Some researchers believe that brain volume may correlate with handedness, although the data on this subject remains controversial. One group of researchers reported that left-handed individuals had a larger brain, while another study found no difference in brain size between the right- and left-handers. As some findings indicate, left-handers are more prone to nighttime awakenings due to sleep disorders caused by periodic limb movements. It seems that left-handed individuals are more likely to experience limb movements while asleep compared to right-handers.
Since handedness has been associated with prenatal hormonal exposure, it could influence the risk of carcinogenesis later in life. Scientists investigated the impact of handedness on brain tumors, both malignant and benign ones. One study examined the associations between glioma, meningioma, and acoustic neuroma with self-reported handedness. Left-handers or ambidextrous (with equal use of both hands) individuals were at reduced risk of glioma (the most common malignant brain tumor) when compared with the right-handers. This relationship was similar for both genders. However, another very recent study found no such association. This large case-control study (which included more than 1000 glioma cases and healthy controls) reported no association between handedness and glioma risk after adjustment for age, gender, and race.
Although the brains of left-handers and right-handers differ in their structures, the available literature shows no noteworthy differences in intelligence as measured by IQ score. Nevertheless, these brain structure differences seem to reflect the more diverse and creative processing of language and emotions by left-handers than by right-handed individuals. This may explain why a greater proportion of left-handers are professional musicians, even in those cases when the musical instruments are designed for right-handers (for example, violins). Similarly, the gift for mathematics seems to be more common in the left-handed populace.
It is obvious that right and left-handers differ not only in hand preference but also in brain structure. This further reflects the ability to perform different tasks and achieve success in different professions. Although there is a clear link between non-right handedness and developmental disorders, there is no association between brain carcinogenesis and the dominance of one hand. It seems that handedness can be predicted in early childhood, even during fetal development, but further investigations are needed to elucidate the origins of our preference to use one hand or the other.
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Corballis, M.C. (2014). Left brain, right brain: facts and fantasies. PLoS Biology. 12(1):e1001767. doi:10.1371/journal.pbio.1001767
Nelson, E.L., Campbell, J.M., Michel, G.F. (2014). Early handedness in infancy predicts language ability in toddlers. Developmental Psychology. 50(3): 809-814. doi:10.1037/a0033803