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Moving Beyond Left Brain, Right Brain, Neuroskeptic goes in-depth with Michael Corballis

By Neuroskeptic

“Are you a left brain or a right brain person?” The idea that the logical left half of our brain stands in opposition to the creative right is immensely influential – but neuroscience paints a much more complex picture of what left and right mean in the brain.

In this interview I asked Michael Corballis, Professor at the University in Auckland, New Zealand, to explain why the myth of the binary brain has been so popular. In January, Corballis published a paper called Left Brain, Right Brain: Facts and Fantasies in PLOS Biology and it’s been read over 25,000 times since then.

This is the second in my series of interviews for PLOS Neuro as Contributing Editor! If you missed it, the first post, with Dr Srivas Chennu, is here. My regular blog, at Discover Magazine, is Neuroskeptic.

corballisNS: “What made you decide to write about the left brain vs. right brain issue?”

MC: I was actually invited to write the article, but readily agreed as I have long been interested in handedness and brain asymmetry, and the myths surrounding them.

“Why has the left brain/right brain idea proved so popular, despite years of skepticism from neuroscientists (such as yourself)?”

I think dichotomies have a natural attraction, and brain asymmetry provides pegs to hang them on. We love to distinguish male from female, good from evil, day from night, introvert from extravert, Western from Eastern, science from art, and so forth. Appealing to brain asymmetry also provides a sense of mystery, since the two sides of the brain look pretty much alike, yet seem to operate differently—although the differences are exaggerated to help preserve the myth of duality. That mystery also seems to reinforce the idea that the mind is more than just a material brain, an idea often attributed to Descartes but also well entrenched in religious doctrine.

Dichotomies are really the result of lazy thinking—after all, even black and white are ends of a continuum! In the 1970s, someone coined the term “dichotomania” to refer to our habit of reducing things to dichotomies. Convenient, but usually wrong and sometimes dangerous.

“In the paper you discuss how historically, left handedness was commonly seen as abnormal, strange and indeed ‘sinister’. But today, it seems to me that left handedness is actually viewed positively e.g. it’s widely believed to be associated with artists and creativity. Why do you think this is?”

In popular discourse, at least, left-handedness is linked to dominance of the right brain, and ideas about brain duality that emerged during the 1960s and 1970s attributed positive qualities to the right brain. This was partly fed by protest movements of the time—against the Vietnam War, the military-industrial establishment, and male domination. The split-brain research carried out by Roger Sperry (who won the Nobel Prize for his work) seemed to provide neurological support, since it showed that the right brain was not merely the “nondominant” or “minor” hemisphere (as previously assumed), but was in some respects superior in function to the left hemisphere.

The distinctions between left and right brains were nevertheless exaggerated, even by Sperry. The positive attributes of the right brain were then carried over into the notion that left handers are more artistic, creative, and intuitive.

We now know that handedness is only weakly correlated with brain asymmetry, and that most left handers are left-brained for language, just as right handers are. Even so, the association of handedness with brain asymmetry has been difficult to dislodge, and the notion that left-handedness imposes special benefits is probably fed by a general move to promote the cause of minorities or people who are disadvantaged. This of course can be a good thing, even if it’s not well founded, since left-handers have been pilloried throughout history simply for being different. There’s little evidence that left-handers as a group are better endowed artistically or creatively, but neither is there good evidence that they are deficient in intellect or skill. They sometimes have the benefit of surprise (e.g., in some sports), and the sense that they might be regarded as deficient may have spurred many of them to high achievement!

“You explain that lateralization goes a long way back in evolution, and that most animals are right ‘handed’ (or pawed). But do we know why it’s the right side that’s always usually dominant? Couldn’t it just as well have been the left?”

Human brain showing Broca's and Wernicke's areas (upper diagram) and areas of chimpanzee brain showing leftward enlargement (lower diagram). Image credit: Todd Preuss, Yerkes Primate Research Center
Human brain showing Broca’s and Wernicke’s areas and areas of chimpanzee brain showing leftward enlargement. Image credit: Todd Preuss, Yerkes Primate Research Center

It may not be true that most animals are right handed (or pawed) but many are. Just why it’s the right is not really known, although it may be ultimately linked to other asymmetries, such as the leftward asymmetry of the heart. It may have to do with the fundamental molecular asymmetries of biological tissue (e.g., the DNA molecule) but we don’t really know.

Compared with the asymmetries of the internal organs, though, handedness and brain asymmetries are weak and fairly easily reversed, as in those individuals who are left-handed or right-brained for language. Left/right reversal of the heart, in contrast, is very rare. I think there is a trade-off between bilateral symmetry and unilateral specialization. Even our hands are fundamentally the same, despite the superior skill for some things in the dominant hand. We often need to use both hands rather than rely on just one.

“You say that left and right brain is a convenient peg upon which to hang a simplistic dichotomous view of the mind. I wonder whether today’s neuroscientists aren’t still prone to this? For example, while most neuroscientists tend to be dismissive of left/right brain dualism, the influential ‘cognitive frontal vs. emotional limbic brain’ idea has always struck me as being rather like left/right, albeit rotated by 90 degrees.”

Both dualities are overly simplistic, but there is a better case for distinguishing frontal (or cortical) from limbic, even on anatomical grounds. The left and right brains are much more alike structurally and functionally than are the cerebral cortex and the limbic system.

One thing that partially drives the left-right myth is the seeming mystery that left and right brains are so alike anatomically yet function differently, at least in some respects, and it heightens the mystery to exaggerate the differences. We like dichotomies, and we like mysteries!

The left/right obsession goes well back beyond the brain to myths about the left and right hands, and to philosophical questions about what distinguishes left/right mirror images.  In virtually all cultures the right is associated with positive values and the left with negative ones, probably because of the superior skill (dexterity) of the right hand in most people. With duality dumped on the brain, the balance was restored, with the right brain seen as complementary rather than inferior to the left. Perhaps as a result of protest movements, the right was, and still is, often seen as superior. Iain McGilchrist’s 2009 book The Master and his Emissary is a classic and popular modern example.

I’m not quite sure why you suggest frontal vs limbic rather than the cortex vs the limbic system. It’s true that the frontal lobes are sometimes depicted as especially critical to human evolution and the emergence of language, logic, and the like. But it is not entirely clear that the frontal lobes are that much different from those in other primates when scaled for total brain size, and the emphasis is now on cortical circuits that connect different brain regions, especially frontal, temporal and parietal lobes. Even so, you’re right—we still tend to treat these cortical systems as though disconnected from limbic systems devoted to emotion.

“We’ve discussed left/right myths that deserve to be forgotten, but do you think there are any genuine lateralization phenomena that aren’t as widely known as they should be?”

Of course there are differences between the left and right brains, and a more nuanced understanding would help. It is true that the left brain is dominant for language in the great majority of people, and more so with respect to production than comprehension. And there are functions, such as spatial attention and processing of emotion, where the advantage lies with the right hemisphere—although the advantage is not absolute.

One thing that should be more widely known is that brain asymmetry is not simply reversed in left-handers. Some 70 to 80% of left-handers are left-brained for language, just as are some 95% of right handers. This of course runs counter to T-shirts proclaiming that left handers are in their right minds—and popular articles often proclaim that left handers are right brained.

“You recently published a popular book called The Wandering Mind, an overview of resting-state brain activity, mind wandering and the ‘default mode network’. There are many interesting facts about this topic, but are you aware of any popular ‘mind wandering’ fantasies of the same kind as the left brain/right brain mythology?”

1404705525338Mind wandering mostly has a rather bad press. This is partly driven by a desire for control on the part of teachers and parents, who want their kids to pay attention. Mind wandering also runs counter to the current fashion for mindfulness, which advocates the benefits of focusing on the present and on one’s own body. Mind wandering is in many respects the opposite, allowing us to wander mentally in space and time, and even to inhabit the minds of other, whether real or imaginary. My guess is that both are beneficial—mind wander is a bit like taking a holiday, while mindfulness is like returning home, and we need a balance between the two.

Although mind wandering may have a bad press and induce feelings of guilt, it exists in other guises that are pleasurable and even admired. We like watching soap operas, going to movies, or reading novels, which are forms of induced mind wandering, and known to have benefits in the way we learn to understand people and develop empathy.  And although teachers often resent dreamy kids, they sometimes understand that the ones whose minds wander are often the more creative and interesting ones.

Any mythology surrounding mind wandering, though, is not really the same as that surrounding left and right, since mind wandering is a fairly well established phenomenon. Much of the left/right mythology is founded on misunderstanding or oversimplification of brain function.

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond.neuroskeptic

On Twitter @Neuro_Skeptic


The views expressed in this post belong to the author and are not necessarily those of PLOS.

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