Psychology

Popular psychology often refers to people as left-brained or right-brained with a clear difference in cognitive style. Research in the area of neuroscience shows that in most people, one hemisphere of the brain is indeed dominant over the other. However studies of the brainwave activity of people who can be labeled right-brained or left-brained according to popular understanding do not reveal unequivocal differences in brain activity. However researchers have indeed found some interesting correlations between brain activity and cognitive style. A broad look at the various studies of neuroscientists that deal with differences in function between the right and the left hemispheres of the brain and the differences in brainwave activity between those who have a right-brained cognitive style and those who have a left-brained cognitive style, suggests that there is indeed some truth to the popular myth of the right-brained and left-brained individual. However it is obvious that the human brain is much more complex than pop-psychology makes it out to be.

In 1962 the two American treated a man experiencing worsening and drug resistant epileptic seizures with an experimental procedure they severed the nerve connections between the two hemispheres of his brain, splitting it into two (Gazzaniga, 2005).. The operation cured the man of epileptic seizures and left him with not one but two functional brains. The splitting of the brain allowed researchers to conduct various experiments to find out more about the brain, specifically to find out what computational tasks were delegated to which hemisphere of the brain (Gazzaniga, 2005).

The splitting of the brain did not cause anything like a dramatic change in a persons personality that had been noticed in other brain surgeries such as frontal lobotomies, instead the changes in brain performance were subtle and only visible through clever tests of cognition (Gazzaniga, 2005) . It was known that the left eye and ear are connected to the right hemisphere of the brain and the right eye and ear to the left hemisphere of the brain. When a person with a split brain was presented with information only to the right hemisphere of the brain, they were unable to verbalize it (Devinsky and Laff, 2003). Early studies of hemispheric functions reported that there was a clear cut functional difference between the two hemispheres of the brain, the left brain was where the language and logical ability of the brain resided, while the right brain had a more gestalt function it dealt with emotions, image processing, spatial relations, and holistic ideas. The specialized functioning of the two halves of the brain was dubbed brain lateralization (Devinsky and Laff, 2003 Gazzaniga, 2005).

Research indicated that for nearly everyone, one hemisphere of the brain is dominant, though some people appear to use both hemispheres of the brain equally (Ornstein 1997). The dominance of one hemisphere of the brain was termed cerebral dominance or hemisphericity or hemispheric laterality of the brain, in popular culture it became common to describe people as left-brained or right-brained. It was posited that over 95 of the population was left-brained, people who were organized, verbal and logic oriented whereas a 5 minority were the quiet creative geniuses whose minds were geared for imagination, abstract ideas and artistic endeavors (Ornstein 1997).

Neuroscience has now advanced beyond the early simplistic models of brain hemisphericity (Gazzaniga, 2005). Oversimplifying the issue of laterality, the early researchers placed entire facets of a brains function into one hemisphere or the other. Later researchers have found that the processes of a normal brain do not involve merely one hemisphere. Attempts to directly monitor brainwave activity in normal humans in order to determine cerebral dominance reveal that the brains processes involve extremely complex and fast interactions between the different sections of the brain which outstrip by far the reaction time within which it is possible to take data samples (Millar  Whitaker, 1983).

However it may be possible to generally say that a particular process is left or right hemisphere dominant or that it involves integrated functioning or complex interactions of both hemispheres of the brain (Levy, 1985). Modern day researchers are more wary of assigning specific roles to different hemispheres of the brain (Gazzaniga, 2005). For example, instead of saying that the left hemisphere handles detail and the right hemisphere handles holistic function, modern researchers are more likely to say that the left hemisphere of the brain is more suitable for handling specific details while the right hemisphere of the brain is more suited for examination of things from a holistic perspective (Ornstein 1997). In the field of language and learning, the left hemisphere of the brain is more suited for handling sentence syntax and literal meaning, reading and mathematical in most people is better at handling syntax and meaning, a more literal translation, and in reading and mathematical processing (Gazzaniga, 2005). The right hemisphere is better at contextual perception for example, in interpreting art and recognizing faces. For nearly 90 of humans, reception and transmission of speech takes place mainly through the left hemisphere of the brain (i.e., Brocas and Wernickes areas of the brain). In left handed people, who form 5-10 of a given human population, that figure is reduced somewhat, to around 60 (Ornstein 1997).

Measuring the hemispheric laterality is contentious subject amongst research scientists. Researchers have come up with many different ways to measure the hemispheric laterality of a persons brain (Russo, Parsegani, Papeschi, Nicolini and Trimarchi, 1985). The simplest and most commonly administered test of a persons hemispheric preference is, what is called the Preference Test (PT). Developed by Zenhausern in 1978, the PT is a series of questions, twenty in number whose answer is to be given on a scale of one to ten (Merckelbach, Muris, Horselenberg,  de Jong, 1997). Ten of the questions deal with stereotypical right-hemisphere processes and ten with left-hemisphere processes. The tests questions inquire about things that are difficult to objectively quantify, for example, here are some of the questions from Zenhausens Preference Test
Right-hemisphere items
How often does your thinking consist of mental pictures or images
How good are you at teaching andor explaining by manipulating objects
Left-hemisphere items
How often are your decisions based on objective facts rather than feelings
Do you use a serious, all business approach to solving problems (Russo, Parsegani, Papeschi, Nicolini and Trimarchi, 1985)

An obvious problem with the PT test is that starts off with the assumption that the theory of strict brain lateralization is correct and a preference for the left or right hemisphere items on the list will correspond with the actual preference in the brain for one hemisphere over the other. A 1996 study that compared resting brainwave activity through Electroencephalography, or EEG, with PT scores found a modest correlation between the two (Merckelbach, Muris, Horselenberg,  de Jong, 1997). It was found that a preference for Right Hemisphere items on the PT test corresponded modestly with the strength of alpha brainwaves in the mid-frontal lobe of the left-hemisphere of the brain in a resting state. Since alpha waves correspond to reduced activity in the brain, this suggests that the PT is a valid measure of hemisphericity in the brain of a person (Merckelbach, Muris, Horselenberg,  de Jong, 1997). However no significant correspondence was found between PT scores and the alpha power ratios in the parietal regions of the brain which can be interpreted as evidence against the validity of the PT (Merckelbach, Muris, Horselenberg,  de Jong, 1997).

The Merckelbach, Muris, Horselenberg,  de Jong study shows that there is indeed some truth to the right-brained and left-brained myth. However the exact extent of the difference and its implications for fields such as customized learning programs is yet to be determined.