Left-Handedness and Brain Asymmetries: How Are They Linked?
Left-handers show different brain asymmetries than right-handers.
Posted December 22, 2025 | Reviewed by Michelle Quirk
Around the world, 10.6 percent of people are left-handed. Handedness is a form of so-called functional brain asymmetry: left-right differences in brain function. In left-handers, the right motor cortex is dominant for conducting fine motor tasks like writing, as the left half of the brain controls the right side of the body, and the right side of the brain controls the left side of the body. In right-handers, it is the other way around. For them, the left half of the brain is dominant for fine motor skills. There are also many other functional asymmetries in the human brain. For example, in most (but not all) people, the left half of the brain is dominant for processing language, while the right half of the brain is dominant for processing faces. Since handedness represents a form of functional brain asymmetry, it could be asked whether left-handers also show changes in other forms of brain asymmetries compared to right-handers.
A breakthrough neuroimaging study on handedness and brain asymmetries
An interesting neuroimaging study from 2021 provided an answer to this question. In the study, conducted by scientists Leah Johnstone, Emma Karlsson, and David Carey, 33 right-handers and 58 left-handers were put into an MRI scanner to create images of their brains while they performed several different tasks ( Johnstone and co-workers, 2021 ). These tasks included a verbal fluency paradigm in which the volunteers had to silently create words starting with the letter “A” in their brains. This task was used to determine the language-dominant half of the brain (in most people, this would be the left half of the brain). Moreover, the volunteers had to view pictures of faces, bodies, and scenes while their brain activity was assessed with the scanner. For each of the four tasks, the scientists determined for each volunteer whether they showed a left-sided or a right-sided dominance and how strong this asymmetry was by calculating a so-called laterality index for each task. The laterality ranges from −1 (only the right half of the brain is active) to +1 (only the left half of the brain is active).
What did the scientists find out?
The statistical analysis of these data showed that left-handers indeed showed differences in brain asymmetries compared to right-handers. On average, volunteers showed a left-hemispheric dominance for processing language and a right-hemispheric dominance for processing faces, bodies, and scenes. These findings were in line with previous studies on brain asymmetries. Interestingly, left-handers showed significantly reduced asymmetries in all four tasks compared to right-handers. So they had less leftward language dominance and less rightward dominance for processing faces, bodies, and scenes.
Left-handers show an unusual right-hemispheric dominance for fine motor tasks compared to the much more common left-hemispheric dominance for fine motor tasks observed in right-handers. The study suggests that they are also more likely to show unusual patterns for other forms of brain asymmetries, including language and processing of faces, bodies, and scenes. This suggests a link between handedness and other forms of brain asymmetries.
Johnstone, L. T., Karlsson, E. M., & Carey, D. P. (2021). Left-Handers Are Less Lateralized Than Right-Handers for Both Left and Right Hemispheric Functions. Cerebral Cortex (New York, N.Y. : 1991) , 31 (8), 3780–3787. https://doi.org/10.1093/cercor/bhab048
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Sebastian Ocklenburg, Ph.D., is a professor for research methods in psychology at the Department of Psychology at MSH Medical School in Hamburg, Germany. His research focuses on left-handedness and brain asymmetries.
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