How does brain-hemisphere dominance actually work?
Scan a thousand brains looking for the 'left-brained' accountant and the 'right-brained' artist, and you find nobody. The single largest test of the idea found no such thing as a dominant hemisphere.
5 established, 3 disputed, 4 debunked, 2 unresolved. We do not pick an answer; the evidence places each claim. How we decide
45 citations from 15 independent sources - 30 echo the same voices and count once. Graded A1-D1.
Added 3 Jul 2026 - updated 29 Sept 2026
What the four states mean
- Establishedsupported, uncontested
- Disputedcredible sources disagree
- Debunkedrefuted by the evidence
- Unresolvedno settled answer
Established 5supported, uncontested
The two hemispheres work together, and for most tasks both are involved.▰▰▰▱▱ likely3 points
Supports- In reality, for most tasks the two hemispheres work in tandem.Centre for Educational Neuroscience (UCL / Birkbeck): Left brain versus right brain thinkers analysis
- Furthermore, in the normal state the two hemispheres appear to work closely together as a unit, rather than one being turned on while the other idles.Roger W. Sperry, 'Some Effects of Disconnecting the Cerebral Hemispheres', Nobel Lecture (1981), NobelPrize.org authoritative
- The two sides function differently, but they work together and complement each other.Healthline: Left Brain vs. Right Brain: What's the Difference? summary
Testing split-brain patients showed the left hemisphere specialized for language and the right for emotional and nonverbal functions, work that won Roger Sperry the 1981 Nobel Prize.▰▰▰▱▱ likely3 points
Supports- Testing of each disconnected hemisphere again revealed the left to be specialized for language and the right for emotional and nonverbal functionsMichael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
- This work won Roger W. Sperry the Nobel Prize for Physiology and Medicine in 1981Michael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
- Sperry discovered that the left hemisphere of the brain was responsible for language understanding and articulation, while the right hemisphere could recognize a word, but could not articulate it.Embryo Project Encyclopedia (Arizona State University): Roger Sperry's Split Brain Experiments (1959-1968) summary
In Wada testing, bilateral speech representation was found in 15% of non-right-handers without early left-brain injury but was extremely rare in right-handers.▰▰▰▱▱ likely3 points
Supports- Preparatory to craniotomy for the relief of medically refractory focal epilepsy, the lateralization of cerebral speech functions was determined by the Wada intracarotid Amytal test in 134 patients with clinical and radiologic evidence of an early left-hemisphere lesion. Their results were compared with those for 262 patients (140 right-handed, 122 left-handed), who were tested in a similar way.Rasmussen & Milner, 'The role of early left-brain injury in determining lateralization of cerebral speech functions', Ann N Y Acad Sci 299: 355-69 (1977) authoritative
- Bilateral speech representation was demonstrated in 15% of the non-right-handers without early left-brain injury and in 19% of those with evidence of such early injury, whereas it was extremely rare in the right-handed groups.Rasmussen & Milner, 'The role of early left-brain injury in determining lateralization of cerebral speech functions', Ann N Y Acad Sci 299: 355-69 (1977) authoritative
- Handedness and cerebral asymmetry are not only variable, they are also imperfectly related.Michael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
Some brain functions do lean to one side: language tends to be on the left, attention more on the right.▰▰▱▱▱ likely2 points
Supports- "It's absolutely true that some brain functions occur in one or the other side of the brain. Language tends to be on the left, attention more on the right.University of Utah Health Sciences, 'Researchers debunk myth of right-brained and left-brained personality traits' (ScienceDaily, 2013) summary
- The left-lateralized hubs included regions from the default mode network (medial prefrontal cortex, posterior cingulate cortex, and temporoparietal junction) and language regions (e.g., Broca Area and Wernicke Area), whereas the right-lateralized hubs included regions from the attention control network (e.g., lateral intraparietal sulcus, anterior insula, area MT, and frontal eye fields).Nielsen, Zielinski, Ferguson, Lainhart & Anderson, 'An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging', PLOS ONE 8(8): e71275 (2013) authoritative
In a split-brain patient, the left hemisphere explained the left hand's choice in terms consistent with its own knowledge, a process the researchers called 'the interpreter'.▰▰▱▱▱ likely2 points
Supports- When asked why he chose these items, his left hemisphere replied ‘Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed’. Here the left brain, observing the left hand’s response, interprets that response in a context consistent with its sphere of knowledgeMichael S. Gazzaniga, 'Cerebral specialization and interhemispheric communication: Does the corpus callosum enable the human condition?', Brain 123 (2000) authoritative
- We called this left hemisphere process ‘the interpreter’Michael S. Gazzaniga, 'Cerebral specialization and interhemispheric communication: Does the corpus callosum enable the human condition?', Brain 123 (2000) authoritative
Disputed 3credible sources disagree
Cutting the connections between the hemispheres creates two independent conscious systems in one brain.▰▰▰▱▱ likely1 against3 points
Supports- In Sperry’s words, each brain hemisphere is “. . . indeed a conscious system in its own right, perceiving, thinking, remembering, reasoning, willing, and emoting, all at a characteristically human level, and . . . both the left and the right hemisphere may be conscious simultaneously in different, even in mutually conflicting, mental experiences that run along in parallel.”Drawing on the Right Side of the Brain (official website of Betty Edwards): Theory primary
- Each disconnected hemisphere behaved as if it were not conscious of cognitive events in the partner hemisphereRoger W. Sperry, 'Some Effects of Disconnecting the Cerebral Hemispheres', Nobel Lecture (1981), NobelPrize.org authoritative
Against- These findings suggest that severing the cortical connections between hemispheres splits visual perception, but does not create two independent conscious perceivers within one brain.Pinto et al., 'Split brain: divided perception but undivided consciousness', Brain 140(5): 1231-1237 (2017) authoritative
Creativity is lateralized to the right hemisphere.▰▰▰▱▱ roughly even chance1 against2 points
Supports- Creativity also seems to be right dominant, possibly due to a dependence in creative thinking on global processing and taking context into accountCentre for Educational Neuroscience (UCL / Birkbeck): Left brain versus right brain thinkers analysis
Against- One popular example is Betty Edwards' Drawing on the Right Side of the Brain , first published in 1979 but now in its fourth edition [7] , which epitomizes the popular view that the right hemisphere is responsible for creativity. Brain imaging shows, though, that creative thought activates a widespread network, favoring neither hemisphereMichael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
The differing world views of the right and left brain have shaped Western culture since Plato.▰▰▰▱▱ unlikely2 against3 points
Supports- The differing world views of the right and left brain (the "Master" and "Emissary" in the title, respectively) have, according to the author, shaped Western culture since the time of the ancient Greek philosopher PlatoThe Master and His Emissary - Wikipedia summary
Against- Although widely acclaimed, this book goes far beyond the neurological facts.Michael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
- "the findings of brain science are nowhere near fine-grained enough yet to support the large psychological and cultural conclusions Iain McGilchrist draws.The Master and His Emissary - Wikipedia summary
Debunked 4refuted by the evidence
Conventional wisdom holds that people are either right-brained (intuitive and creative) or left-brained (quantitative and analytical), with one side of the brain more dominant.Refuted by
Lateralization of brain connections appears to be a local rather than global property of brain networks, and our data are not consistent with a whole-brain phenotype of greater “left-brained” or greater “right-brained” network strength across individuals.
refuted3 against7 pointsThe claim rested on- According to conventional wisdom, people tend to have a personality, thinking style, or way of doing things that is either right-brained or left-brained.Robert H. Shmerling, 'Right brain/left brain, right?', Harvard Health Blog analysis
- Those who are right-brained are supposed to be intuitive and creative free thinkers.Robert H. Shmerling, 'Right brain/left brain, right?', Harvard Health Blog analysis
- Meanwhile, left-brained people tend to be more quantitative and analytical.Robert H. Shmerling, 'Right brain/left brain, right?', Harvard Health Blog analysis
- The theory that you’re either left-brained or right-brained suggests that one side of your brain is more dominant.Healthline: Left Brain vs. Right Brain: What's the Difference? summary
Refuted by- Lateralization of brain connections appears to be a local rather than global property of brain networks, and our data are not consistent with a whole-brain phenotype of greater “left-brained” or greater “right-brained” network strength across individuals.Nielsen, Zielinski, Ferguson, Lainhart & Anderson, 'An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging', PLOS ONE 8(8): e71275 (2013) authoritative
- But people don't tend to have a stronger left- or right-sided brain network. It seems to be determined more connection by connection,University of Utah Health Sciences, 'Researchers debunk myth of right-brained and left-brained personality traits' (ScienceDaily, 2013) summary
- The authors concluded that the notion of some people being more left-brained or right-brained is more a figure of speech than an anatomically accurate description.Robert H. Shmerling, 'Right brain/left brain, right?', Harvard Health Blog analysis
Left-handed people are more creative than right-handers.Refuted by
“The data do not support any advantage in creative thinking for lefties,” said Daniel Casasanto
refuted2 againstsummary-sourced3 pointsThe claim rested on- What do Leonardo da Vinci, M.C. Escher and Jimi Hendrix have in common? They’re just a few of the creative geniuses also known for being left-handed, helping to fuel the widespread belief that lefties are more creative.Cornell Chronicle: Why are lefties more creative? Turns out, they're not (2025) summary
Refuted by- “The data do not support any advantage in creative thinking for lefties,” said Daniel CasasantoCornell Chronicle: Why are lefties more creative? Turns out, they're not (2025) summary
- After reviewing nearly 1,000 studies, researchers found no consistent advantage in creative thinking for leftiesNeuroscience News: Left-Handed Creativity Myth Debunked (2025) summary
Differences in hemispheric dominance (left brain, right brain) help explain individual differences among learners.Refuted by
However, people don’t show a general dominance of one or other hemisphere.
refuted3 against4 pointsThe claim rested on- The most prevalent of these myths were (1) “Individuals learn better when they receive information in their preferred learning style (e.g., auditory, visual, kinesthetic)”, (2) “Differences in hemispheric dominance (left brain, right brain) can help explain individual differences amongst learners”, and (3) “Short bouts of co-ordination exercises can improve integration of left and right hemispheric brain function”. More than 80% of the teachers believed these myths.Dekker, Lee, Howard-Jones & Jolles, 'Neuromyths in Education: Prevalence and Predictors of Misconceptions among Teachers', Frontiers in Psychology 3:429 (2012) authoritative
Refuted by- However, people don’t show a general dominance of one or other hemisphere.Centre for Educational Neuroscience (UCL / Birkbeck): Left brain versus right brain thinkers analysis
- In the classroom the left brain/right brain myth has resulted in the development of the ‘whole-brain learning’ approach, which involves trying to balance processing in the two hemispheres by including both analytical and creative aspects in a task. In a way this is all very well, as varying teaching methods may keep students attending longer, providing more opportunities to learn material, but the approach is not based on good science.Centre for Educational Neuroscience (UCL / Birkbeck): Left brain versus right brain thinkers analysis
- Polarities of left and right brain are broadly invoked in art, business, education, literary theory, and culture, but owe more to the power of myth than to the scientific evidenceMichael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
The popular left-brain versus right-brain split in thinking is grounded in Roger Sperry's Nobel Prize-winning split-brain research.Refuted by
The left-right dichotomy in cognitive mode is an idea with which it is very easy to run wild.
refuted3 against5 pointsThe claim rested on- The teaching methods of Dr. Edwards drew on the Nobel Prize-winning work of Dr. Roger W. SperryDrawing on the Right Side of the Brain (official website of Betty Edwards): Theory primary
- To apply Roger Sperry’s research to the problem of learning to draw, Betty Edwards needed to find ways to bypass the verbal L-mode systemDrawing on the Right Side of the Brain (official website of Betty Edwards): Theory primary
Refuted by- The left-right dichotomy in cognitive mode is an idea with which it is very easy to run wild.Roger W. Sperry, 'Some Effects of Disconnecting the Cerebral Hemispheres', Nobel Lecture (1981), NobelPrize.org authoritative
- Furthermore, in the normal state the two hemispheres appear to work closely together as a unit, rather than one being turned on while the other idles.Roger W. Sperry, 'Some Effects of Disconnecting the Cerebral Hemispheres', Nobel Lecture (1981), NobelPrize.org authoritative
- This work won Roger W. Sperry the Nobel Prize for Physiology and Medicine in 1981, but again led to speculation, most of it exaggerated or ill-founded, about the complementary functions of the two sides of the brain.Michael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
Unresolved 2no settled answer
Why the human brain is so laterally specialized, and which genes are responsible, is not settled.▰▰▰▱▱ likely2 points
Supports- Nowhere in the animal kingdom is there such rampant specialization of function. Why is this, and how did it come about? What emerges from split-brain research is a possible insight to these questions.Michael S. Gazzaniga, 'Cerebral specialization and interhemispheric communication: Does the corpus callosum enable the human condition?', Brain 123 (2000) authoritative
- Handedness and brain asymmetry are inborn and under partial genetic control, although the gene or genes responsible are not well established.Michael C. Corballis, 'Left Brain, Right Brain: Facts and Fantasies', PLOS Biology 12(1): e1001767 (2014) analysis
Whether greater left lateralization of one brain network goes with greater right lateralization of another within individuals is not settled.▰▰▰▱▱ roughly even chance1 against3 points
Supports- Additionally, it is unknown how the lateralization of one functional network may affect the lateralization of other networks within individuals.Peterson et al., 'Evidence for a compensatory relationship between left- and right-lateralized brain networks', Imaging Neuroscience 3 (2025) authoritative
- We found general support for a dependent relationship between highly left- and right-lateralized networks, meaning that across subjects, greater left lateralization of a given network (such as a language network) was linked to greater right lateralization of another network (such as a ventral attention/salience network) and vice versa.Peterson et al., 'Evidence for a compensatory relationship between left- and right-lateralized brain networks', Imaging Neuroscience 3 (2025) authoritative
Against- Connections involving only left- or only right-lateralized hubs showed positive correlation across subjects, but only for connections sharing a node. Lateralization of brain connections appears to be a local rather than global property of brain networksNielsen, Zielinski, Ferguson, Lainhart & Anderson, 'An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging', PLOS ONE 8(8): e71275 (2013) authoritative
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