Mind myth 2: Left brain right brain

Practically all brain based pseudosciences encompass some version of the left brain right brain / whole brain myth. The myth is actually nothing new and dates back at least to Broca and Wernicke's findings in the 1860's about the role of the left hemisphere in language. This lead to a dichotomania, much as we have now, for the rest of the nineteenth century. It culminated in the Victorian educational ideal of ambidexterity, in order to promote two-brainedness. Lord Baden-Powell, the founder of the Boy Scout movement, was one of the supporters of the ambidexterity movement - in order to get more effective soldiers! This history was almost forgotten, but fortunately brought to light again in 1985in separate publications by Anne Harrington and Lauren Harris (see references at the end of this post). Also see my previous blog posting Whole-brain Half-wittedness.

Almost 60 years passed before the myth was resurrected again following on Roger Sperry's split brain research in the 1960’s. Sperry and colleagues bisected the corpus callosum and other cerebral commissures of patients in order to control intractable epilepsy. They then found the separated hemispheres of their patients to have different specialised abilities, the left’s mainly related to language comprehension and production, the right’s mainly related to spatial perception.

The myth-makers jumped into action and soon long lists of supposed left brain and right brain functions were generated. The left brain was associated with Western logic and the right brain with Eastern mysticism. Western education was supposed to neglect the right hemisphere and whole-brain learning became the goal. Children were classified as left brained or right brained on the basis of simple tests of undetermined validity and reliability. Predictably this lead to views that the right hemisphere was inactive and had to be activated by various simplistic means.


Neuroscience moved on and most of the above were soon proved wrong. It became clear that while differentiation of function occurred at a fine-grained level of analysis, the brain functioned mainly in an integrated fashion under all circumstances.

Hemispheric asymmetry related to language was especially revealing. The left hemisphere in almost all right handers and most left handers is dominant for language, including speech production, comprehension, semantics and syntax. The right hemisphere, however, simultaneously deals with contextual issues, such as intonation, metaphor and humour.

One must realise that the corpus callosum and other cerebral commissures (white matter connections between the hemispheres) have to play important roles in integrating the function of the two hemispheres. Both inhibitory and excitatory roles have been suggested for the corpus callosum. I have found the mind model of Norman Cook useful in order to explain the integrated functioning of the brain, especially as related to language lateralization. His model deals well with the left and right hemisphere language processing, as described above. In his theory of topographic callosal inhibition, excitation of columns of neurons in the left hemisphere inhibits equivalent columns in the right, but promotes surrounding context-associated processing. The diagram below demonstrates the proposed process. Dark circles represent columns of neurons that are firing. It is quite complex and one really needs to read Cook's paper, or the summary in Springer and Deutsch's book (see at the end of this post).




Cook's brain code, as he called it, is now somewhat dated. I shall welcome newer information that any reader of my blog be aware of.

To conclude, most of the popular left brain right brain ideas are myths - whole-brain half-wittery. The myth-makers, however, at most only pay lip service to that fact. The left brain right brain myth is good for business and they are not about to let science stand in the way of prosperity.

I cannot put it better than Michael Corballis:

"The main difficulty is that reference to the brain can be seen as a legitimizing force that gives scientific credence to dubious practices."

"The problems arise when we allow myth to escape from scientific scrutiny and become dogma, and when dogma creates financial opportunities for charlatans and false prophets. That is what I thinks has happened with the left brain and the right brain."

"Another secret that I can reveal is that lying on the left side enhances left-brain function, while lying on the right side tunes up the right hemisphere. Lying through the teeth is best left to the therapist."

Some useful references:

William CalvinThe throwing madonna: Essays on the brain.
Jeremy Dean Two brains for the price of one?
Cook, N.D. 1984. Callosal inhibition: The key to the brain code. In Behavioral Science. Vol. 29, pp. 98-110.
Harrington, A. 1985. Nineteenth-century ideas on hemisphere differences and "duality of mind". In Behavioral and Brain sciences. Vol. 8, no4, pp. 617-659.
Harris, L. 1985. Teaching the right brain: Historical perspective on a contemporary educational fad. In C.T. Best (Ed.), Hemispheric function and collaboration in the child. Orlando: Academic Press.
Springer, S.P., & Deutsch, G. 1998. Left brain right brain: Perspectives from cognitive neuroscience (5th Ed.). NewYork: W.H. Freeman.
Corballis, M.C. 1999. Are we in our right minds? In S. Della Sala (Ed.), Mind myths: Exploring popular assumptions about the mind and brain. New York: John Wiley & Sons.