Two Brains for the Price of One?
Mind-myth 7: Everyone has heard the idea that our left-brains are logical, verbal, rational and scientific while our right brains are spatial, emotional, intuitive and creative. Like some of the mind-myths covered in this series, there's a solid grain of truth here but its extent has been wildly exaggerated.
Left side language
The biggest grain of truth is that our verbal powers are concentrated in the left side of our brains. It was Nobel Prize winner Roger W. Sperry who, in the 1960s, first showed that the left hemisphere is specialised for language (Corballis, 2007). He was studying patients suffering from crippling epileptic fits who had decided to undergo surgery to try and relieve their symptoms.
The surgery cut the bundle of white matter - the corpus callosum - that connects the two hemispheres of the brain. Along with successfully treating their epilepsy, these 'split-brain' patients exhibited some strange new symptoms.
Sperry found that after the surgery patients were unable to name objects with the, now disconnected, right side of their brains. Their left-brains, however, seemed to have retained this ability. This lead him to propose that the left hemisphere is specialised for language.
But this specialisation didn't mean the right hemisphere had no language powers at all. Further experiments suggested the right hemisphere could indeed still process language, just to a lesser degree. For example, patients were able to point to the written names of objects which were presented to their right-brain, although they found themselves unable to say the word.
Right side?
Not long after the left-brain language discovery, researchers began to wonder about the right hemisphere's special skills. Sure enough the right hemisphere seemed to perform better in some tasks:
- Mentally rotating shapes.
- Identification of melodies.
- Detecting facial emotions.
This seems to correspond well with the myth, after all right-brains are spatial, emotional and creative, aren't they? Well, yes, but the actual differences found in these experiments are relatively small, especially when compared to the specialisation of the left hemisphere in language.
To completely lose a particular mental faculty, a person normally needs to suffer damage to a particular area in both the left and right hemispheres.In a classic paper published in the journal Neurology, renowned neuropsychologist Brenda Milner points out that while there are many measurable functional differences between the left and the right-brain, there are actually many more similarities between the two hemispheres (Milner, 1971). Perhaps the clearest evidence of this is from studies of brain damage. To completely lose a particular mental faculty, a person normally needs to suffer damage to a particular area in both the left and right hemispheres.
Research continues apace into the functional differences between our right and left hemispheres. But while findings about lateralisation continue to point out surprising new differences about our hemispheric twins, the overall message remains the same: apart from language these differences are generally small. Even in language, to perform at our best, we need both sides of our brain working together.
» Find out if any other mind-myths catch you out.
[Image credit: Gaetan Lee]
References
Corballis, M. C. (2007) The dual-brain myth. In: S. D. Sala (Ed.). Tall tales about the mind and brain: separating fact from fiction. Oxford: Oxford University Press.
Milner, B. (1971). Interhemispheric differences in the localization of psychological processes in man, Neurology, 8, 299-321.
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Here is the link to Dr Jill Bolte Taylor's TED lecture My stroke of insight.
http://www.ted.com/index.php/talks/view/id/229
She is a brain scientist who describes her own stroke.
Jo
Just one note/question on needing damage on both sides of the brain to eliminate a function.
For speech and language processing, aren't Wernicke's and Broca's areas left side only? If I am remembering that correctly it would make language one of the very few things that is not lateralized.
In her talk Dr Taylor actually reinforces the idea of two functionally different hemispheres, describing the functionality with parallel processing in the one vs serial processing in the other half of the brain. Maybe the author of the article can comment on what seems to me her adherence to the myth.
Yes, I would love it if you could comment on Dr Taylor's suggestion that the two hemispheres have specialised functions.
And who came up with the myth that your dominant eye tells you which is the dominant side of your brain?
I'm an artist who loves science so I find the whole right brain-left brain thing funny is how much credence it's given among artists.
My right eye is dominant so by their logic my left brain is dominant. Funny on so many levels, especially when they continue to insist that even after I explain why it's a myth and that even were it true the fact that I'm legally blind in my left eye would force my right to be dominant anyway.
Noadi: The thing with sight is that it doesn't work like arms/legs. Your right eye isn't just connected to the left side of your brain; it's connected to both sides. What actually happens is that each half of your visual field connects to the opposite hemisphere. So basically the image formed by light hitting each retina is split between the two hemispheres.
Which means that right/left eye dominance is almost certainly not due to left/right brain dominance, though not just because the right/left brain dichotomy isn't as clear cut as some believe.