Left Behind? The Deal with Handedness and What It Says About the Brain

Every now and then it is advisable to engage in a bit of house cleaning, venturing in all the nooks and crannies from the darkest depths of the basement to the harrowing heights of the attic. Preferring the latter’s airy condition to the eerie blackness of the former I decided to start by sorting through the clutter that was to be found in the hidden space above our heads.

In doing so I came upon an old guitar, previously owned by my grandmother’s late brother. Its body despite the years of use, and later seclusion, still exudes a nice golden glow and the sound of the instrument after a bit of tuning sounded wonderful. Soon after, my little cousins demanded they possess the instrument. My attempts to ward them off failed as their demands grew more rambunctious. To assuage their passions and protect the instrument from their angry plucking, I agreed to offer each one of them a simple beginner’s lesson. This calmed the brewing storm, but soon Kelly, the youngest of the bunch brought something to my attention: this guitar was made for right handed people and she was left handed. Another storm was brewing as she asked me if being left-handed meant she couldn’t play. I reassured her that there exist a variety of ways for left-handed people to play guitars, without forcing themselves to play right handed, such as playing upside down, switching strings, or buying a left-handed guitar.

Kelly seemed content with my answer and soon enough her attention span carried her off to discover new things, but the question still resounded in my head and made me think about the treatment of lefties in general.

From writing smudges and school desks to operating can-openers and other machinery, many operations or tools are built to suit right handed users only. Though it is true that over the last few decades, much more attention has been given to consumers with a stronger left hook than most, many providers of goods and services have not changed their routines or specifications by much if at all, and this is understandable seeing as only about 10% of the population are lefties. So in honor of International Lefties Day which was held this week on Tuesday, August 13, 2013, let’s take a closer look at lefties and handedness in general.

Why Left at All?

The human body, like that of many other organisms, is remarkably symmetrical. Its symmetry is present at the surface and below it. However, in some systems, like the brain, functioning is dramatically one-sided.

There are several theories floating around as to the origins of handedness and what drives its concretization, or lack thereof, in the brain. The big question about handedness though is why it is only present in humans. As of yet few workable hypotheses and even fewer counts of evidence attempt to provide an answer.

Regardless, handedness plays an important role in human life and our everyday interactions and behaviors. The brain’s asymmetry is such that critical intellectual cognitive skills like language and logical analysis are localized to the left hemisphere meanwhile creative, intuitive, and emotional faculties are localized to the right hemisphere. Also, counter intuitively, the right side of the body is controlled and largely connected to the left hemisphere while the converse is true for the left side of the body. This physiological arrangement lends some explanation to why left-handed individuals are more vulnerable to negative emotions including depression and anger. Lefties are more prone to fearful emotions than righties and thus more vulnerable to fear-related cognitive disorders or traumas such as post-traumatic stress disorder (PTSD) and certain phobias.

Given these rather negative possible effects of being “right-brain” dominant it would seem there is no evolutionary incentive for left-handedness. Still, a significant percentage of left-handers have a flipped language dominance in their brains meaning that their right hemisphere is home to greater language processing capacities than their left hemispheres. On top of that many left handed individuals have an “almost equal distribution of language skills in both hemispheres” according to Dr. Daniel Geschwind, professor of neurology, psychiatry and human genetics at the University of California, Los Angeles.

This is a prime example of the amazing property of neuroplasticity, the brain’s ability to reorganize itself dynamically to accommodate internal physiological or external environmental changes. According to Geschwind, “left-handers are less constrained when it comes to brain asymmetry, so their skills are most randomized and less specified” to a single hemisphere.

This translates into a huge advantage in terms of the robustness of the brain. Stroke patients or victims of serious head injuries usually have trouble recovering certain skills and readapting to using different parts of their brains to compensate for damaged or lost areas. Left-handed patients due to the wider distribution of specialized networks throughout both sides of the brain tend to recover faster than their right-handed counterparts.

Note, however, that “having more distributed language abilities probably makes the system more complicated, so it may increase the susceptibility to developmental [abnormalities] and neurodevelopmental disorders” says Geschwind, possibly explaining results of studies that found correlations between the risk of ADHD, autism, and dyslexia amongst left-handed people. An addendum to this note: study results provide averages and one should proceed with caution when making such generalizations any group of people.

In the case of left-handed individuals, there many external factors that one should consider when reviewing study results. Societal pressures to abandon left handedness at an early age certainly have an impact on early development and consequently the results of such studies. Furthermore, as I discussed before, the operational or everyday bias towards right handed people systematically places left-handed children at a sort of disadvantage compared to their right handed peers who do not have to readjust their behaviors to undertake certain tasks. This readjustment capacity is something that is unique, in degree, amongst children lending some support to the idea that the older you get the more you are stuck in your ways.

Asymmetry is for Grown ups

How exactly does the early brain configure handedness? Is it a property defined by the structure of the early brain or does handedness arise concurrently with the development of the brain, selected to contribute to a special organization that allows for a wider distribution of neural networks? Current evidence seems to support the latter with left-handedness pinned as a marker for a more symmetric organization of the brain.

I suggest we look to patients with isolated or missing hemispheres for answers. A hemispherectomy is a surgical procedure that involves the removal of an entire hemisphere of the brain to alleviate patients suffering from relentlessly malevolent seizures. This procedure is only undertaken in very young children because of the early brain’s lack of specialization and its high level of plasticity. I believe such patients hold very important clues that will help understand the need for widely distributed systems and why some brains select for them while most do not. Similarly we should look to patients who have undergone a commissurotomy, another epilepsy alleviating procedure where the corpus callosum is cut to prevent signals from one hemisphere from reaching the other (thus containing the epilepsy).

Not Left Behind…

In the end, lefties have much to be proud of. Left-handed players comprise a disproportionately large percentage of individuals who score well on assessments in school and have a high IQ. This also holds true for mathematicians and musicians – another reason why Kelly should not despair.

There are still many things to investigate with regards to handedness but for now lefties should just sit back and celebrate their differences. Everyone is entitled to their own idiosyncrasies and it is these very same differences that make each of us unique, allowing us to have different perspectives on life and contribute something interesting to society.

Also diversity gives us a better chance of surviving mass extinction.

Unless Godzilla.

— Patrice-Morgan Ongoly

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