Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!

Who's to decide which side?

LuisanaT's picture
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.
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (13) (14) (15) (16)