Dominance, handedness and lateralization in terms of individuality

I have been thinking about the implications of my leftieness on the world. I started with the desire to better understand dominance in the human body and the factors influencing it. I had to re-define my concepts of handedness and explored brain lateralization. The factors influencing these complex issues eventually lead me to understand better the connections of specific parts of the body and how they work to create human individuality. I want to discuss the different summaries of observations on handedness that I found and explain the complexities behind them. I will also mention the implications of my findings to me personally and to educations as well as personality in general.

The starting point of this paper is to define handedness. Some people think of handedness as being divided into specific categories: left, right or ambidextrous (1). My personal belief is that handedness should be measured in degrees; it should be seen as a continuum instead of being divided into separate categories.  The reason behind this belief is that when my mother was small she was left-handed but since she was not allowed use her left-hand she switched to her-right. When I was small the same thing happened to me but I was never able to change my handedness. My explanation: I was a bigger lefty than my mother, and thus various degrees of hand dominance must exist. Online there are many theories about handedness as a continuous change for example by M.K. Holder (1,10).

 

Dominance is a complicated topic to approach. Some people see it as the ‘superiority’ of one side of the body over the other, while to others it is a ‘preferred’ side. People exhibit different forms of dominance such as handedness, footedness, earedness, eyedness etc. The origin of dominance and the reason for its existence are interesting topics to explore, but not always easy to approach. In the book ‘the Dream drugstore’ chapter four discusses handedness, stating that: “There are no absolute answers to questions about left-handers; the reply must always begin with, ‘it depends on who you call left-handed’” (1,5). I agree with this statement and we will see in the rest of this paper that this description accurately describes the problems concerning handedness as well as hemispheric dominance.

     

Hemispheric dominance or brain dominance is an important form of dominance since the two hemispheres actually differ in structure and function. Research done by Broca and Wernicke resulted in the identification of the language centers in the brain that were only present in one hemisphere. Broca and Wernicke both worked with patients who suffered from different forms of aphasia’s (the inability to understand language, process language or form coherent sentences) (3). Using this information they were able to identify specific structures in the brain responsible for language (3). The same was done for the non-verbal or visual parts of the brain.  Since the brain is asymmetrical the question of dominance is also a question of the nature of processing that is preferred in the brain (4, 7). The specialization of specific functions in one half of the brain is called brain lateralization. The specialization of these specific parts of the brain is thought to make it more efficient and save space as well as resources (12).

     

The link between handedness and hemispheric dominance is based on the simple logic that one’s preferred hand must mean that the hemisphere controlling this hand is also preferred. This means that right-side of the brain is dominant in left-handers while the left-side of the brain is dominant in right-handers, since the brain works contra-laterally (meaning that the left-side of the brain is responsible for the right-side of the body and reversed) (2, 7). In most people the verbal processing (assumed to be more linear and sequential) is located on the left-side of the brain, and the non-verbal processing (thought to be more holistic and random) on the right-side of the brain (11). As we saw before the definition of handedness is not that simple, there are varying degrees of handedness, and the same is true for the lateralization of the brain. Furthermore, not everyone has this traditional organization of the brain, a small percentage of people have a reversed organization of the structures in their respective hemispheres (from this small percentage the majority is left-handed)(7).

     

Although the general structure of the brain might be similar in most individuals, this does not mean that left-handedness will result in right-side dominance of the brain. There are many factors and varying degrees of lateralization involved in determining hemispheric dominance as well as handedness. Handedness for example, is influenced by genetics (9), learning and chance (hormone levels and conditions during pregnancy are also thought to have an influence) (5,8). The factors determining hemispheric dominance could be similar to those determining handedness but this does not always have to be the case. Similarly, it is hard to isolate one single factor and see if it is truly important in determining dominance or not. We can therefore say that it is better to use The Wada test or brain scans over handedness as an indicator of hemispheric dominance (6).

     

We have seen that it is incorrect to assume a correlation between hemispheric dominance and handedness. Other theories, based on this connection, discuss the importance of preference of the brain because of the way information is processed. I was always told that I was more creative because I’m left-handed. What was implied here was that left-handedness was equal to having a preference in visual-processing, on the right-side of the brain, over the verbal-processing of the left-side. The right-brain thinkers (and often implied left-handers) were considered to be more holistic thinkers that would not function as well in the linear world created for the majority of left-brained thinkers. What these theories leave out however, is that there can be many other reasons explaining the presence or lack of creativity and relative success within an individual.

     

In reality I’m not creative at all. In the online ‘hemispheric dominance tests’ the results always show me that my left-side is more dominant (these tests should not be taken to serious but are still interesting) (13, 14). Besides the fact that I might have a different organization of the brain that could explain my lack of creativity, it is also important to keep in mind that handedness has not been proven to have much (if any) influence on one’s personality. To make the confusion complete we don’t know the exact nature of the connection between handedness and hemispheric dominance. It is also important to keep in mind that the coordination and cooperation between the different parts of the brain is just as important, if not more important, as their differences. Many parts of the body are controlled bilaterally (by both halves of the brain), and the cooperation through the corpus callosum is essential.

     

The influences of handedness as well as hemispheric dominance thus seem to reach much further than just a simple preference. Dominance has an effect on your individuality, not only as being part of the majority or minority in terms of handedness, but also due to the individual differences in forms of processing. The preference of visual over language or language over visual processing within individuals is important since it influences many aspects for example education. People have different needs and preferences when it comes to learning and absorbing information which should be included in teaching methods. Here we see how neurobiology is important in understanding and improving real world issues such as our educational system.

     

I have learned a lot about handedness, brain lateralization as well as the theories that are currently available on this topic. I still have many questions regarding dominance and the origins behind brain lateralization. This paper has made me think a lot about the brain and human individuality. In neurobiology we discussed a lot about how boxes within boxes and how they create our actions as well as our thinking. I realized that human individuality is created through complex systems and subtle, but important differences within people. The understanding of the brain is an important aspect in order to further understanding the uniqueness of individuals. I hope that my explorations of handedness and lateralization help other people explore their own personality, ways of thinking and discover their individual talents.    

References:

 

1. Holder, M.K. “What does Handedness have to do with Brain Lateralization (and who cares?)”. Primate Brain. Handedness and lateralization research. 2005. University of Indiana. 19 February 2009. < http://www.indiana.edu/~primate/brain.html>.

2. Holder, M.K. “Abstract of the Thesis”. Primate Brain. Handedness and lateralization research. 2005. University of Indiana. 19 February 2009. http://www.indiana.edu/~primate/92mphil.html.

3. Lee, Bora. “ The biological foundations of language”. Exploring the mind. Fall 1997. Duke. 19 February 2009. http://www.duke.edu/~pk10/language/neuro.htm.

4. Morris, Rich. “ Left Brain, right brain, whole brain?”. Geometry and the imagination. 2007. 19 February 2009. http://www.singsurf.org/brain/rightbrain.php.

5. Hobson, Allan. “The Nature and determinants of handedness”. The Dream Drugstore. MIT Press CogNet. 19 February 2009. http://cognet.mit.edu/library/books/mitpress/0262083094/cache/chap4.pdf;jsessionid=C8B07BBB7312E450AF6EE1B9DAE5BE95.

6. Buchtel, Henrey. “The Wada test”. 16 February 2004. 19 February 2009. http://www-personal.umich.edu/~gusb/wadadesc.html.

7. Bobby-Evans, Marion. “ Right brain/left brain: what is it all about?”. About.com: painting. 19 February 2009. http://painting.about.com/od/rightleftbrain/a/Right_Brain.htm.

8. Dittmar, Manuela. “ Functional and postural lateral preferences in humans: interrelations and life-span age differences”. Project muse. The Wayne state university press 2002. 19 February 2009. http://muse.jhu.edu/journals/human_biology/v074/74.4dittmar.html.

9. Annett, Marian. “Family handedness in three generations predicted by the right shift theory”. Annals of human genetics, Volume 42, issue 4. 28 September 2007. Interscience. 19 February 2009. http://www3.interscience.wiley.com/cgi-bin/fulltext/120055420/PDFSTART?CRETRY=1&SRETRY=0.

10.  Coren, Stanley and Porac, Clare. “Family patterns in four dimensions of lateral preference”. Behavior Genetics. 24 April 1980. 19 February 2009. http://www.springerlink.com/content/p14g1u14q2287557/fulltext.pdf.

11. “ Left vs. Right Which side are you on?”. 2005. Inteleggen Inc. 19 February 2009. http://www.web-us.com/brain/LRBrain.html.

12. Harvey, James. “Brain Lateralization”. Bravenet. 19 February 2009. http://www.theorderoftime.com/politics/cemetery/stout/h/brain-la.htm.

13. “ Hemispheric dominance inventory test”. Intelegen Inc.2005. 19 February 2009. http://www.web-us.com/brain/braindominance.htm.

14. “Brain dominance test (online test)” International PcE Network. Eterna. 19 February 2009. http://www.ipn.at/ipn.asp?BHX.