Tuesday 12 November 2019

Left brain versus right brain myth

In popular culture there are a lot of myths surrounding the human brain, the second biggest of these is that some people are left brain dominant and others are right brain dominant.

What exactly does this mean? I was at a complete loss to explain this to people when they either make such claims or ask such questions, because being a science student at times shields you from myths by studying only the facts. Therefore, let's blow this myth which has been a big commercial advert for multiple brain training games and programmes.

Let's see what created this notion in the first place?

1. Left versus right handers: a fact that we all are familiar with.

Handedness is the easiest one to notice. There is a genetic reason as to why most people prefer their right hand over left to perform majority of motor tasks.
Just like a bilateral human body in which the right side is the mirror image of the left, a symmetry also exists in the brain. The brain is divided into the right and the left hemisphere. For motor control that causes muscle movement in the body, the right side of the body is controlled by the left hemisphere and vice versa. So, it is possible that taking analogy from handedness the notion came into existence that even in the brain one of the two hemispheres might be more dominant.

2. “Nous parlons avec l’hémisphère gauche!” 
(We speak with the left hemisphere!) 
Brain asymmetry exists just like asymmetry of different internal organs. For majority of people liver is on the right side of the body and heart slightly towards the left. Now similar to such an asymmetric placement of organs in the body, there is functional asymmetry between the two hemispheres of the brain. The discovery of Broca's area, which is present in the left hemisphere and is responsible for creating articulate speech and understanding language, provided localized regions for brain function. It was discovered when a patient came to Paul Broca, who could not speak anything else other than Tan. When this patient died, a specific region in the left hemisphere (which is now termed as the Broca area) was found to be damaged by a brain lesion. This provided early cues to how there could be sepatrate regions in the brain that govern specific functions. Thus, the discovery of Broca's area, a speech area in the left hemisphere of the brain must have started this myth.

3. The split brain 
Further research into the field of brain lateralization was carried out and it was Roger Sperry (who won the Nobel Prize in 1981) who while studying the role of corpus callosum, the connecting tether between the left and right hemisphere of the brain, made the discovery that added the most credibilty to this myth. He performed split brain experiments on animals and studied epilepsy patients who had their corpus callosum severed. He found that the two hemispheres act as independent brains with the communication between the two abrupted. Now, when these split brain people were shown a word with their right eye they could speak it but when shown with the left eye they could not. This led him to conclude that left brain hemisphere processes language.

Now that we know what started this myth let's see some facts that shall shatter it. So, left side of the brain controls language and logic, while right side controls creativity and imagination as per the popular myth.
The only truth in this is left side of the brain has centres that control language comprehension and helps in creating speech. It also has centers for understanding semantic information associated with language i.e., logic behind what is being said or is written. While the right brain has centers that help in assessing emotional aspects of lnaguage. Thus, you need  both the hemispheres to understand langauage.
When it comes to creativity, we still don't know how and what kind of genes can actually make a person more creative and brain scans show activity all over the brain when a person is engaged in a creative task.
Just like for digesting your food the entire gut along with organs placed on the right and left work together, to do a task as to write or make a picture, we require a whole lot of collaboration between different areas of the brain, now some are present on the left side while others on the right.

I discovered some cool blogs while writing this post. The first one features animated videos where you can know more such brain myths that are prevalent and the second one talks about Broca's work and how brain laterilazation was discovered with the interesting story of his patient who could not speak anything else but Tan.

You can also watch House MD, season 5, episode 24 (Both sides now) to make it more interesting!

Eric Kandel's Principles of Neural Science.

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