I am left-handed, what about you?

A matter of hand

Around 90% of the population use their right hand to write, 9% are left-handed and 1% is ambidextrous. Lefties earn on average 10% lower wages, and are dominant in creative and artistic carriers. How is that possible? Why are some people right-handed, others left-handed and a couple are both? What are the implications of such a random process and what are the outcomes?

Answers to these questions lie in the brain of course, buried deep inside its structure. In this article, I will talk about our brain hemispheres, and differences stemming from the involuntary choice of being a left or a right-handed. It does not only play a role in what hand will be used to write, but sheds light on some deep and complex brain wiring even affecting how our thoughts are processed. The first part of this article will be mostly about biological and physiological phenomenon related to handedness, while the second part will concern life outcomes of handedness.

The first thing to know is that our brain is separated in two different hemispheres: the left and the right hemisphere. It is simply a denomination used to separate in two sides our brain. This does not contradict the brain’s fundamental structure – reptilian brain, limbic brain and Neocortex – our hemispheres contain these structures. Linked together through the corpus callosum – a high amount of nerve fibres – our hemispheres are constantly communicating with each other.

On their surface lies the grey matter, also called the cerebral cortex. It has a role in consciousness, language, memory, attention, thought and perceptual awareness. An inner white layer supports the cerebral cortex, and is therefore called the white matter. While the grey matter contains neural cells, the white matter doesn’t and has cells used to transmit signals from regions to others.  Its white colour comes from the amount of formaldehyde, an organic molecule used to preserve the white matter.

The second thing to know is that each hemisphere controls one part of our body. This phenomenon is called lateralization; it means that the brain is a paired organ, composed of two halves. While they look identical, they are in fact complementary. Both are deeply related to each other, and their functions depend on one simple thing: are you a left or a right-handed? This question is crucial in the functioning of our hemispheres: one hemisphere is dominating the other. A right-handed will have his left hemisphere dominating his right body side; the other way around applies if you are a left-handed.

In that way, sensory information is sent accordingly to the opposite hemisphere responsible for it: for example, sensory inputs on the right side of the body are sent to the left hemisphere, same applies with the left side of the body. This explains why damages to one side of the brain lead to fewer responses from the opposite side of the body.

Lateralization occurs differently with language, speech or spatial abilities than it does with sensory inputs. Hemispheric specialization appears to take place for these abilities regardless of handedness. 95 % of right-handed uses their left hemisphere for language abilities, however it happens that 60 to 70% of left-handed uses their left hemisphere as well for the same function while 30% of them use their right hemisphere. Lateralization occurs here, each hemisphere has its specific abilities. Look at the picture below to obtain a fully understanding of abilities differences:Image

Questions might arise regarding lateralization of special brain functions: if our brain is a paired organ, why are language and other abilities concentrated in one hemisphere? There are some hypotheses for this hemispheric specialization, and one for this comes from evolutionary scientists. As language and spatial abilities require fast information treatment, having them located in only one hemisphere allows faster processes. Inter-hemispheric communication and treatment take more time and can slow down other process.

While answers exist regarding the implication of being a left or right-handed and roles of the two hemispheres, the main question remains: why are some people left-handed and other right-handed? Unfortunately, there are no proven answers to this question yet. Scientists agree that it is the result of both biological and environmental factors. Depending on your parent’s handedness, you might inherit their sidedness. But environment is a key factor and in lot of cases, children will end up with different handedness than their parents.

However, a recent theory sheds light on handedness as a result of stress level during pregnancy. This theory demonstrates that one molecule, the cortisol, might act on the fetus development if the mother experiences high level of stress while pregnant. The Cortisol is our body stress molecule. Produced when we feel stressed, it  can pass through the placenta barrier and interfere with the fetus. The more is produced, the larger the affect it will be important on the fetus’ brain development and will lead to different brain wiring. Mothers who felt really stressed during their pregnancy are therefore more likely to give birth to left-handed or mixed-handed child.

As more and more are discovered about the origin of handedness, scientists and economists observe the effect of such a process in real life. What are their observations? What are their conclusions? As stated at the beginning of this article, left-handed people earn in average 10% lower wages. A higher proportion of left-handed can be found in artistic and creative carriers. Of course, this doesn’t mean that most lefties will have careers in creative and artsy areas, but their proportion is much higher in these careers than in any other area (for instance in business). This result is related to the fact that left-handed people are better in divergent thinking, which is simply thinking in creative ways. Because their brain is wired differently than right-handed, it allows them to process language, spatial relations and emotions in more diverse and potentially creative ways.

Having a brain wired in such a way isn’t only positive: studies have shown that there is a higher schizophrenia, ADHD (Attention Deficit Hyperactivity Disorder) and mental disorders rate among the left-handed population. Around 20% of people suffering from schizophrenia are lefties. Scientists believe it is related to brain lateralization as diverse brain pathways can lead to less effective communication between hemispheres and may be more prone to impaired learning or functioning.

To conclude, I would say it is quite interesting how a random and involuntary choice can have outcomes on our life, influences our future and can lead to both positive and negative results. Right-handed people are dominant, but lefties have been proven to be more successful in music, art or mathematics on a large scale. However, danger of mental illness is also higher.

Fun fact, 6 of the last 12 US presidents are lefties. Soon to rule the world?

More to read about handedness: http://brain.oxfordjournals.org/content/123/12/2512.full.pdf+html


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