Left- and right-handers share similarities in the brain when it comes to numbers

Western University

Celia Goffin

Left- and right-handers may write with different hands, but the brain processes numbers the same way for both. This is according to a new study from Western University.


For this Western study, the researchers focused on left-handers to determine if lefties learned to use a different area of their brain to process numbers.

In a Registered Report, supported in part by BrainsCAN, Western researchers Celia Goffin, Moriah Sokolowski, Michael Slipenkyj and Daniel Ansari found the location in the brain for processing numbers is the same for both right- and left-handed individuals.

“We studied a group of left-handed participants and a group of right-handed participants and compared their brain activation during a symbolic number task and we didn’t find any differences between the groups,” says Goffin, a Western PhD student in Developmental Psychology and first author of the study.”

With only 10 per cent of the world’s population identified as left-handed, previous studies typically relied on right-handed participants to learn how the brain processes numbers. For this study, the researchers focused on left-handers to determine if lefties learned to use a different area of their brain to process numbers.

“The study replicated previous results from only right-handers showing a left-lateralized response to symbolic numbers in the brain,” says Ansari, Principal Investigator at Western’s Numerical Cognition Lab and senior author of the study. “In this study, we thought we might find that right-handers recruit the left side of their brain while left-handers use the right side of their brain for numbers, but it turns out this was not the case.”

The brain’s ability to understand that a number represents a quantity is processed in a specific region of the brain known as the intraparietal sulcus (IPS). When a person is viewing numbers, the left IPS becomes activated. Understanding why it’s activated on the left side of the brain as opposed to the right side, or a combination of both, is an area that researchers are still investigating.

“When you’re a kid learning numbers, you’re practicing them, tracing them and drawing numbers over and over again,” explains Goffin. “Our hypothesis was this practice and process in some way shapes how numbers are represented in the brain.”

For the study, Goffin used functional magnetic resonance imaging (fMRI) to compare brain activation of right- and left-handed participants while they observed numbers.

“We did not find differences between the left- and right-handers when they were compared,” says Ansari, a core member of Western’s Brain and Mind Institute. “These data suggest that handwriting experience cannot explain why symbolic numbers are processed in the brain’s left hemisphere.”

How the brain is able to take arbitrary symbols and assign meaning to them in the form of numbers is a major question for developmental psychologists. By exploring this question, it could eventually assist in developing interventions for children who have difficulties forming these representations of numbers.

This study is the first Registered Report by Ansari’s team. The full paper will be published in the journal Cortex later this year. Registered Reports are studies that are peer-reviewed before the study is conducted and data collected, with the goal of improving the methodology and analysis plan of the proposed study and reducing bias for statistically significant, positive results.

“The peer review process for a Registered Report is different from conventional article formats,” says Ansari. “It reduced the emphasis on results and instead focused on the whole research process from start to finish.”

MEDIA CONTACT: Jeff Renaud, Senior Media Relations Officer, 519-661-2111, ext. 85165, 519-520-7281 (mobile), jrenaud9@uwo.ca, @jeffrenaud99

Western University delivers an academic experience second to none. Since 1878, The Western Experience has combined academic excellence with life-long opportunities for intellectual, social and cultural growth in order to better serve our communities. Our research excellence expands knowledge and drives discovery with real-world application. Western attracts individuals with a broad worldview, seeking to study, influence and lead in the international community.

BrainsCAN is Western University’s research initiative in cognitive and behavioural neuroscience that aims to transform the way brain diseases and disorders are understood, diagnosed and treated. https://brainscan.uwo.ca/


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Celia Goffin
Celia Goffin
For this Western study, the researchers focused on left-handers to determine if lefties learned to use a different area of their brain to process numbers.