnostic technique and the cost of the equipment is falling, businesses are starting to think about what it could offer them. Gemma Calvert is a former academic psychologist and now managing director of Neurosense, a company that uses brain imaging to probe the mysterious recesses of the consumer’s mind. ‘There is a perception out there that this was developed as a medical technology, and now you’re using it for commercial purposes, and what are you playing at?’ Gemma admits. But major corporations clearly have no such qualms. Neurosense used brain imaging on behalf of a British breakfast programme on commercial television, producing the self-serving result that viewers paid more attention to, and were better able to recall, advertisements screened in the morning.
‘You shouldn’t be sceptical that this technology allows us to see how the brain performs a certain task,’ Gemma chides me. ‘The tricky bit comes when you start asking more social questions. Will you ever really be able to use these technologies to read what I’m thinking? I for one would like to see that.’ The prospect remains theoretical for now, though, requiring scanners with much greater resolution than those available today that could capture the firing of individual neurons in the brain. This might indicate what someone is thinking in response to a certain stimulus. ‘But that still doesn’t get at the sense of experience. The sense-of-being-alive thing is a biggie.’
In San Diego, meanwhile, a company called No Lie MRI shows one direction where this technology is headed. It hopes to use fMRI to enable its clients to assess job applicants and insurance claimants. Because the imaging technique monitors the central nervous system directly, rather than the autonomic nervous system that controls body functions, No Lie MRI claims it is able to bypass American legal restrictions that apply to companies’ use of polygraph lie detectors. Its plan is to set up Orwellian-sounding VeraCentres where subjects will be interviewed while being scanned by an MRI machine. The company is presently lobbying so that fMRI ‘evidence’ will be admissible in American courts. Even neutral organizations such as the British Psychological Society concede that it is probably only a matter of time until brain scans are admitted in court, even though, as with DNA evidence, the aura of science that surrounds them can mean that jurors give them a credence that they do not always merit.
In its zeal to catch fibbers, No Lie MRI may be missing the big picture. To a neuroscientist, and increasingly to all of us, we are our brains. The day may not be far off when a man can walk into court and accuse his own brain of the crime, and the evidence will support his claim. Or, to put it another way, any defendant in future may be able to plead a sophisticated modern equivalent of the insanity plea. The question then is whether it makes any sense to punish the person – or their brain.
The Heart
The heart is a hollow muscular organ of a conical form, placed between the lungs, and enclosed in the cavity of the pericardium.
The heart is pyramidal, or rather turbinated, and somewhat answering to the proportion of a pine kernel.
The heart of creatures is the foundation of life, the Prince of all, the Sun of their microcosm, on which all vegetation does depend, from whence all vigour and strength does flow.
The heart, like a chasuble.
The heart, like a fleshy whoopie cushion.
The heart is deceitful above all things, and desperately wicked.
The heart has its reasons of which reason knows nothing.
The heart is a hungry and restless thing; it will have something to feed upon. If it enjoys nothing from God, it will hunt for something among the creatures, and there it often loses itself as well as its end.
The heart is forever inexperienced.
The heart is a lonely hunter.
The heart, then, is many things to many people, as these varied descriptions attest. The first three descriptions here are by anatomists at different periods, taken respectively from Gray’s Anatomy, Helkiah Crooke’s Microcosmographia and William Harvey’s De Motu Cordis. The next, ‘The heart, like a chasuble’, is from Pantagruel by François Rabelais, who was an anatomist as well as a monk, a lawyer and a writer. On one occasion, in Lyons in 1538, a corpse spoke to Rabelais, at least as told in a contemporary poem by Etienne Dolet. The corpse clearly felt he had got his own back on the judges who had only sought to increase his punishment by sentencing him to death with dissection when he learned he was to be dissected by the great Rabelais: ‘Now Fortune you may rage indeed: all blessings I enjoy.’ The next, possibly more informative, simile comes from Louisa Young’s The Book of the Heart. The remaining statements are drawn from the Old Testament Book of Jeremiah, the seventeenth-century French philosopher Blaise Pascal and his contemporary the English clergyman John Flavel, and the American writers Henry David Thoreau and Carson McCullers.
The idea that the heart represents in some important way our very core goes back to Aristotle and beyond. According to Young, Egyptian and Greek stories of more than 3,000 years ago reveal that the heart was already regarded as the seat of ‘identity, life, fertility, loyalty and love’. Whether this was physiologically true was to remain unknown for many centuries. But the fact that it was absolutely the case in a symbolic sense was underwritten for some 1,300 years when Galen in the second century CE placed the liver, heart and brain in charge of the tripartite body (abdomen, thorax and head), the heart inevitably central of the three.
Unlike all the other internal organs, the heart is clearly discernible as a site of activity: it beats, and beats at a rate that changes in response to the world around it, faster in the presence of a lover, or of danger, slower in sleep and at the approach of death. Classical physicians saw the heart as the source of the body’s heat and as connected with the blood, but it is astonishing that its true function as a pump sending the blood round the body was not understood for so long. Leonardo da Vinci came tantalizingly close to the truth when he observed, as Galen had not, that the heart has four chambers, is highly muscular, and is the source of all blood vessels. Had he only noticed that some of these vessels carry blood out from the heart and others return it, he surely would have drawn the obvious conclusion, and sealed his reputation as rather more than an amateur in the field of anatomy.
When I hold a heart in my hand, it is immediately obvious that it must once have done someth
ing. Compared with the lungs or brain, liver or kidneys, which have an inscrutable uniform texture, this organ has a convoluted architecture. I pull aside the thin folds of fat that wrap it like tissue paper round a piece of china. It has a muscular base with its various chambers (two atria and two ventricles) above. Empty of blood, it is noticeably bottom-heavy. Blood vessels trace wormlike paths across its external surface. This particular heart has been cut away across the aorta, revealing it as a huge tunnel about two centimetres in diameter. I read that the heart pumps 10,000 pints of blood in a day, and that it can squirt blood six feet into the air through this tube. How, in the past, could people imagine that the body simply manufactured blood at the colossal rate that this gaping conduit surely demands? The major vein of the body, the vena cava, is almost as big where it enters the heart. Four other large blood vessels, the pulmonary veins and arteries that transport blood to and from the lungs where it is oxygenated, are about a centimetre across. The whole design reminds me of a diagram of an underground train station. I imagine it will be a puzzle to place the heart back in the prosected body from which I have lifted it so that the severed tubes meet up, but in fact it slips easily back into the hollow left for it by the lungs, finding its correct orientation as it falls into place, like an animal settling in its nest.
In places, I can see wavy flaps of flesh. These are the valves that regulate the blood flow. They create the characteristic double beat of the heart, which is typically spelled out as ‘lub-dub’ or ‘lub-dup’. If you speak these two syllables aloud your tongue will mimic the action of the two sets of valves that regulate the flow of blood. Part of the reason why William Harvey was able to discover the circulation of the blood where Galen and Leonardo had failed may be owing to advances in hydraulic engineering made in the early seventeenth century, including, oddly enough, Pascal’s invention of the hydraulic press. Perhaps these water-pumping contraptions enabled Harvey to see the heart afresh. In any case, Harvey elucidated the mechanism of the heart and blood flow with exemplary scientific clarity, although he remained baffled as to what all the activity was for. This would have to await the discovery of oxygen and the role of red blood cells more than a century later. Sadly, once his book was published, things went less well for Harvey. His friend and biographer John Aubrey wrote that he ‘fell mightily in his Practize, and that ’twas beleeved by the vulgar that he was crack-brained; and all the Physitians were against his Opinion, and envyed him; many wrote against him’.
Anatomies: A Cultural History of the Human Body Page 15
