by Rik Smits
This produced a new insight that would persist into the twenty-first century. The brains of left-handers were not the mirror image of those of right-handers; instead they were rather less markedly lateralized. More than two out of three left-handed people have their language centres in the left half of their brains, just like right-handed people. The remainder fall into two groups, one with ‘everything’ on the right side and another whose linguistic capacities are divided between left and right. People in this latter group have a slightly better chance of avoiding aphasia after suffering a serious head wound, although the advantage is only slight. One might hope for their sakes that they never have the opportunity to discover by such a route just how unusual their brains are.
People would not be people if the discovery of functions in which the right brain seemed to specialize had not immediately become the basis for new myths and misconceptions. The apparent contrast between right-brain tasks and the specialist functions of the left brain – counting, arithmetic and the production and processing of language – were quickly transformed by all kinds of experts and semi-experts (in ways that percolated through even to women’s magazines) into a concrete antithesis between a cool, calculating, analytical ‘person’ who resides in the left half of our heads and a warm, emotional, holistic character ensconced in the right half. From there it was only a short step to the idea that a person’s character was ultimately determined by whether the right or left half of the brain held the reins. Artistic, musical and highly emotional people were thought to be right-dominant, whereas the more analytically inclined cold fish clearly had brains in which the left side was boss.
This fitted perfectly with the archetypal social distinction between arts and sciences, so perfectly in fact that practically everyone failed to notice the strange consequences of such a train of thought. The boffin or nerd is a clever but quiet, shy, socially awkward figure, whereas the creative, hard to pin down, humanities-oriented libertine thrives on social intercourse. The latter holds forth, polemicizes and writes romantic letters, dramatic poems or passionate literature. Supposedly left-oriented scientists seem far less able to handle that archetypal left-brain function, language, while right-dominant types rely upon it. For decades no one pointed out the contradiction here, or suggested it might pull the rug out from under the theory of dominance. Instead the differences between the two halves of the brain were simplified into a table of opposites, an ostensible order that was permitted to be inconsistent and hardly ever tested against reality. It seems we just can’t help ourselves.
No less inevitable was the link made between the dominance model and hand preference. Left-handers were stamped as generally less verbal but more creative than right-handers and above all more geared towards the visual. For many left-handed people, traditionally put down as clumsy, this may have been a comforting thought, but that’s all it amounted to in the end. No evidence has ever been found for their greater artistic endowments. Meanwhile the development of new techniques, which offer far better opportunities for glimpsing the workings of the brain, has made it seem a good deal less likely that such evidence will ever be found. Those techniques did not arrive until the final decades of the twentieth century.
Promotional material for a course that promises a more harmonious life. Telling left from right has proven too difficult for the organizers of the course.
As Jean-Luc, still a little confused after his madcap ride in the nose cone of the rocket, crawled into the space station he looked up, straight into the moonface of the commander.
‘Mr Picard, welcome on board the International Space Station. How was Baikonr? Is everything still such a mess there in Kazachstan? They’ll never learn, you know; those Russkies need a tsar to order them around. Glad you could come. We always have a good laugh with the French.’
‘Thank you, er, I’m happy to hear that,’ Picard answered, somewhat taken aback. ‘I hope I can make myself useful here.’ And he paddled along behind the man who would be his boss for the next two weeks as they made their way to the residential area of the space station.
‘Absolutely. Don’t you worry. But first I’d like to show you something.’ The commander pointed towards a small porthole in the side wall of the module. With a sweep of his arm he nudged the weightless, unsuspecting Picard in the right direction.
‘Ow! Merde – sorry, I still have to learn to slow down in time.’ Crossly, Picard rubbed his cheek, which had just made rather abrupt contact with the porthole. But then he forgot the pain, mesmerized by the view. Outside, surrounded by millions of sparkling, pin-prick stars, was a huge dark ball with a bright golden aura: the earth, with the sun concealed behind it. It was night down there.
The commander tapped the window and pointed: ‘Look. See that patch of light? No, further to the right: Paris! I thought you’d like that.’
Picard looked. A patch of light was all he could see. But in his mind’s eye an image unfurled of cars, buses and people in a great swarming mass. He could imagine the noise, the sight of the brightly lit shops and the theatre doors just opening, or perhaps already closing, the dizzying complexity of all the things that go to make up a city. What was left of all that from here, less than four hundred kilometres above the earth’s surface? A fuzzy splodge.
The view that a novice space traveller would have of Paris from an earth orbit bears rough comparison with our image of a healthy brain functioning normally. Inspired mainly by rapidly advancing digital technology, one new instrument after another appeared on the scene in the late twentieth century, enabling us to catch a glimpse of what goes on inside the skulls of people with normal brain function, without any need for surgical breaking and entering, even without anaesthetics. The most important new technique dates from the early 1990s and is known as fMRI, or functional Magnetic Resonance Imaging. It was initially called Nuclear Magnetic Resonance Imaging, but that name fell into disuse in the medical field because it created undesirable associations with radioactivity.
Where brains are hard at work they use a great deal of energy in the form of oxygen, supplied to them in the haemoglobin that fills red blood corpuscles. In the more active areas of the brain, blood flow quickly becomes more intense than in areas where little is happening, and the hungry neurons extract so much oxygen from the corpuscles streaming towards them that their haemoglobin becomes oxygen-poor, giving it different magnetic characteristics from oxygen-rich haemoglobin. This difference can be measured, creating a profile of brain activity.
The measurement process is at first sight rather like making an x-ray photograph, but without the use of dangerous rays. When oxygen-rich haemoglobin comes into contact with a magnetic field, it forms a very weak opposing magnetic field. One might say it works a tiny bit against the external magnetic field, whereas oxygen-poor haemoglobin forms a barely detectable magnetic field of its own in the same direction, thereby slightly increasing the strength of the external field. So if a body is exposed to a uniform magnetic field on one side, we can measure, on the other side, point by point, how much of the strength of that field remains. The ‘shadows’ shown up by this process indicate that somewhere between the source of the field and the point of measurement lies tissue the magnetic forces are finding harder to penetrate. The deeper the shadow the more resistant the brain matter.
The contraption in which all this takes place is the MRI scanner, a huge, powerful, ring-shaped magnet into which it’s possible to slide an entire human body. Once the subject is inside the machine, a base measurement is made, or a map of the brain at rest. This is achieved by producing at great speed, with the help of sophisticated computing techniques, a large number of adjacent magnetism profiles, in other words magnetic photographs of cross-sections of the head. A sequence of slices, so to speak, is made from left to right and another from front to back. The two sets of images are then combined to create a three-dimensional picture of the brain.
If that brain is now given something to do – such as recognizing a word or an image,
counting to ten or solving arithmetic – the areas of the brain involved in that task are activated immediately. The scanner again records a complete three-dimensional series of slices, this time of a thinking brain. The differences between that set of images and the base measurements indicate the places in the brain that have been activated. Their intensity shows the degree of activity.
So we first measure the structure of a person’s brain, then the activity taking place in it. We know exactly what tasks the brain is performing, since they have been given to the brain by the people making the measurements. This is what the ‘f’ in fMRI stands for: the measurement and localization of an activity or function.
There have been huge advances in fMRI since the final years of the twentieth century. Every month, newspapers and magazines feature new images of the brain with active areas lit up in fetching colours, usually with captions saying that we now know where human brains recognize words, experience joy, generate a sense of embarrassment or whatever else it might be. This is a great deal more than we used to be able to see, and it is indeed truly impressive, but at the same time, all we can expect from this technique is a rough, coarse-grained map. As yet we have taken only a small step on the long road towards unravelling how the brain works. Even with the best scanning techniques in the world we see only the kind of thing our space traveller saw on the surface of the earth: indistinct splodges. They tell us which areas are involved in certain tasks, but not exactly what they do or why. We see Paris, but not the streets swarming with people, cars and buses that make Paris what it is. We cannot see the cafes, shops and theatres, let alone understand where all those people and cars are going, or what happens in those cafes and shops.
Initially fMRI results brought nothing new to light that could be of relevance to hand preference, which is hardly surprisingly, since people were by then a little tired of studying left- and right-handedness and there was a lack of exciting new ideas. Left-handers weren’t even regarded as valuable test subjects. Their brains were known to differ a fair bit from the right-handed standard, not just when it came to manual dexterity but in the positioning of the much investigated linguistic functions. Their non-standard patterns of brain activity would only make it unnecessarily difficult to come up with an unambiguous interpretation of data from groups of test subjects.
This changed in 2009, and again it was the Max Planck Institute in Nijmegen, along with the Donders Institute for Brain, Cognition and Behaviour in that same Dutch city, that produced new research on the subject. Studies showed that various visual functions are linked to hand preference. In recognizing faces, left-handers use more neurons in the left brain than in the right. This shattered one cornerstone of what we thought we knew about the geography of the brain, since facial recognition had for decades been a textbook example of a capacity located exclusively in the right half of the brain.
It had already been known for some time that the brains of left-handers are rather less lateralized than that of the average right-hander. This explains why left-handed people have a slightly lower risk of becoming aphasic if the left half of the brain is damaged. What the researchers in Nijmegen discovered was that the brains of left-handers differ from the right-handed norm in many other ways as well. In recognizing faces, bodies and chairs, right-handed people deploy mainly the right cerebral hemisphere, whereas left-handed people make more use of the left. In most cases it’s correct to talk of facial recognition as a right-lateralized function, but this cannot be said of left-handers. Both at certain locations and more generally, the two halves of their brains differ rather less.
This raises all kinds of interesting questions. For example, are the memories of left-handed people organized differently and what does this tell us about the way memory works? One theory of memory is that the remembered meaning of a word – a concept – is not simply an abstract thing that exists independently of all else; rather it becomes rooted in the physical characteristics and sensations of the bearer of the concept, if at all possible. This is known as embodied cognition. In concrete terms it implies that the meaning of a verb of action such as ‘lick’ or ‘kick’ consists in essence of the activation of the area of the brain that comes into play when we are in reality about to lick or kick something, shortly before the motor cortex sends the appropriate command to the muscles. In other words, the comprehension and understanding of the concept ‘to kick’ consists of carrying out, up to a certain point, the planning phase of the act so named.
The areas of the brain that light up in left-handers and right-handers when verbs for actions involving hand movements are recognized. The meanings of such words seem to be stored not only in the areas of the brain that are concerned with motor functions but in the side of the brain that controls the preferred hand.
If the theory of embodied cognition holds water, then it would be logical to expect left- and right-handed people to differ in their ways of understanding and remembering those verbs that refer to actions carried out by the hand, such as ‘pinch’, ‘throw’, ‘pick up’ or ‘draw’, aided as they are by the pre-motor areas for their preferred hand. This turns out to be the case. Results of fMRI tests show that with right-handers the relevant areas in the left cerebral hemisphere are highlighted and with left-handers the corresponding areas in the right.
Add to this the remarkable phenomenon discovered in 2009 by Daniel Casasanto – that people respond more positively to things in the real world that appear on the same side as their preferred hand than they do to things on the other side – and little remains of the image we once had of the differences in how the brains of left- and right-handed people are laid out. Those differences can sometimes be far greater than we used to think and they seem to relate to a far broader range of functions, perhaps even to all functions. Strong lateralization, with tasks that are entirely reserved for one half of the brain, seems to be far less in evidence than we once imagined. Lateralization was once seen as a monument not only to our knowledge about our brains but to the difference between us and other species. That monument is now being shaken to its foundations.
Despite the apparently larger, more varied and more polymorphic differences that have been discovered between the brains of left-handers and those of right-handers, left-handed people remain as ordinary and inconspicuous as ever. The most important conclusion may therefore be that our brains are far more flexible than we once thought.
All this is not to say that the beliefs of the second half of the twentieth century were entirely incorrect. On the contrary. There’s no reason to doubt that in the majority of cases the right cerebral hemisphere is concerned with such things as spatial orientation, the creation and recognition of melodies and the interpretation of images. The left is usually better at counting, arithmetic, keeping track of time and processing language.
Yet we need to take into account that many of the functions we recognize as such are not single entities at all but the result of a meshing together of a wide range of smaller tasks and capacities. To think, to understand, to read and write – these are brief, simple terms for unfathomably complex processes. It would be quite strange if all the processes involved in such higher functions were located in either one cerebral hemisphere or the other.
The functions we can positively identify as located in a specific place in one or other half of the brain will tend to be relatively straightforward, abstract processes, dozens of which go to make up what we think of as higher functions. Perhaps the location of a given function is not even particularly important. The overall difference in approach between the two halves of the brain may be far more relevant. It may be that the difference between our cerebral hemispheres has less to do with the specific processes that reside in them than with how those processes happen. In other words, they may differ more in their way of working than in what they do.
To find one possible indication of this we need to turn our attention back to our hands. We can all make a fist, lay one hand flat on a table or drum a tabletop with
our fingers. People with brain damage can do all these things too, so long as they aren’t hampered by severe paralysis. All of us, including brain-damaged people, can easily mimic those three acts in a given order after they have been demonstrated to us once: ball fist, lay hand flat, drum fingertips. Unless, that is, there is damage to the left side of the brain. The performance of each act still presents no difficulties, but getting them in the right order does. The revelatory thing here is that whether the patient happens to be left- or right-handed, this difficulty is manifested not only by his or her right hand, which is controlled by the damaged left brain, but to an equal degree by the left hand, controlled by the undamaged right brain.
Clearly the problem does not lie in hand-control. It seems those damaged parts of the left brain are involved not so much in the performance of the acts themselves as in making them happen in the required order, with either hand. Healthy people and people with damage to the right brain generally have no problem at all with simple sequencing tasks.
This suggests that the planning and organization of complicated undertakings, in other words the compiling of a programme of activities that must be carried out in a specific order, is a speciality of the left brain. It’s precisely this capability that lies at the root of William Calvin’s ideas about the causes of hand preference. Ever since Liepmann’s discovery in the early 1900s that the left cerebral hemisphere is involved in complex motion in both halves of the body, this breakthrough has been only a short step away. It also tallies with the likelihood that brain damage on the left side will cause linguistic problems, since the processing of language is all about putting together and plucking apart sentences and words, structures that have to be compiled in precisely the right order. In fact language processing involves a highly complex arrangement of levels and subsidiary tasks, each of which has its own strict rules about order and sequence that fall under the heading of grammar. Each phrase, whether spoken or heard and understood, requires the processing of a vast pile of sequence-sensitive data with such astonishing rapidity that it doesn’t delay us at all.