🧠 Left-brain or right-brain: the myth believed by nine out of ten teachers
⏱️ Reading time: 12 minutes
Based on the book: Mente bilingüe. Neurociencia de la lectoescritura (The Bilingual Mind. Neuroscience of Literacy), by Andrés Marín-Palomar. Spanish edition. Coming soon on Amazon.
English edition: The Bilingual Mind. Neuroscience of Literacy, by Andrés Marín-Palomar. Coming soon on Amazon.
Have you ever been told you are a "humanities person" because your right hemisphere is in charge? Have you taken one of those tests that promise to reveal your dominant hemisphere in two minutes? Have you heard a child's reading difficulties explained by saying they are "very right-brained"?
If you answered yes to any of the three, you are not an exception. You are the norm. And that is exactly what makes this neuromyth so hard to dismantle: it does not circulate on the margins; it circulates at the center of the educational system.
In this post, we are going to do three things. First, trace where the idea came from, because it was born from good science. Second, review the study that put it to the test with a thousand people and left it without foundation. And third (what really matters in a classroom or a speech-language pathology clinic), translate all of that into concrete decisions.
✴️ Fun fact
In a study with 242 primary and secondary school teachers, 91% of the British and 86% of the Dutch endorsed this statement: "hemispheric dominance differences (left-brain, right-brain) help explain individual differences among students."
The most uncomfortable part of the study is not that figure, but the next one: teachers who read more science communication scored better on general knowledge about the brain… and at the same time believed more neuromyths, not fewer. Reading a lot of popular science does not vaccinate against error; sometimes it inoculates it (Dekker et al., 2012).
🔍 1. A real origin: the brain is indeed asymmetric
Does this mean everything you have heard is false? No, and that is the trap. The myths that last the longest are those born from a truth and stretched until they break.
Brain asymmetry exists, is well documented, and was described in the 19th century:
- In 1861, the French physician Paul Broca treated a patient who understood everything but could barely articulate a single syllable. The autopsy showed a lesion in the left frontal lobe.
- Shortly after, the German neurologist Carl Wernicke described the reverse pattern: patients who spoke with normal fluency and intonation, but whose sentences meant nothing and who also did not understand what was being said to them. The lesion was also on the left, though further back.
- In the 1960s, Roger Sperry and his student Michael Gazzaniga studied patients with "split brains": people with severe epilepsy whose corpus callosum—the bundle of fibers connecting the two hemispheres—had been severed to prevent seizures from spreading from one side to the other. Without that communication, each hemisphere was isolated, and for the first time it was possible to see what each one resolved on its own.
Sperry received the Nobel Prize in Physiology or Medicine in 1981 for this work, which he shared that year with two vision researchers, David Hubel and Torsten Wiesel. This is worth clarifying because the opposite is often repeated: Gazzaniga, his best-known collaborator and the one who has most popularized these findings, never received the Nobel.
💡 In other words
For more than a century, doctors observed something true: when someone loses speech due to a brain lesion, the lesion is almost always on the left side. And when the cable connecting the two sides was cut in a patient, each side managed different tasks on its own.
So far, solid and proven science. The problem was not what was observed. It was what was deduced afterward.
✴️ Fun fact
Broca's patient was named Louis Victor Leborgne, but he went down in history with the nickname "Tan," because "tan" was the only syllable he could pronounce. Broca did not slice up his brain: he kept it whole in alcohol, convinced that one day there would be better techniques to examine it.
He was right. Leborgne's brain is still kept in Paris, and more than a century and a half later, MRI scans have been performed on it, revealing that the lesion was quite larger and deeper than Broca could see with the naked eye.
⚠️ 2. The false leap: from a handful of patients to a theory of personality
At what exact moment did the reasoning break down?
Not in the data, but in the extrapolation. It went from this statement: "in a brain whose internal communication has been cut, each half solves different tasks," to this other one: "in any healthy person, one half bosses the other around, and that determines how they are and how they learn."
These are two completely different sentences. The first is a surgical observation about a small group of exceptional patients. The second is a theory of personality with no data behind it.
Think about it with a car. The left and right turn signals do different things: that is true and can be checked in any parking lot. But it does not follow from this that there are "left-turn-signal cars"—serious, formal, always turning left—and "right-turn-signal cars," which are more creative. Both turn signals are in the same car, powered by the same circuit, and the car goes where the driver takes it.
💡 In other words
Just because two areas of the brain handle different tasks does not mean one of them governs your personality. Specialization is not the same as dominance.
The liver and the kidneys also do very different things, and no one thinks to say there are "liver people" and "kidney people."
✴️ Fun fact
And what about left-handed people? Do they have language on the other side? Almost never. Cerebral blood flow was measured in 326 healthy people while they generated words, and among the most strongly right-handed, only 4% had language housed in the right hemisphere.
Among the most strongly left-handed, the figure does go up, but only to 27%: nearly three out of four left-handed people have language in the left hemisphere, exactly like the majority of right-handed people. The authors even provided a formula to estimate it: probability of right-hemisphere dominance (%) = 15% − manual laterality (%) / 10 (Knecht et al., 2000).
📊 3. The study that actually measured it: Nielsen et al. (2013)
What if, instead of arguing about it, someone took the trouble to measure it? That is what a team at the University of Utah did.
What they did
- They gathered brain images of 1,011 people between the ages of seven and twenty-nine, from open-access databases.
- They used resting-state functional magnetic resonance imaging (fMRI). Instead of assigning tasks, the brain is recorded while the person is not doing anything concrete, observing which areas activate and deactivate at the same time, spontaneously. It is like looking at background traffic instead of rush hour.
- They divided all gray matter into 7,266 tiny regions and calculated, one by one, the strength of their connection with all the others.
What they found
- There is no "left-brain" profile or "right-brain" profile. Not a single one of the 1,011 people showed a globally more connected network in one hemisphere than the other. The phenotype that sustains the myth simply did not appear.
- Lateralization is local, not global. Clearly lateralized nodes did appear: nine with left-hemisphere predominance (regions of the default mode network and the classic language areas, Broca and Wernicke) and eleven with right-hemisphere predominance (regions of the attentional control network, such as the lateral intraparietal sulcus, anterior insula, MT area, and frontal eye fields).
- Having a highly lateralized node does not drag the rest along. The fact that a person's language was strongly shifted to the left predicted absolutely nothing about the lateralization of the rest of their brain.
💡 In other words
Imagine a city with a thousand neighborhoods. It is true that the central market is on the west side and the bus station on the east side: some functions have a fixed address.
What the study was looking for was something else: people whose entire city had the west side more heavily trafficked than the east side, in all neighborhoods at once. They found none. Not one in a thousand and eleven.
And something more: the fact that the market is on your west side says nothing about where your bus station is. Each function is placed on its own.
✴️ Fun fact
The corpus callosum, the structure severed in Sperry's patients, contains on the order of two hundred million nerve fibers crossing from one hemisphere to the other (Aboitiz et al., 1992).
In other words: while the myth imagines two brains competing, anatomy shows two hundred million cables dedicated exclusively to making sure the two sides talk to each other nonstop. If we were truly "one-hemisphere people," it would be the worst-amortized infrastructure in the human body.
🧭 4. What this study does NOT say
A powerful study also defends itself by marking its limits. These five caveats prevent us from jumping from one myth to another:
- It does not say that the two hemispheres are identical or interchangeable. Functional asymmetry exists and is well established.
- It does not say that lateralization is irrelevant. In epilepsy surgery, in the prognosis of aphasia, or in the presurgical assessment of a tumor, knowing where language is located remains critical information.
- It did not measure personality, creativity, or learning style. It measured resting-state connectivity. What it demonstrates is that the supposed brain substrate of the myth does not exist, not that creativity tests were applied and came out tied.
- It does not address older adults. The sample only goes up to age twenty-nine (mean age 18.3 years), so it does not allow for conclusions about aging.
- Resting state is not the task. Spontaneous connectivity portrays the background architecture well, but it does not equate point-by-point to what happens while someone is reading, calculating, or translating.
✨ 5. What neuroscience says today, function by function
What replaces the dichotomy, then? A less flashy but much more useful idea: distributed networks that collaborate, with local and flexible specializations.
| Cognitive function |
What the myth says |
What neuroscience says |
| Reading and language |
"The left side reads, the right side draws." |
Phonological decoding and visual word recognition show clear left-hemisphere dominance (Dehaene, 2009; Price, 2012). However, global comprehension, prosody, inference, and metaphor require continuous bilateral interaction (Vigneau et al., 2011). |
| Creativity |
"It is exclusively a right-hemisphere thing." |
Creative ability is predicted by the coordinated connection between the default mode network, the executive network, and the salience network, distributed across both hemispheres (Beaty et al., 2018). |
| Bilingualism |
"One language in each hemisphere." |
Both languages share the same control system, with cortical and subcortical components (dorsal anterior cingulate, left prefrontal cortex, left caudate nucleus, inferior parietal lobules). What changes when switching languages is not the hemisphere, but the level of inhibitory control (Abutalebi & Green, 2016). |
| Brain organization |
Binary division: left versus right. |
The cortex is organized along continuous gradients, from primary sensory areas to higher-order transmodal areas. The main axis is not the midline (Margulies et al., 2016). |
💡 In other words
The brain does not work like two bosses dividing up the work. It works like a team of specialists.
When reading aloud, for example, there are left-sided areas in charge of accurately converting letters into sounds, and areas on both sides that handle intonation, double meanings, and understanding why you are being told this. All at once, in the same brain, in milliseconds.
📖 6. Why this matters so much in literacy
Can a neuromyth harm reading acquisition? Yes, and through a very specific pathway: it changes what is taught.
If someone believes that "the left side reads and the right side imagines," they will end up treating decoding and comprehension as two separate, and often rival, subjects: either phonics or reading enjoyment. The evidence says the opposite. Phonological decoding and visual word recognition rely on markedly left-sided circuits (Dehaene, 2009; Price, 2012), while comprehension, prosody, inference, and figurative language systematically recruit the right hemisphere as well (Vigneau et al., 2011). They are not two paths: they are two stretches of the same path.
This has an immediate practical consequence for speech-language intervention. In developmental language disorder (DLD), it is common to find a child who decodes acceptably and yet does not understand what they read, because they fail at inference and figurative language. Treating that as a "hemisphere" problem leads nowhere; treating it as what it is—comprehension that must be taught explicitly—does.
✴️ Fun fact
Writing is a little over five thousand years old. In evolutionary terms, that was yesterday: there has not been enough material time for a "reading area" to emerge through natural selection, and there is no reading gene.
What happens is that the brain recycles. When learning to read, a very specific piece of the left occipitotemporal cortex, which originally served to recognize objects and shapes, is repurposed into a specialized detector for written words. It is known as the visual word form area, and it appears in the same place whether you read in Spanish, English, Hebrew, or Chinese (Dehaene, 2009).
🌐 7. And in bilingualism: one language in each hemisphere?
This is one of the most widespread versions of the myth among families in dual language immersion programs, and it is false.
The two languages of a bilingual person do not live in different hemispheres: they share the same control system, with cortical and subcortical components—dorsal anterior cingulate, left prefrontal cortex, left caudate nucleus, and inferior parietal lobules—that is responsible for selecting one language and inhibiting the other depending on the context (Abutalebi & Green, 2016). When a child switches from Spanish to English in the middle of a sentence, they are not switching hemispheres: they are executing an executive control operation, and they are executing it many times a day.
💡 In other words
Your two languages are not stored in two separate drawers, one on each side of your head. They are in the same closet, and what your brain trains every time you choose one is the person in charge of deciding what to take out and what to leave inside.
That is why being bilingual is not "using half the brain for each language." It is exercising the closet doorkeeper, many times a day, for years.
🎯 8. What to do on Monday: classroom, clinic, and families
Perpetuating supposed "hemispheric learning styles" is not only baseless: it boxes people in. Labels like "I am not creative, I am a science person" or "math is not my thing, I am a humanities person" act as self-fulfilling prophecies. Four concrete changes:
Integrate instead of separating
Design activities that demand both at the same time. In reading comprehension, combine precise decoding with a dramatization, a drawing, or a reformulation that forces the student to construct the inference and the intonation of the text. It is not "technique first, enjoyment later": it is the same thing, in the same session.
Remove deterministic labels
Never tell a student or a family that a child is "left-brained." Replace it with network and plasticity language: "your brain works as a complete network; the more we connect different ways of thinking, the stronger all your connections become." It is more true and, furthermore, it opens doors instead of closing them.
Explain bilingualism as control, not as division
In dual language immersion contexts (Spanish and English, Spanish and Catalan), tell families that alternating languages is not "switching hemispheres," but rather training executive control and the connectivity of the entire network. Incidentally, this deactivates the still-frequent fear that two languages "get in each other's way."
Teach metaphor explicitly
Since figurative language requires bilateral collaboration and is not acquired on its own, work on literal and figurative meaning jointly and explicitly, especially in intervention for DLD and in students learning in their second language.
💡 In other words
Summarized for Monday's faculty meeting: stop classifying children by hemispheres and start giving them tasks that force the brain to coordinate.
The phrase that replaces the myth fits on one line: there are no left-hemisphere or right-hemisphere students; there are networks that get trained.
🧩 In summary
The left-brain/right-brain myth does not survive because it is convincing, but because it is comfortable. It offers an instant explanation for something as complex as why each person is good at a different thing, and it does so with vocabulary that sounds scientific.
But when it is measured—one thousand and eleven brains, 7,266 regions, one by one—the phenotype disappears. What remains is a brain with real local specializations and two hundred million fibers dedicated to ensuring the two sides never stop talking to each other for a single second.
For anyone who teaches reading or intervenes in language, that difference is not an academic nuance. It is the difference between classifying a student and teaching them.
📚 References (APA 7th ed.)
Abutalebi, J., & Green, D. W. (2016). Neuroimaging of language control in bilinguals: Neural adaptation and reserve. Bilingualism: Language and Cognition, 19(4), 689–698. https://doi.org/10.1017/S1366728916000225
Beaty, R. E., Kenett, Y. N., Christensen, A. P., Rosenberg, M. D., Benedek, M., Chen, Q., Fink, A., Qiu, J., Kwapil, T. R., Kane, M. J., & Silvia, P. J. (2018). Robust prediction of individual creative ability from brain functional connectivity. Proceedings of the National Academy of Sciences, 115(5), 1087–1092. https://doi.org/10.1073/pnas.1713532115
Dehaene, S. (2009). Reading in the brain: The new science of how we read. Viking.
Dekker, S., Lee, N. C., Howard-Jones, P., & Jolles, J. (2012). Neuromyths in education: Prevalence and predictors of misconceptions among teachers. Frontiers in Psychology, 3, Article 429. https://doi.org/10.3389/fpsyg.2012.00429
Knecht, S., Dräger, B., Deppe, M., Bobe, L., Lohmann, H., Flöel, A., Ringelstein, E.-B., & Henningsen, H. (2000). Handedness and hemispheric language dominance in healthy humans. Brain, 123(12), 2512–2518. https://doi.org/10.1093/brain/123.12.2512
Margulies, D. S., Ghosh, S. S., Goulas, A., Falkiewicz, M., Huntenburg, J. M., Langs, G., Bezgin, G., Eickhoff, S. B., Castellanos, F. X., Petrides, M., Jefferies, E., & Smallwood, J. (2016). Situating the default-mode network along a principal gradient of macroscale cortical organization. Proceedings of the National Academy of Sciences, 113(44), 12574–12579. https://doi.org/10.1073/pnas.1608282113
Nielsen, J. A., Zielinski, B. A., Ferguson, M. A., Lainhart, J. E., & Anderson, J. S. (2013). An evaluation of the left-brain vs. right-brain hypothesis with resting state functional connectivity magnetic resonance imaging. PLoS ONE, 8(8), Article e71275. https://doi.org/10.1371/journal.pone.0071275
Price, C. J. (2012). A review and synthesis of the first 20 years of PET and fMRI studies of heard speech, spoken language and reading. NeuroImage, 62(2), 816–847. https://doi.org/10.1016/j.neuroimage.2012.04.062
Vigneau, M., Beaucousin, V., Hervé, P.-Y., Jobard, G., Petit, L., Crivello, F., Mellet, E., Zago, L., Mazoyer, B., & Tzourio-Mazoyer, N. (2011). What is right-hemisphere contribution to phonological, lexico-semantic, and sentence processing? Insights from a meta-analysis. NeuroImage, 54(1), 577–593. https://doi.org/10.1016/j.neuroimage.2010.07.036
