Are left-handers more synchronized than right-handers?

You should remember that one left-handed colleague in school that used to complain about how some daily activities were harder for him, such as “keeping their hands clean” because they smudged the ink while writing, or cutting paper as it was hard to use scissors properly. Or maybe you are this person yourself.

Around 1860 left handed people were seen as “being in the league with the devil” as if they were cursed. Nowadays, nearly 12% of the world, with a higher incidence in men, is left-handed.

Although the reasons for left-handedness continue not totally unraveled, it is assertive to say that genes play a role in it along with other factors such as environmental ones. During the past years, many molecular and neurological studies, mainly associated with cerebral laterality, have been performed regarding this issue.

Wiberg et al., (2019) studied DNA of 400,000 people, from which 38,332 left-handers. More specifically, they isolated 4 genetic regions associated with left-handedness. Genes from 3 of those regions are linked to proteins that are connected with microtubules, thus influencing brain structure.

Figure 1. Brain Areas. Source: Brett Szymik, (2011).

Before further discussion beholding cerebral variations due to handedness, it is important to remember that the left side of the body is controlled by the right side of the brain and vice versa. Taking that into consideration, it has been demonstrated that handedness shows differences regarding brain regions and functional hemispheric assymetries. For example, according to Germann et al., (2019) and Schmitz et al. (2019), the motor cortex in the right side of the brain of left-handers is dominant for precise motor behavior, such as writing, and bigger. The contrary is applicable for right-handers. Additionally, left-handed people exhibit a weaker left linguistic-specific lateralization for written language generation compared to right-handers.

It is noticeable among several studies that the cerebral asymmetries observed in right-handers are stronger than in left-handers. Johnstone et al., (2021) presented data obtain from MRI (Magnetic Resonance Imaging) and four-condition localizer (to study brain activation) which suggest a reduced hemispheric specialization in left-handers for verbal fluency, and body and face processing.

As a matter in fact, left-handed people have an overall higher brain synchronization and it is known that there is a slightly higher incidence of schizophrenia among left-handed people, in contrast to Parkinson’s disease.

References Akira Wiberg, Michael Ng, Yasser Al Omran, Fidel Alfaro-Almagro, Paul McCarthy, Jonathan Marchini, David L Bennett, Stephen Smith, Gwenaëlle Douaud, Dominic Furniss, Handedness, language areas and neuropsychiatric diseases: insights from brain imaging and genetics, Brain, Volume 142, Issue 10, October 2019, Pages 2938–2947, https://doi.org/10.1093/brain/awz257

Brett Szymik. (2011, May 09). What's Your Brain Doing?. ASU - Ask A Biologist. Retrieved July 27, 2022 from https://askabiologist.asu.edu/brain-regions

Germann, J., Petrides, M. & Chakravarty, M.M. Hand preference and local asymmetry in cerebral cortex, basal ganglia, and cerebellar white matter. Brain Struct Funct 224, 2899–2905 (2019). https://doi.org/10.1007/s00429-019-01941-6

Johnstone LT, Karlsson EM, Carey DP. Left-Handers Are Less Lateralized Than Right-Handers for Both Left and Right Hemispheric Functions. Cereb Cortex. 2021 Jul 5;31(8):3780-3787. doi: 10.1093/cercor/bhab048. PMID: 33884412; PMCID: PMC8824548.

Papadatou-Pastou M, Sampanis P, Koumzis I, Stefanopoulou S, Sousani D, Tsigkou A, Badcock NA. Cerebral laterality of writing in right- and left-handers: A functional transcranial Doppler ultrasound study. Eur J Neurosci. 2022 Jul;56(2):3921-3937. doi: 10.1111/ejn.15723. Epub 2022 Jun 14. PMID: 35636946.

Schmitz J, Güntürkün O, Ocklenburg S. Building an Asymmetrical Brain: The Molecular Perspective. Front Psychol. 2019 Apr 30;10:982. doi: 10.3389/fpsyg.2019.00982. PMID: 31133928; PMCID: PMC6524718.