The Puzzle of Left-Handedness (22 page)

Although Broca’s Law, as it was known, was generally accepted, it had never been tested. Left-handers are relatively unusual in any case, and people with aphasia and not too much other brain damage are rare. It’s therefore very unusual for a neurologist to come across a person who is both left-handed and aphasic but otherwise healthy. It would take a world war to bring enough of them together for reliable research. Conrad found himself in the middle of that war, and he discovered that a considerable percentage of the left-handed sufferers from aphasia he was treating had been shot in the left side of the head, just like the right-handed aphasics brought to his hospital. Clearly the widespread assumption about reversed brains in left-handers was false.

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 f
MRI
, 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 f
MRI
stands for: the measurement and localization of an activity or function.

There have been huge advances in f
MRI
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 f
MRI
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.