<p>The first thing we have to establish is whether the left and right halves of our brains do indeed have different functions. The short answer to this is ‘they do’, although things are a lot more interesting and complicated than that. Anyway, just because there are differences between the two hemispheres’ functions, it does not necessarily imply that people can be divided into left- and right-brained thinkers. After all, our stomachs and livers do different things for digestion, but we are not dividing the world into stomach-dominated and liver-dominated digesters. Therefore, the second question we need to ask is whether some people have a left-brain style, and others a right-brain style. Our third question will be, why stop at right- and left-brainers? Maybe people are either top- or bottom-brainers, maybe front- or backbrainers! In fact, the picture of functional division between top and bottom brains is ‘cleaner’ and less ambiguous than between left and right brains, as you will see. </p>.<p>To address the first question on functional differences between the hemispheres, we begin with physical differences. Our left and right hemispheres are similar in weight and volume, but some areas are larger in one or in the other half. The most marked difference is that if you lay the brain bottom-up, and draw an imaginary line down the middle, you will see the RH crosses over the line towards the front of the brain, and the LH crosses over towards the back of the brain. This is a striking and obvious physical asymmetry, and there are others: for example, the left planum temporal is much larger in volume than its right half. But on the whole, there is bilateral (left-right) symmetry in the brain, as in the human body overall. </p>.<p>Most animal bodies have bilateral symmetry, and distinct front and back ends. As creatures move forward through space, there are potential stimuli on their left or their right. They need to be able to turn in either direction, to investigate what the stimulus is, and decide whether to approach or avoid it. Thus, both left and right sides of space (and one’s own body) need to be represented in the brain, for processing the environment and controlling behaviour. Each hemisphere takes this kind of responsibility for one half of the world. For human beings, the right half of the body and space are processed and controlled by the left hemisphere, and the left half by the right hemisphere. So, when you raise your right hand to slap a mosquito on your left arm, it is your right brain that sensed the itch, your left brain that sent the command to the right hand to take care of the offending insect, and your right brain that senses the satisfying sting of the left arm being slapped! Immediately it must be obvious that the left and right brains are in communication with each other, for how else could the right brain have told the left brain to do the needful? The hemispheres are constantly in touch via millions of nerve fibres. So each half of the brain has similar areas for sensation and action—for the other half of the body —and the whole is choreographed perfectly through efficient inter-hemisphere communication. </p>.<blockquote><p>The two halves attend in different ways to the same things. There is a tendency for the left brain to be more attentive to inner states and thoughts, to models and predictions, while the right brain attends more to the external, to things as they are, without imposing ideas from stored knowledge. Absolutely fascinating, but these dichotomies reside within each of us, not between individuals</p></blockquote>.<p>But for ‘higher-order’ functions of the brain, there should be no need for both brain halves to do the same job. For example, the left hemisphere takes care of most of our language comprehension and speech, and the right hemisphere does most of our visual-spatial processing. So you might imagine various functions being assigned to one or the other hemisphere: reading, mathematics, problem-solving, day-dreaming … but it turns out that this is not the way work is divided in the brain. Functions are chopped up into much smaller components. For example, answering ‘What is 3 plus 4?’ is accomplished by your left hemisphere, but answering ‘Which is greater, 3 or 4?’ is accomplished by your right hemisphere. Hearing someone speak is understood at the word and sentence level by your left hemisphere, but the emotional and melodic tone is caught by your right hemisphere. Literal meanings of a word are supplied by the left hemisphere, but figurative meanings are supplied by the right hemisphere. Psychologist Kara Federmeier investigated hemispheric differences in her laboratory, and she has found, for example, that while the left brain comprehends language, it is the right brain that supplies the rich imagery associated with what is being read. And during reading, the left hemisphere is more likely to predict the next word, while the right hemisphere has better memory for exactly what was written. </p>.<p>Deeper perhaps than these are differences in the way the two hemispheres attend to and perceive the world. When I am looking at an object, the details are attended to by my left hemisphere, and the global representation of the whole object is attended to by my right hemisphere. The classic studies showed pictures such as this below to patients with either left or right hemisphere brain damage.</p>.<p>When asked to draw from memory what they had seen, the tendency was that those with intact left brains drew the ‘J’s and those with intact right brains drew the ‘H’. This doesn’t at first glance seem to have much to do with learning and education, although it is exactly the kind of finding that prompts people to say: she’s an analytic left-brainer, or he’s a holistic right-brainer. It’s a bit of a jump from perception to the complexity of learning, but according to psychiatrist and writer Iain McGilchrist, left-right attentional differences could be at the heart of all important dichotomies in the world! The two halves attend <em>in different ways</em> to the same things. There is a tendency for the left brain to be more attentive to inner states and thoughts, to models and predictions, while the right brain attends more to the external, to things as they are, without imposing ideas from stored knowledge. Absolutely fascinating, but these dichotomies reside within each of us, not between individuals. </p>.<p>The fact that our hemispheres have divided many functions of the brain is thus beyond debate, but the way things are divided and then recombined is an area of intense research. Psychologist Marcel Kinsbourne wrote beautifully about this division many years ago: ‘There are no discontinuities in the brain,’ he explained. Although we have ‘divided’ the cortex into lobes, and further subdivided it using terms such as medial, lateral, inferior and so on, in fact every functional system crosses these ‘boundaries’. It’s a bit like food and language traditions in India that stubbornly refuse to fall in line with the state boundaries we draw on the map. Functions cross over the left-right divide, too, and rather than whole activities, it is components of activities that each hemisphere takes on. Thus the massive communication system between the two halves of the brain achieves an integration that is much more complex and subtle than the mosquito example. In a real sense, we could say that the two halves of the brain ‘work together separately’ (like the professor told his students to do in the old joke!). Also, this should make it clear that it is impossible to divide certain general capacities along left-right lines: creativity, intelligence, logical thinking and personality are everywhere in the brain. </p>.<p>Now we can address the second point about left- or rightbrain styles. We are all brain-asymmetric, but for each of us, can one or the other half of the brain dominate, creating a distinct thinking or learning style? The research does not show that some people have stronger left or right brains. Certainly neither half can stand alone: with damage to the left hemisphere, functioning is severely impaired; one does not become free to think and learn in a ‘right-brained’ way. One very technical and thorough study by neuroscientist Jared Nielsen and others examined the scans of over a thousand brains, looking for signs of greater left- or rightbrain strength of connectivity, and found no individual who could be described as ‘left-brained’ or ‘right-brained’ overall. As Federmeier puts it, ‘… it seems safe to say that for the most part we all use both sides of our brains almost all the time.’ </p>.<p><em>(Excerpted with permission from ‘What did you ask at school today: A Handbook of Child learning’ (Book 2), by Kamala V Mukunda, HarperCollins India)</em></p>
<p>The first thing we have to establish is whether the left and right halves of our brains do indeed have different functions. The short answer to this is ‘they do’, although things are a lot more interesting and complicated than that. Anyway, just because there are differences between the two hemispheres’ functions, it does not necessarily imply that people can be divided into left- and right-brained thinkers. After all, our stomachs and livers do different things for digestion, but we are not dividing the world into stomach-dominated and liver-dominated digesters. Therefore, the second question we need to ask is whether some people have a left-brain style, and others a right-brain style. Our third question will be, why stop at right- and left-brainers? Maybe people are either top- or bottom-brainers, maybe front- or backbrainers! In fact, the picture of functional division between top and bottom brains is ‘cleaner’ and less ambiguous than between left and right brains, as you will see. </p>.<p>To address the first question on functional differences between the hemispheres, we begin with physical differences. Our left and right hemispheres are similar in weight and volume, but some areas are larger in one or in the other half. The most marked difference is that if you lay the brain bottom-up, and draw an imaginary line down the middle, you will see the RH crosses over the line towards the front of the brain, and the LH crosses over towards the back of the brain. This is a striking and obvious physical asymmetry, and there are others: for example, the left planum temporal is much larger in volume than its right half. But on the whole, there is bilateral (left-right) symmetry in the brain, as in the human body overall. </p>.<p>Most animal bodies have bilateral symmetry, and distinct front and back ends. As creatures move forward through space, there are potential stimuli on their left or their right. They need to be able to turn in either direction, to investigate what the stimulus is, and decide whether to approach or avoid it. Thus, both left and right sides of space (and one’s own body) need to be represented in the brain, for processing the environment and controlling behaviour. Each hemisphere takes this kind of responsibility for one half of the world. For human beings, the right half of the body and space are processed and controlled by the left hemisphere, and the left half by the right hemisphere. So, when you raise your right hand to slap a mosquito on your left arm, it is your right brain that sensed the itch, your left brain that sent the command to the right hand to take care of the offending insect, and your right brain that senses the satisfying sting of the left arm being slapped! Immediately it must be obvious that the left and right brains are in communication with each other, for how else could the right brain have told the left brain to do the needful? The hemispheres are constantly in touch via millions of nerve fibres. So each half of the brain has similar areas for sensation and action—for the other half of the body —and the whole is choreographed perfectly through efficient inter-hemisphere communication. </p>.<blockquote><p>The two halves attend in different ways to the same things. There is a tendency for the left brain to be more attentive to inner states and thoughts, to models and predictions, while the right brain attends more to the external, to things as they are, without imposing ideas from stored knowledge. Absolutely fascinating, but these dichotomies reside within each of us, not between individuals</p></blockquote>.<p>But for ‘higher-order’ functions of the brain, there should be no need for both brain halves to do the same job. For example, the left hemisphere takes care of most of our language comprehension and speech, and the right hemisphere does most of our visual-spatial processing. So you might imagine various functions being assigned to one or the other hemisphere: reading, mathematics, problem-solving, day-dreaming … but it turns out that this is not the way work is divided in the brain. Functions are chopped up into much smaller components. For example, answering ‘What is 3 plus 4?’ is accomplished by your left hemisphere, but answering ‘Which is greater, 3 or 4?’ is accomplished by your right hemisphere. Hearing someone speak is understood at the word and sentence level by your left hemisphere, but the emotional and melodic tone is caught by your right hemisphere. Literal meanings of a word are supplied by the left hemisphere, but figurative meanings are supplied by the right hemisphere. Psychologist Kara Federmeier investigated hemispheric differences in her laboratory, and she has found, for example, that while the left brain comprehends language, it is the right brain that supplies the rich imagery associated with what is being read. And during reading, the left hemisphere is more likely to predict the next word, while the right hemisphere has better memory for exactly what was written. </p>.<p>Deeper perhaps than these are differences in the way the two hemispheres attend to and perceive the world. When I am looking at an object, the details are attended to by my left hemisphere, and the global representation of the whole object is attended to by my right hemisphere. The classic studies showed pictures such as this below to patients with either left or right hemisphere brain damage.</p>.<p>When asked to draw from memory what they had seen, the tendency was that those with intact left brains drew the ‘J’s and those with intact right brains drew the ‘H’. This doesn’t at first glance seem to have much to do with learning and education, although it is exactly the kind of finding that prompts people to say: she’s an analytic left-brainer, or he’s a holistic right-brainer. It’s a bit of a jump from perception to the complexity of learning, but according to psychiatrist and writer Iain McGilchrist, left-right attentional differences could be at the heart of all important dichotomies in the world! The two halves attend <em>in different ways</em> to the same things. There is a tendency for the left brain to be more attentive to inner states and thoughts, to models and predictions, while the right brain attends more to the external, to things as they are, without imposing ideas from stored knowledge. Absolutely fascinating, but these dichotomies reside within each of us, not between individuals. </p>.<p>The fact that our hemispheres have divided many functions of the brain is thus beyond debate, but the way things are divided and then recombined is an area of intense research. Psychologist Marcel Kinsbourne wrote beautifully about this division many years ago: ‘There are no discontinuities in the brain,’ he explained. Although we have ‘divided’ the cortex into lobes, and further subdivided it using terms such as medial, lateral, inferior and so on, in fact every functional system crosses these ‘boundaries’. It’s a bit like food and language traditions in India that stubbornly refuse to fall in line with the state boundaries we draw on the map. Functions cross over the left-right divide, too, and rather than whole activities, it is components of activities that each hemisphere takes on. Thus the massive communication system between the two halves of the brain achieves an integration that is much more complex and subtle than the mosquito example. In a real sense, we could say that the two halves of the brain ‘work together separately’ (like the professor told his students to do in the old joke!). Also, this should make it clear that it is impossible to divide certain general capacities along left-right lines: creativity, intelligence, logical thinking and personality are everywhere in the brain. </p>.<p>Now we can address the second point about left- or rightbrain styles. We are all brain-asymmetric, but for each of us, can one or the other half of the brain dominate, creating a distinct thinking or learning style? The research does not show that some people have stronger left or right brains. Certainly neither half can stand alone: with damage to the left hemisphere, functioning is severely impaired; one does not become free to think and learn in a ‘right-brained’ way. One very technical and thorough study by neuroscientist Jared Nielsen and others examined the scans of over a thousand brains, looking for signs of greater left- or rightbrain strength of connectivity, and found no individual who could be described as ‘left-brained’ or ‘right-brained’ overall. As Federmeier puts it, ‘… it seems safe to say that for the most part we all use both sides of our brains almost all the time.’ </p>.<p><em>(Excerpted with permission from ‘What did you ask at school today: A Handbook of Child learning’ (Book 2), by Kamala V Mukunda, HarperCollins India)</em></p>
