Hack69.Use Your Right Brainand Your Left, Too

Hack 69. Use Your Right Brainand Your Left, Too

The logical left brain and intuitive right brain metaphor is popular, but the real story of the difference between the two halves of your brain is more complex and more interesting.

There's a grain of truth in all the best myths, and this is true for the left-brain/right-brain myth. Our cortex is divided into left and right hemispheres, and they do seem to process information differently, but exactly how they do this isn't like the story normally told by management gurus and the self-help literature. As with many scientific myths, the real story is less intuitive but more interesting.

Our brains follow the general pattern of the rest of our bodies: two of everything down the sides and one of everything down the middle. With the brain, the two halves are joined directly in the subcortex, but in the cortex the two halves, called hemispheres, have a gap between them. They are connected by a tight bunch of some 250 million nerve fibers, called the corpus callosum, which runs between the two hemispheres (it's not the only way for information to cross the hemispheres, but it's the most important).

Each hemisphere is wired up to sense and act on the opposite side of the body. So information from your right goes to the left side of the visual cortex, and signals from your left motor cortex control your right hand. For higher functions, in which information from both senses is combined, the two hemispheres seem to have different strengths and weaknesses, so that for certain tasks one hemisphere or the other will be dominant.

The origins of the popular myth were studies of patients who had their corpus callosum severed as part of a radical surgical intervention for epilepsy. These "split-brain" patients could function seemingly normally on many tasks, but displayed some quirks when asked to respond to the same material with different hands or when speaking (left brain) rather than pointing with their left hand (right brain).¹

A simple distinction between a left brain specialized for language and cold logic and an oppressed right brain that specializes in intuition grew into the myth we know today. Similar to the 10% myth [Hack #6], this led to the further conclusion that most of us use only half of our brains. Although this distinction may or may not be a useful metaphor in talking about styles of thinking, it is certainly not a useful metaphor for conducting research nor for giving insight into the true differences between the hemispheres.

Any real difference between the hemispheres may be the opposite of what people raised on the left brain bad, right brain good myth would expect. Michael Gazzaniga, who was part of the team that did the original split-brain experiments and is now a very senior cognitive neuroscientist, recently wrote in Scientific American of an "inventive and interpreting" left brain, a hemisphere for structure and meaning, and a "truthful, literal" right brain, limited by a preoccupation with general surface features.² In his research, he found that the right hemisphere contained modules specializing for computationally analyzing perceptions, in a very straightforward way, not looking for any deeper meaning. It's not good at smart search strategies, for example. The left hemisphere is better at high-level associations and problem solving, including language, looking for meaning, and patterns.

6.9.1. In Action

Many of the original demonstrations of hemispheric specialization involve showing an image to just one hemifield of the eyes. Information from both eyes is processed by both hemispheres of the brain, but in both eyes, the information to the left of the focal point is processed by the right hemisphere and vice versa. By making sure someone is looking straight ahead, you can control which hemisphere processes an image by presenting it to the left or the right of his focal pointone hemifield. You have to do it very quickly; as soon as an image appears before them, people will move their eyes to look at it and thus feed the information to both hemispheres. Since this is difficult to do with vision, here's a nonvisual demo you can try at home.³

The left hemisphere is better at processing rapidly occurring sounds and seems better at keeping rhythm; it can hold fancier rhythms and keep them synchronized with a beat better than the right hemisphere.

To show this in action, start tapping a regular beat with your left hand (1-2-3-4- etc.) and then start tapping a fancy beat at the same time with the right hand (jazzy, syncopated, like a melody line to accompany the regular beat). Now, try starting with the regular beat on the right hand (1-2-3-4- etc.), and after a measure or two, start the fancy beat on the left. See what happens. You should find it easier the first way round, with your left hemisphere controlling the more difficult rhythm (your right hand).

Many left-handers actually get the same result as right-handers on this test, so it is not just to do with mere handedness. It probably isn't a coincidence that a piano keyboard is organized with the lower notes, which are used for simpler rhythms, on the left side where they can be delegated to the right hemisphere.

6.9.2. How It Works

By comparing the performance of normal people on tasks that give information to different hemispheres and by comparing responses controlled by different hemispheres, cognitive neuroscientists have uncovered a number of functions that are done differently by the different hemispheres, and some patterns are beginning to appear in the data.

The most obvious specialized function is language. Speech is controlled by the left brain, and understanding the literal meaning of words and sentence grammar is supported by the left brain in most people (but not all). But that doesn't mean that the right brain has no role in language processing. Studies of people with right-brain damage, along with other evidence, have suggested that the right brain may support analyzing global features of language such as mood and implication. If I say, "Can you close the window?" I'm not asking if you are able, I'm asking if you will. A step more complex is to say, "It's cold in here," which is the same request, but more oblique (but maybe not as oblique as "Why are you so selfish?"). It is this kind of pragmatic reasoning in language that some researchers think is supported by the right brain.

The left-brain specialization for language carries over to an advantage in sequential ordering and symbolic, logical reasoning.

The right brain seems specialized for visual and spatial processing, such as mental rotation or remembering maps and faces, dealing with the appearance of things, and with understanding the overall pattern. We have a bias whereby we judge faces by their left side.⁴ You can see a demonstration of this at http://perception.st-and.ac.uk/hemispheric/explanation.html. The web site shows two faces, one looking more female than the other (see Figure 6-8). In fact, the faces are both equally male and female, but the one that looks female has the more female half on the left side (right-hemisphere processing) and the male half on the right side, where it doesn't affect your judgment of gender. Test this now by covering the left sides of the faces in Figure 6-8 and looking again; you can now see that the face you first judged as female is half-male and the face you judged as male is half-female.

Figure 6-8. Both faces are equally male and female, but on different sides; your right brain dominates the perception of gender in faces, so you see one as more male and the other as more female⁵

Like perceiving gender and moods, musical appreciation also appears to mostly involve right-brain-dominant processes (although, as we've seen, for keeping complex rhythms, the left brain is dominant).

Brain imaging studies have suggested that these kind of results can be understood by thinking of the hemispheres as specialized for different kinds of processing, not as specialized for processing different kinds of things. One study⁶ involved showing subjects letters made up of lots of little letters (e.g., the letter A made of up lots of little Ss). The left brain responded to the detail (the small letters) and the right brain to the global picture (the large letter constructed out of small letters). Subsequent work has shown that the story isn't as clear as this study suggests. It seems you can get the left-detail/right-global pattern to reverse with the correct kinds of stimulus-task combinationbut it has confirmed that the hemispheric dominance is due to the demands of the task, not due to the nature of the information being processed.⁷ This gives some tentative legitimacy to the idea that there are left-brain and right-brain styles of processing.

But the important thing is how the two hemispheres combine, not how they perform in artificial situations like those of the split-brain patients. Brain imaging studies of normal people are based on the average results across many brains, and this tends to play down the large variation between different individuals in how the functions are distributed across the brain. Ultimately, however people's brains are wired, they will be using both sides to deal with situations they encounterso it isn't too helpful to become preoccupied with which half does what and whether they are processing with their left or their right.

6.9.3. End Notes

1. It was even claimed the two hemispheres of a patient's split brain were conscious in different ways (http://www.macalester.edu/~psych/whathap/UBNRP/Split_Brain/Split_Brain_Consciousness.html).

2. Gazzaniga, M. S. (1998). The split brain revisited. Scientific American, 279(1), 50-55. (reprinted and updated 2002).

3. This demo is from the book The Lopsided Ape by Michael C. Corballis (Oxford University Press, paperback, 1991), p.267. Many thanks to Michael Parker (http://www.michaelparker.com) for bringing it to our attention.

4. At least we judge holistic features of faces (like gender or mood) by their left side, using our right hemisphere. Neuroimaging research shows left hemisphere involvement in analyzing the parts of faces. Rossion, B. et al. (2000). Hemispheric asymmetries for whole-based and part-based face processing in the human fusiform gyrus. Journal of Cognitive Neuroscience, 12, 793-802.

5. © Michael Burt, Perception Lab, http://perception.st-and.ac.uk.

6. Fink, G. R., Halligan, P. W., Marshall, J. C., et al. (1996). Where in the brain does visual attention select the forest and the trees? Nature 382 (6592), 626-628. There is a great discussion of this article by John McCrone in New Scientist (13 July 1999), reprinted online (http://web.archive.org/web/*/http://www.btinternet.com/~neuronaut/webtwo_features_leftbrain.html).

7. Stephan, K. E., Marshall, J. C., Friston, K. J., Rowe, J. B., Ritzl, A., Zilles, K., et al. (2003). Lateralized cognitive processes and lateralized task control in the human brain. Science, 301(5631), 384-386.

6.9.4. See Also

• Other good starting points for reading about the neuroscience between the right and left brain story are ABC's "All in the Mind" (http://www.abc.net.au/rn/science/mind/stories/s1137394.htm), "Hemispheres" at Neuroscience for Kids (http://faculty.washington.edu/chudler/split.html), and "New Theories of Expression Focus on Brain's Two Sides," article by Sandra Blakeslee (http://members.aol.com/sakrug/dualbrain.html; reprinted from the New York Times).