From our early days in elementary school we learn about this notion of “Left Brain” and “Right Brain.” The idea was that our “Left Brain” was analytical and important for data driven thought. Those who were more “Left Brain focussed” enjoyed mathematics and science. The “Right Brain” was seen as this hub for creativity and art. People who were more “Right Brain focussed” were said to engage in theatre, painting, and literature. As interesting of a concept as this might be, it is largely false. While this does touch upon the important idea of region specific specialization in the brain, the true story is much more complicated. Today we are going to break down the actual differences between the right hemisphere and left hemisphere of the brain!
Let’s start with a little bit of neuroanatomy. The brain is split into two hemispheres, the left hemisphere and the right hemisphere. While these two portions of the brain are “separated” they are connected by a large band of neural tissue called the corpus callosum. This structure allows for easy communication between the 2 hemispheres, making them essentially 1 unit (Rosen, 2018). The concept that these 2 hemispheres contained structures that served different functions originated from our understanding of right-handedness.
Over 90% of people report being right-handed. Historical evidence shows that preference for the right hand has existed for the entirety of human history (Price, 2021)! Through neuroscientific experimentation scientists discovered that the movement centers of the brain seemed to control the opposite sides of the body (left hemisphere controls right side of the body and vice versa). As experimentation and stroke studies (studying the behavior in patients who have had a stroke that damaged specific portions of their brain) became more robust the connection between the brain and handedness came more into focus (Corballis, 2017).
In the mid to late 1800s several scientists published data suggesting that the production and comprehension of language are carried out by structures in the left hemisphere of the brain for most individuals (Corballis, 2014; Javed et al., 2020). In the 1950s, Roger Sperry began his research on what he called “Split-Brain” patients. These were patients who had severe epilepsy that required the lesioning of the corpus callosum in order to treat. These patients possessed both working hemispheres of their brain, but lacked the structure meant to share signals between them, making them functionally operate separately. While you might imagine that these patients would have serious deficits, they actually functioned relatively normally. Gazzaniga, an acclaimed researcher that worked in Sperry’s lab, found that the deficits became apparent when these patients were asked to look at images in their left visual field and tell the researchers what they saw. Split-brain patients were consistently unable to name things that they saw in their left visual field, while fully able to name things they saw in their right visual field (Gazzaniga & Sperry, 1965; Lienhard, 2017). The question is why?
Well, things that you see in your left visual field are processed by your right hemisphere, while things that you see in your right visual field are processed by your left hemisphere. Remember that the left hemisphere contains the centers responsible for language. Since the hemispheres of split-brain patients cannot communicate with each other, visual information sent to the right hemisphere cannot be spoken or written about because it is isolated from the language centers of the brain (Gazzaniga & Sperry, 1965; NPR, 2017)! So what does this have to do with handedness? Well, the working theory on differences in handedness comes from the location of the language centers of the brain. For most people these language centers are isolated to the left hemisphere. Because of this, it is easiest for their right hand to produce written language because it is most heavily wired to the left hemisphere (as we discussed earlier). The preference for using the right hand to write trains the body and the brain to rely more on the right hand, making it the dominant one. For individuals who are left-handed, the theory is that their language centers are isolated to the right hemisphere of their brain, causing a preference for the left hand, however it is important to note that it is likely more complicated than this (as many left-handed individuals show normal left side lateralization for speech) (Scientific American, 2004; NPR, 2017).
Years of neuropsychological testing and brain imaging has led scientists to put to rest the traditional idea of “Right brian for art and creativity and left brain for analytics.” Both hemispheres of our brain are activated simultaneously for most activities and thoughts we engage in. That said, lateralization is a real thing! Generally speaking, the left hemisphere is more involved with language while the right hemisphere is more involved in visuospatial ability (Gotts et al., 2013). This is important to understand because as Sal Khan so beautifully puts it, all humans are naturally curious. You should never feel boxed-in to either the liberal arts or the sciences. There is science and math in art and literature just as there is creativity and art in science and math!
