There are no left-brained or right-brained people — but the brain really is lateralized, and the difference between those two sentences is the whole story. Particular functions do sit more on one side than the other. What has never been found is a person whose brain runs on one hemisphere, or a link between a supposed dominant side and being logical or creative.
Quick answer
Lateralization is real. In most people language is handled mainly on the left; attention and some spatial processing lean right. Hemispheric dominance as a personality type is not. When Nielsen and colleagues examined 1,011 brains aged 7 to 29 across 7,266 regions, they found lateralized networks but no individuals with a globally stronger side. Their conclusion: “an individual brain is not ‘left-brained’ or ‘right-brained’ as a global property”.
What each hemisphere actually does
The real asymmetries are narrower and less flattering than the popular version. They are about specific operations, not about outlook.
| Hemisphere | Leans towards | What that does not mean |
|---|---|---|
| Left | Speech production and grammar in most people; sequencing; control of the right side of the body | Being an analytical or organised kind of person |
| Right | Aspects of visual and spatial processing, face recognition, the emotional tone of speech; control of the left side of the body | Being a creative or intuitive kind of person |
Both columns describe tendencies in a population, not switches. The hemispheres are joined by the corpus callosum and trade information continuously, so ordinary tasks — reading a sentence, following a conversation, finding your car — run across both.
Where the idea came from: the split-brain patients
It began with real science. In the 1960s Roger Sperry and colleagues studied a small number of patients whose corpus callosum had been cut to control severe epilepsy. With the connection severed, the hemispheres could be tested separately, and they behaved differently — most strikingly, information presented only to the right hemisphere could not be described in words. Sperry received the 1981 Nobel Prize in Physiology or Medicine, “for his discoveries concerning the functional specialization of the cerebral hemispheres”.
The leap happened afterwards, outside the laboratory. Findings about disconnected hemispheres in a handful of surgical patients were retold as a claim about intact brains in the general population, and then as a claim about personality. Michael Corballis, reviewing the field for PLoS Biology in 2014, set out precisely this distinction between the documented asymmetries and what he called the fantasies built on top of them.
What happened when the popular claim was tested
The claim is testable, and it was tested. Nielsen, Zielinski, Ferguson, Lainhart and Anderson used resting-state functional connectivity MRI on 1,011 people aged 7 to 29, dividing grey matter into 7,266 regions and asking whether individuals differ in how strongly their left-sided or right-sided networks are connected.
They found what the anatomy predicts: hubs that are genuinely lateralized, language regions among them. They did not find what the popular theory predicts. There was no group of people with a globally stronger left network, and no group with a stronger right one — the variation that does exist is local, not whole-brain. A person can have a strongly left-lateralized language system and nothing else about them leaning left at all.
Even language is not lateralized in everyone
The strongest real asymmetry has exceptions, and they are common enough to matter. Knecht and colleagues measured hemispheric language dominance in 326 healthy volunteers using functional transcranial Doppler sonography and found right-hemisphere language dominance in 4% of strong right-handers — rising steadily with left-handedness to 27% of strong left-handers.
So roughly one left-hander in four has language on the side the textbook diagram calls the wrong one, and is in every other respect unremarkable. If the single best-established lateralization varies this much between healthy people, a whole personality built on hemispheric dominance was never a safe inference.
Why the idea is still everywhere
Because it is taught. Macdonald, Germine, Anderson, Christodoulou and McGrath surveyed 3,877 people in 2017 — 3,045 members of the general public, 598 educators and 234 people with substantial neuroscience training — on the statement “Some of us are ‘left-brained’ and some are ‘right-brained,’ and this helps explain differences in learning”. It was endorsed by 64% of the public, 49% of educators and still 32% of those with the most neuroscience exposure.
Teacher surveys elsewhere find the same belief at very different strengths, which is itself worth knowing:
- United Kingdom — 91% of 137 teachers, and the Netherlands — 86% of 105 teachers, agreed that hemispheric dominance helps explain differences between learners (Dekker and colleagues, 2012).
- Spain — 67.2% of 284 teachers, with only 10.2% answering correctly and 22.5% saying they did not know (Ferrero, Garaizar and Vadillo, 2016).
- Greece — 55% of 573 trainee teachers, with 7.9% correct and 37.1% unsure (Papadatou-Pastou, Haliou and Vlachos, 2017).
Two things follow. The belief is not universal, so it is not simply how people naturally think — it tracks what a particular school system taught. And more training reduces it without removing it.
Is there a left brain right brain test?
Not one that measures anything. The online quizzes, the spinning-dancer animation and the colour tests are entertainment; they record your answers or your visual interpretation, neither of which is a measure of hemispheric activity. Establishing which side handles language in an individual takes imaging or Doppler sonography in a clinical setting, is done for reasons such as planning surgery, and still tells you only where language sits.
This matters more than it sounds, because the label gets attached to children and then to their choices — a right-brained child steered away from mathematics, a left-brained one told they are not the creative one. The evidence does not support either instruction.
Hemispheres, intelligence and IQ
Brain-side labels are one of a family of ideas that sort people into cognitive types. The learning styles claim does it by preferred format, the types of intelligence debate does it by domain of ability, and left-brain/right-brain does it by hemisphere. All three are more appealing than the evidence behind them, and the first and third have both failed direct testing.
An IQ test measures something narrower and better defined: reasoning, verbal and numerical problem-solving, working memory and processing speed, reported as a number on the IQ scale. It does not tell you which hemisphere you favour, because that is not a thing a person has. If the question underneath the brain-side quiz is really whether you can get sharper, that page collects what the evidence supports.
Trust and scope notes
This page is educational. It is not diagnostic and not clinical advice. Hemispheric lateralization is genuinely assessed in medicine — before neurosurgery, or after a stroke — and nothing here describes or replaces that process.
IQ Revealed is not affiliated with, endorsed by or connected to the Nobel Foundation, the estate of Roger Sperry, or any of the universities, journals or research groups named on this page. They are named so that each claim can be traced to the work that made it. Quoted phrases are taken from the published abstracts of the papers linked in the sources and from the Nobel Foundation's own statement of the award.