Left Vs Right

Each one of us at times is puzzled why he/she is unable to take decisions more precisely the quick ones, is well explained by the asymmetric behaviour of the cerebral hemispheres. One may posses more analytic and logical approach while the other may have more of a creative approach remains a mystery more so when it is depicted amongst siblings. All this is controlled by the cerebral hemispheres of individual human beings.

The human brain as seen from above resembles the halves of a walnut – two similar appearing, convoluted, round halves connected at the centre (fig. 1.). The two halves are called the “Left hemisphere” and the “Right Hemisphere”. The human nervous system is connected to the brain in a crossed-over fashion. The left hemisphere controls the right side of the body and vice-versa. If a person suffers a stroke or accidental brain damage to the half of his/her brain then the right side of the body will be most seriously affected and vice-versa.

LEFT AND RIGHT HEMISPHERE

Fig.1

In the brain of animals, the cerebral hemispheres are essentially alike, or symmetrical, in function. Human cerebral hemispheres, however, develop asymmetrically in terms of function. The most noticeable outward effect of the asymmetry of the human brain is handedness. For the past one-hundred and fifty years or so, scientist have known that the function of language and language related capabilities is mainly located in the left hemispheres of the majority of individuals approximately in 98% of right handers and in about two-third of left handers. Knowledge that the left half of the brain is specialized for language function was largely derived from observations of the effects of brain injuries. For e.g. an injury to the left side of the brain was more likely to cause a loss of speech capability than an injury of equal severity the right side. Because speech and language are so closely linked to thinking, reasoning, and the higher mental functions that set human beings apart from the other creatures of the world, nineteenth century scientist named left hemisphere the dominant or major hemisphere; the right brain, the subordinate or the minor hemisphere. The general view, which prevailed until fairly recently, was that the right half of the brain was less advanced, less evolved than the left half – a mute twin with lower level of capabilities, directed and carried along by the verbal left hemisphere.

A long time focus of neuroscientific study has been on the functions of a thick nerve cable composed of millions of fibres that cross connected the two cerebral hemispheres. This nerve cable is called corpus callosum. Earlier the corpus callosum was thought to be an important structure. But the studies showed that the corpus callosum could be completely severed without observable significant effect. Through a series of animal studies during 1950, conducted mainly at the California Institute of Technology by Roger W. Sperry et al, Ronald Myers, Colwyn Trevarthen et al. it was established that the main function of the corpus callosum was to provide communication between the two hemispheres so as to allow transmission of memory and learning.

Then during the 1960s, extension of similar studies to human neurosurgical patients provided further information on the function of the corpus callosum and caused scientists to postulate a revised view of the relative capabilities of the halves of the human brain: that both hemispheres are involved in higher cognitive functioning, with each half of the brain specialized in complementary fashion for different modes of thinking, both highly complex.

The research was mainly carried out at Cal Tech by Sperry and his students Michael Gazzangia, Jerre Levy, Colwyn Trevarthen, Robert Nebes, and others. The investigation centered on a small group of individuals who came to be known as the commissurotomy, or “split-brain patients”.

The Cal Tech group subsequently worked with these patients in a series of ingenious and subtle tests that revealed the separated functions of the two hemispheres. The test provided surprising new evidence that each hemisphere in a sense, perceives its own reality. The verbal half of the brain -the left brain- dominates most of the time in individuals with intact brains as well as in the split- brain patients. Using ingenious procedures Cal Tech group tested and found evidence that the right, non-speaking half of the brain also experiences, responses with feelings, and processes information on its own.

In addition the scientists also examined the different ways in which the two hemispheres process information. Evidence accumulated showing that the mode of the left hemisphere is verbal and analytical, while that of right is non-verbal and global. According to Jerre Levy the mode of processing used by right brain is rapid, complex, whole-pattern, spatial and perceptual-processing that is not only different from but comparable in complexity to the left brains’ verbal analytic mode. Additionally, Levy found indications that the two modes of processing tend to interfere with each other preventing maximal performance.

Based on the evidence of the split-brain studies, the view came up gradually that the both the hemispheres use high level, cognitive modes which, though different, involve thinking, reasoning, and complex mental functioning.

As a result of these extraordinary finding over the past twenty-five years and more, we now know that despite our normal feeling that we are one person – a single being – our brains are double, each half with its own way of knowing, its own way of perceiving external reality. In a manner of speaking, each of us has two minds, two consciousness, mediated and integrated by the connecting cable of nerve fibres between the hemispheres.

Sometimes they cooperate with each other contributing its special abilities and taking on the particular part of the task that is suited to its mode of information processing. At the other times, the hemispheres can work singly, with one half “On”, the other half more or less “Off”. And it seems that the hemispheres may also conflict, one half attempting to do what the other half “knows” it can do better. Furthermore, it may be that each hemisphere has a way of keeping knowledge from the other hemisphere. It may be as the saying goes, that the right hand truly does not know what the left hand is doing.

A Comparison Of Left-Mode And Right-Mode Characteristics

L-mode	R-mode
Verbal: Using words to name, describe, define.	Non-verbal: Awareness of things, but minimal connection with words.
Analytic: Figuring things out step by step and part by part.	Synthetic: Putting things together to form wholes.
Symbolic: Using symbols to stand for e.g. ‘+’ stands for the process of addition.	Concrete: Relating to things as they are, at the present movement.
Abstract: Taking out a small bit of information and using it to represent the whole thing.	Analogic: Seeing likenesses between things, understanding metaphoric relationship.
Temporal: Keeping track with time, sequencing one thing after another.	Non-temporal: Without the sense of time.
Logical: Drawing conclusions based on logic: one thing following another in a logical order.	Intuitive: Making leaps of insight often based on incomplete patterns, hunches, feelings, or visual images.
Rational	Non-rational
Digital: Using numbers.	Spatial: Seeing where things are in relation to other things, and how parts go together to form a whole.
Linear: Thinking in terms of linked ideas, one thought directly following another, often leading to a convergent conclusion.	Holistic: Seeing whole things all at once; perceiving the overall patterns and structures, often leading to divergent conclusion.

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