Are You Left-Brained or Right-Brained? A Real Finding Turned Into Nonsense

Certain functions are handled predominantly by one hemisphere, and the evidence is solid. Language production and comprehension are strongly left-lateralised in the great majority of people, which was established from the effects of damage to specific left hemisphere regions in the nineteenth century and confirmed by every subsequent method. Processing of faces and of spatial relationships is somewhat right-lateralised. Control of movement and of sensation is crossed, with each hemisphere handling the opposite side of the body, which is the most complete lateralisation of all. Attention to space shows asymmetries, with right hemisphere damage producing neglect of the left side more severely than the reverse. Those findings are not in doubt.

The personality theory asserts things the evidence does not support:

• •That individuals have a dominant hemisphere determining their thinking style
• •That logic, analysis and language sit on one side and creativity, intuition and art on the other
• •That education favours one hemisphere and should be rebalanced
• •That exercises can strengthen the weaker side
• •That personality types map onto hemispheric dominance
• •None of these has support, and the imaging study most often cited against them found no individual dominance

The popular version has a specific origin in genuine research misread. Work in the 1960s and 1970s on patients whose connection between the hemispheres had been surgically cut to control severe epilepsy produced striking findings, since information presented to one hemisphere alone could not be reported verbally when it went to the right, which demonstrated the specialisations dramatically. Roger Sperry shared a Nobel Prize for it in 1981. Popular accounts extended those findings from patients with a severed connection to people whose hemispheres communicate constantly through hundreds of millions of fibres, which is precisely the extension the research does not license. The personality framework was built commercially on top of that, and it has been sold in education and management ever since.

Several comparable claims circulate with the same structure of a real finding stretched past breaking. The assertion that people use ten per cent of their brain has no source in any research and is contradicted by imaging showing activity throughout, by the metabolic cost of the organ and by the fact that damage anywhere produces deficits. Learning styles, meaning that individuals learn better through a preferred sensory channel, is among the most tested claims in education and the tests consistently find no benefit from matching instruction to a stated preference. Claims that particular music improves intelligence rest on a small brief effect on one spatial task that was extended far beyond what it showed. What these share is a plausible mechanism, a commercial market and an appeal to individual difference.

The gap between the real finding and the myth has practical consequences. Teaching methods and training programmes sold on the theory divert time and money and rest on nothing. The framework encourages people to categorise themselves and to avoid activities supposedly belonging to their weaker side, which is the opposite of useful. It also obscures genuinely interesting questions, including why language lateralises at all, why the pattern differs in some left-handed people, how lateralisation develops in childhood, and what happens when a hemisphere is damaged or removed in early life, where the remaining one frequently takes over language substantially. Those questions are active research and are more surprising than any personality typology.

Language is strongly left-lateralised in most people and each hemisphere controls the opposite side of the body, which is established beyond doubt. The personality theory asserting individual dominance and a split between logic and creativity has no support, and imaging studies looking for such dominance found none. It came from extending research on patients whose hemispheres had been surgically disconnected.