Wired Differently?: Left-Handedness and the Brain

About 10.6 percent of people are left-handed. It is still not well understood why some people prefer to write, draw, and perform other activities with their left hand, while most people prefer to use their right hand for these things. Recent research about left-handedness has focused on brain differences between left-handers and right-handers.

This makes a lot of sense: Left-handedness is not caused by the hands themselves, but by the differences in brain organization—but which?

Somewhat surprisingly, not much came out of research focused on the size of different brain areas. For example, a large-scale neuroimaging study found no statistically significant differences in the surface area of different brain regions between left- and right-handers (Guadalupe and co-workers, 2014). Only when very liberal statistical thresholds were used, a difference was found in the precentral sulcus, a brain area relevant for motor behavior. These findings suggest that it may not solely be differences in the size of brain areas that make left-handers’ brains different from right-handers’ brains.

A study on handedness and the brain focused on the functional connectome

A recent study on left-handedness and the brain now focused on a different aspect of brain organization: The connections between brain areas. The study, published in the scientific journal eNeuro, was entitled “Functional Connectome Correlates of Laterality Preferences: Insights into Hand, Foot, and Eye Dominance across the Lifespan” (Tejavibulya and co-workers, 2025).

The research team, led by Link Tejavibulya of the Yale School of Medicine, analyzed neuroimaging data from two large publicly available scientific datasets: the Human Connectome Project-Development and the Human Connectome Project-Aging, to investigate brain connections of left- and right-handers over the lifespan. In addition to handedness, they also looked at two other forms of lateral preferences: footedness and eyedness. Overall, data from more than 1,100 volunteers were analyzed, making the findings robust and trustworthy.

Left-handers have some different brain connections than right-handers

The results were quite interesting: The scientists found widespread statistically significant associations between handedness and brain connectivity across the whole brain. In addition to strong links to motor networks in different parts of the brain, left-handedness in particular showed a strong association with the limbic network, which is highly relevant for emotions. The findings for footedness were overall very similar to those for handedness.

Take-away

The study had two important takeaways:

1. First, the connectivity of brain networks related to motor behavior differed between left-handers and right-handers. This was to be expected, as handedness is, after all, a motor preference to perform activities such as writing with one hand and not the other.
2. Second, it showed that left-handedness is not limited to these motor areas, but that there are also connectivity differences in emotion networks (and to a lesser extent other networks) in left-handers compared to right-handers. This is very interesting as it suggests a broader impact of left-handedness on psychological variables, not just a motor preference.