Left-Brained or Right-Brained? Why It Is a Myth

You have probably seen the quiz. A handful of questions about whether you prefer maths or painting, lists or daydreams, and then the verdict: you are left-brained, logical and analytical, or right-brained, creative and intuitive.

It is one of the most durable ideas in popular psychology, and not only among quiz-takers. In 2012, Sanne Dekker and colleagues surveyed 242 teachers in the United Kingdom and the Netherlands who were interested in neuroscience. The statement that differences in hemispheric dominance - left brain, right brain - help explain differences between learners was accepted by 91% of the British teachers and 86% of the Dutch ones.

The idea is not pure invention. It grew out of some of the most famous experiments in the history of neuroscience. But somewhere between the laboratory and the quiz, it changed into something the research never said.

Where the idea came from

In the 1960s, Roger Sperry, Joseph Bogen and a young Michael Gazzaniga began studying patients whose corpus callosum - the thick bundle of fibres that connects the two halves of the brain - had been cut to control severe epilepsy. With the connection gone, the researchers could show information to one hemisphere at a time and see what each could do on its own.

The results were striking. In most of these patients, the left hemisphere handled speech: shown a word or an object, it could name it. The right hemisphere often could not put a name to what it saw, but could still recognise it and point to it with the left hand. Other tasks, such as some kinds of spatial processing, showed the opposite pattern.

This work helped establish hemispheric specialisation, and in 1981 Sperry shared the Nobel Prize in Physiology or Medicine for it. Writing in 2005 about forty-five years of split-brain research, Gazzaniga stressed two themes: specialisation, and integration - the way the two halves, when connected, work together.

The popular version kept the first theme and dropped the second. It also made a leap the research never made: from "some functions rely more on one side" to "some people rely more on one side".

The 2013 test

That leap is testable. If there really are left-brained and right-brained people, their brain networks on one side should be stronger across the board.

In 2013, Jared Nielsen, Jeffrey Anderson and colleagues at the University of Utah analysed resting-state brain scans from 1,011 people aged 7 to 29. They divided the brain into 7,266 regions and measured, for each person, how lateralised the connections between them were.

They did find lateralisation. There were clear hubs on the left, including language areas such as Broca's and Wernicke's areas, and clear hubs on the right, including regions involved in controlling attention. But when they looked at individuals, a person with strongly left-lateralised connections in one network was not more left-lateralised overall. Lateralisation turned out to be a local property of specific networks, not a whole-brain trait. The authors wrote that their data were not consistent with a "left-brained" or "right-brained" phenotype.

It is one study, based on the brain at rest rather than during creative or logical tasks, and absence of evidence is not proof. But it tested the popular claim directly with a large sample, and the claim did not show up.

What specialisation really looks like

Specialisation is real, but it is messier and more interesting than the quiz suggests.

Take language, the most lateralised function we know. In 2000, Stefan Knecht and colleagues measured language dominance in 326 healthy people. Right-hemisphere dominance for language appeared in 4% of strong right-handers, 15% of ambidextrous people and 27% of strong left-handers. So even for language, "left" is the usual pattern rather than a rule, and it varies in ways that have nothing to do with personality.

And the things the myth assigns to one side - logic, creativity, intuition - are not single functions at all. Writing a story involves language, memory, imagery, planning and judgement. Solving a maths problem involves spatial reasoning, working memory and language. Complex thinking draws on networks spread across both hemispheres, linked through the corpus callosum that the split-brain patients had lost.

The Dekker survey found something else worth noting: teachers who knew more general facts about the brain were, if anything, more likely to believe the neuromyths. Knowing a little neuroscience can make a myth more convincing, because it sounds like the real thing.

What this means for you

None of this means people think alike. Differences in thinking style are real and measurable. The mistake is to explain them with brain hemispheres rather than describing them directly.

• Describe the preference, not the hemisphere. Some people enjoy effortful thinking more than others, a trait psychologists call need for cognition. Some prefer to work with images and diagrams, others with words. Those are real differences, and our need for cognition and visual-verbal tests measure them without pretending to scan your brain.
• Creativity is not one thing. People can be creative in writing, science, craft or everyday problem-solving, and being strong in one domain says little about another. Our creativity domains test looks at that spread.
• Be wary of any claim that sorts you by brain side. It is a sign the product is using neuroscience vocabulary without neuroscience evidence.
• Do not let a label limit you. Believing you are "not a logical person" because of a quiz result is the most harmful part of the myth. Skills in maths, language and art all improve with practice, whatever you were told about your brain.