It's time to rethink whatever you thought you knew about how the right and left hemispheres of the brain work together. iStockphoto hide caption toggle captioniStockphotoIt's time to rethink whatever you thought you knew about how the right and left hemispheres of the brain work together. iStockphotoSometimes ideas that originate in science seep out into the broader culture and take on a life of their own. It's still common to hear people referred to as "anal," a Freudian idea that no longer has much currency in contemporary psychology. Ideas like black holes and quantum leaps play a metaphorical role that's only loosely tethered to their original scientific meanings. What about the idea that some people are more right-brained and others more left-brained? Or that there's a distinctive analytic and verbal style of thinking associated with the left hemisphere of the brain, and a more holistic, creative style associated with the right? Are these scientific facts or cultural fictions? An infographic reproduced just last month at Lifehack.org, for example, promises to explain "why you act the way you do" by revealing "which side of your brain you tend to use more." An article at Oprah.com explains "how to tap into right-brain thinking." And decades of research using behavioral and neuro-scientific techniques do reveal fascinating and systematic differences across brain regions. On the other hand, some recent headlines challenge the left brain / right brain dichotomy. One highly publicized paper, summarized at The Guardian, failed to find evidence that individuals tend to have stronger left- or right-sided brain networks. A new book by Stephen M. Kosslyn and G. Wayne Miller argues that the left / right brain divide is largely bogus, and should instead be replaced by a top brain / bottom brain distinction. So while there's something deeply compelling about the clear-cut, right-brain versus left-brain classification (or is that just my left hemisphere speaking?), we have good reasons for skepticism. The real story, as you might expect, is a bit more complicated — but arguably more interesting — than the infographics and popular headlines seem to suggest. To get a clearer picture of what we do and don't know about hemispheric brain differences in humans, I was fortunate to have an opportunity to interview a leading cognitive neuroscientist, Kara D. Federmeier, whose research focuses on language, memory and hemispheric asymmetries throughout the lifespan. Dr. Federmeier is a professor of psychology at the University of Illinois at Urbana-Champaign, where she's also affiliated with the Neurosciences Program and The Beckman Institute for Advanced Science and Technology. (And, full disclosure, she was also one of my first scientific mentors and co-authors.) One idea that's often heard in popular discussions of psychology is that the left brain is the seat of language and more "logical," while the right brain is more creative. Is there any truth to this idea?
Early studies of hemispheric asymmetries often relied on "split-brain" patients who had the corpus callosum — the bundle of neural fibers that connects the two hemispheres — severed as a treatment for severe epilepsy. In such studies, information could be provided to a single hemisphere at a time by presenting people with input to one side of the visual field, since the right visual field is processed by the left hemisphere, and vice versa. Your lab uses contemporary neuro-scientific techniques, such as measures of brain wave activity (EEG and ERP) to investigate hemispheric asymmetries, and typically does so in individuals with intact brains. How do you do so, and do your findings corroborate or challenge earlier inferences made from the behavior of split-brain patients?
It makes sense to have specialized brain regions, just as it makes sense to have divisions of labor in other areas of life. But why have specialized hemispheres? In other words, do you think there's something general that can be said about the sorts of processing that occur in the left hemisphere versus the right hemisphere, or is each simply a constellation of somewhat distinct, specialized regions?
What's surprised you most about the hemispheric asymmetries you've found (or failed to find!) in your own research?
Another popular idea is that some people are more "left brained" and others more "right brained." Is there any evidence for individual differences in the extent to which people rely on one hemisphere versus another? More generally, what kinds of individual differences do you see in hemispheric specialization?
Finally, can you recommend any accessible resources for readers who want to learn more about hemispheric asymmetries?
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