Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!
Who's to decide which side?
In the neural system, each hemisphere of the brain corresponds to the
opposite side of the body with one side being dominate. This inborn
characteristic of the humans’ renders us lateralized because, for
example, the dominance of the right cerebral is responsible for left-
handedness and vice-versa. (1) A great majority of humans are
right-handed, 85-90% while the remaining percentage is left-handed. (5)
But why is there such an unequal distribution? This can be due in part by
both social and consumer influences because they help finalize the
handedness of a person. For the right-handed culture we live in has lead
to many more individuals converting from left-handedness to
right-handedness than to right-handedness to left. (16)
A different approach in explaining this observation is by looking into the
lateral sulcus. This is the part of the human brain, generally longer in
the left hemisphere, divides the parietal lobe, which controls the sensory
information as well as the manipulation of objects and the understanding
of numbers, (3) with the frontal lobe which controls the coordination and
execution of behaviors. (4) This common additional contact of the lateral
sulcus in the left hemisphere can give rise to it being dominant,
consequently rendering more right-handed individuals.
But while 95% of right-handers obtain their language functions in the left
hemisphere, only 18% of left-handers obtain their language function
lateralized in the right. (2) The brain hemisphere division of labor
theory supports this idea, for it promotes the efficiency of hand-eye
coordination that can only be achieved most effectively if both speaking
and handiwork tasks are located on the same hemisphere. (5) There has been
research done that reveals that certain parts of the brain that
participate in the processing of certain pieces of information have a
greater oxygen dependency as a result of an elevated blood flow. (1) The
left side of the brain, controlling the right side of the body, seems to
governor the qualities of being analytical, verbal, logical, and literal.
(6) Despite all of this though, there is reason to believe that this is
not the case and rather it is the synergy of a balance between the two
hemispheres that accounts for the maximum learning and thinking
experience. (7)
Some of the negative health risks associated with people that are
left-handed include but is not limited to allergic disorders,
particularly rhinitis, asthma, eczema, urticaria, (8) developmental
delays and irregularities, deficiencies in the immune system due to the
intrauterine hormonal environment, and immune system disorders. (9)
Another correlation affiliated with being left-handed is being more
susceptible to breast cancer. Based on a study, left-handed women were
two times more likely to develop breast cancer because of high levels of
hormones that help determine hand preference may simultaneously influence
breast tissue. (10) A slightly different relationship, as established by
Geschwind hypothesis, is that with left-handedness comes vulnerability to
the AIDS virus. (13)
Serious accidents are also generally associated with left-handed
individuals. A story to help account for this direct relationship has to
do with the disruption and damage a change in handedness can cause to the
individual very young. Some of the symptoms that result from this
flip-flopping consist of disturbances in the encoding, storage, and
recall information processes of memory, and difficulty in things such as
concentration, reading, spelling spatial disorientation, speech
impediments, and fine motor skills. These symptoms can progress into
feelings of inferiority, shyness, overcompensation, provocative behavior,
personality disturbances, and emotional problems that can last into
adulthood. (13)
This last health risk, birth stress related neuropathy and birth-related
complications that involve reduced oxygen levels (16) can also support the
imbalance seen in the handedness of the human populations. For a traumatic
experience such as this would feed well into the dual brain theory which
suggests that the brain, being separated into two hemispheres, senses and
reacts to the environment independently from one another where one half
would have to dominate over the other in order to prevent it from further
damage. (16) Studies have been shown where children who suffered from
oxygen deprivation during the perinatal period also fall victim to
injuries in the dominant side of the brain, causing them to vary between
hand preferences until they’ve become of school age.
If in fact the hemisphere that holds to be dominate requires, because of
the brain hemisphere division of the labor theory, a greater supply of
oxygen to accommodate for the more complicated tasks it administers, then
oxygen deficiency at any age can cause great confusion. Because based on
the dual brain theory, one side of the hemisphere will compensate for the
other, rehabilitating of this dominant hemisphere and therefore
reestablishing the dominant hemisphere and handedness in that individual.
This scarcity, occurring frequently enough, can lead to understandable
disorientation in a person even more so if these temporary traumas
alternate between the two hemispheres it affects.
References
(1) http://www.linkshaender-beratung.de/english/Ambidextrous.htm (2) http://en.wikipedia.org/wiki/Lateralization_of_brain_function (3) http://en.wikipedia.org/wiki/Parietal_lobe (4) http://en.wikipedia.org/wiki/Frontal_lobe (5) http://en.wikipedia.org/wiki/Right-handed#Why_is_the_population_right-hand_dominant.3F (6)http://en.wikipedia.org/wiki/Lateralization_of_brain_function#Pseudoscientific_exaggeration_of_the_research (7) http://www.web-us.com/brain/LRBrain.html (8) http://findarticles.com/p/articles/mi_m0902/is_n5_v23/ai_17705180 (9) http://jerrymondo.tripod.com/lgev/id6.html (10) http://www.medpagetoday.com/HematologyOncology/BreastCancer/tb/1810(1)
http://www.linkshaender-beratung.de/english/Ambidextrous.htm (13)http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&uid=2055043&cmd=showdetailview&indexed=google (14) http://en.wikipedia.org/wiki/Left-handed (15) http://www.linkshaender-beratung.de/english/Ambidextrous.htm (16) http://en.wikipedia.org/wiki/Dual_brain_theory
References
(1) http://www.linkshaender-beratung.de/english/Ambidextrous.htm (2) http://en.wikipedia.org/wiki/Lateralization_of_brain_function (3) http://en.wikipedia.org/wiki/Parietal_lobe (4) http://en.wikipedia.org/wiki/Frontal_lobe (5) http://en.wikipedia.org/wiki/Right-handed#Why_is_the_population_right-hand_dominant.3F (6)http://en.wikipedia.org/wiki/Lateralization_of_brain_function#Pseudoscientific_exaggeration_of_the_research (7) http://www.web-us.com/brain/LRBrain.html (8) http://findarticles.com/p/articles/mi_m0902/is_n5_v23/ai_17705180 (9) http://jerrymondo.tripod.com/lgev/id6.html (10) http://www.medpagetoday.com/HematologyOncology/BreastCancer/tb/1810(1)
http://www.linkshaender-beratung.de/english/Ambidextrous.htm (13)http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&uid=2055043&cmd=showdetailview&indexed=google (14) http://en.wikipedia.org/wiki/Left-handed (15) http://www.linkshaender-beratung.de/english/Ambidextrous.htm (16) http://en.wikipedia.org/wiki/Dual_brain_theory