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.

[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.

About the author


Dr Jeremy Dean is a psychologist and the author of PsyBlog. His latest book is "Making Habits, Breaking Habits: How to Make Changes That Stick". You can follow PsyBlog by email, by RSS feed, on Twitter and Google+.

Published: 18 March 2008

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