The Myth of the Left and the Right Brain

We all know that we have two cerebral hemispheres, two large brain masses densely folded on its surface – the cerebral cortex – which is where the intellectual functions are located.


We all know that we have two cerebral hemispheres, two large brain masses densely folded on its surface – the cerebral cortex – which is where the intellectual functions are located. In the 1960s, the treatment of people with epilepsy refractory to drugs, used a new strategy: the callosotomy, cutting the corpus callosum, the white substance tape formed by between 200 and 250 million axons and connecting both hemispheres. The idea was to cut the connection to prevent the epileptic attack jumping from one hemisphere to the other and affect both. The surprising result was that both hemispheres were still functioning normally, the patient did not show two personalities or any dramatic signs of his divided brain and it was said, sarcastically, that the corpus callosum for the only thing that served was to transmit the attacks epileptics from one hemisphere to the other.


Although not everyone expresses it in the same way, according to this myth, students who are more intuitive would dominate the right hemisphere while those who learn sequentially, linearly, would be “brain-left”, that is, they would predominate the left hemisphere It is also said that in the people dominated by the left hemisphere logic prevails, rational and orderly thinking, while in the most creative and easily for art, dominate the right hemisphere. According to this way of thinking, the left hemisphere would focus on the details, on knowledge, on the perception of patterns, on strategies in practical things, it would be the place of mathematics and science, and it would act on insurance. The law, on the other hand, would be fixed in the great panoramas, in the present and the future, in beliefs and fantasy, it would be impetuous and take risks and would be the place of philosophy and religion.

The idea that there are people with left brains and others with a right brain is a widespread myth, even among well-educated people. A study conducted in Great Britain and the Netherlands, with a sample of 242 primary and secondary school teachers found that 91% of the British and 86% of the Dutch considered that there were differences in hemispheric dominance. That could explain the individual differences in each student’s learning.

Some educational programs encourage teachers to determine which hemisphere dominates in each child before starting to teach them anything. Once again a waste of time and resources, in a fiction without a scientific basis. The myth has derived as that the two hemispheres do not communicate well, that without a complementary aid at a reasonable price the subjacent hemisphere will not develop well and that we would be losing half of our brain potential. Myths always arise because they seem to explain something that we perceive, that each student learns in a different way, that there are different personalities and tastes for different things, that there are more systematic and other more imaginative people, but the myth of the left brain and the right brain it is not a good basis for explaining those individual differences.

The myth of the left brain and the right brain is also associated with other myths such as the sexual differences between the brains of men and women. The website of the Christian Working Woman, a Christian movement that encourages women to become ambassadors of Jesus Christ in their workplace, claimed that “men are typically very left-brain” adding with that imprudence that stupidity gives ” Women tend to be more of the right brain, but they have a bridge between the left brain and the right brain that men do not have ». Our brains are enormously similar, whatever the macho and Christian working women say. As Christian Jarret points out in his book Great Myths of the Brain, the thinking style of a hemisphere is sometimes attributed not only to particular types of people but even to languages ​​or religions.

In the spring of 2012, the chief British rabbi, Lord Jonathan Sacks, said in an interview on BBC Radio 4:

“What has made Europe so creative is that Christianity was a religion of the right brain translated into a language of the left brain, because all the primitive Christian texts are in Greek.”


The scientific basis of the myth is well known. The location of specific functions is something that has been known since the 1860s thanks to the work of Paul Broca. Broca presented the case of a patient, Louis Leborgne, who after losing his left hemisphere had lost the ability to speak. Another researcher, Wernicke also found that the understanding of language was in the left hemisphere and then researchers began to wonder what the law was doing. The neurologist John Hughlings Jackson proposed that the right side was that of perception while the French neurologist Jules Bernard Luis said that the emotions were located in the right hemisphere, much more primitive, while the intellect was in the left hemisphere, which was the civilized. Roger Sperry, who studied animals and people with divided brains and won the Nobel Prize, told the New York Times, “I am of two minds. In fact, just like you. And until recently, the America of the companies did not do much to take advantage of one of them. But now that we are up to the hilt in what is called the Creative Economy and the Conceptual Age no one can afford to ignore the inner artist: the right hemisphere of the brain ». Soon the usual magos and con artists emerged, selling treatments such as placing discs of metals and magnets on the surface of the body, “metal therapy,” which in theory-but never in reality-corrected mental or behavioral dysfunctions by balancing both hemispheres.

There are brain functions that are clearly lateralized such as language or visuospatial processing. In most right-handed individuals, paying attention to stimuli related to language generates brain activity mainly in the left hemisphere while paying attention to stimuli involved in visuospatial processing generates activity lateralized to the right hemisphere. You also see something similar with mathematics. Some arithmetic tasks such as counting or reciting multiplication tables recruit more neurons in the left hemisphere than in the right hemisphere, while other aspects, such as estimating how many similar objects are in a drawing, recruit more in the right than in the left. But in reality, the students, all the people, we use both hemispheres. No one can say if a student dominates the left or right brain because it is not, the information flows between both hemispheres through the corpus callosum in frequent round trips, and the brain recruits more or less areas, even in the opposite hemisphere, according to the need for processing. A striking example are the chess players. When identifying pieces and their types of movement a beginner player uses ventral brain regions in the left hemisphere but a great master recruits similar zones in the right hemisphere, establishing a parallel processing for the enormous skill that he demonstrates in the game.

Neuroimaging techniques participate in this confusion. In general, for the non-specialist the only thing that is seen after a study with PET or functional magnetic resonance are areas with bright colors very localized in one or the other hemisphere. It can lead to the erroneous image that they are isolated functional zones, islands of nervous activity. In fact, in the face of almost any task, large parts of the brain show activity. To determine which are the most specific areas or with a change in their basal level of activity more apparent what is done is to subtract from the image of the brain performing that task, the image of the brain at rest and then establish, arbitrarily, threshold levels. That is, if an area has not doubled or tripled its activity we can decide not to represent it even though it was active. That’s why neuroimaging illustrations can give an unrealized, more segregated image between both hemispheres, and with fewer areas involved than what actually happens. As far as we know, any complex cognitive function sets in motion a network with multiple regions, distributed in both hemispheres and functioning in a coordinated manner. Actually, we could consider the brain as a neuronal symphony orchestra, where depending on the moments there may be areas or even individual neurons that have greater prominence, but there are no silent elements – the myth of 10% – nor can we say that a part of the orchestra dominates over another, the myth of hemispheric dominance.


The issue of hemispheric dominance has been analyzed in detail using functional magnetic resonance. Nielsen and his group analyzed the brains of 1011 people aged 7 to 29 looking for evidence of a predominance of one hemisphere versus the other. The study included a fine analysis of 7,266 encephalic regions and function lateralization was seen but was always local, never global. It means, that there were regions that were more active in one hemisphere than in the other, but in no case was there an activation of one of the hemispheres that dominated the other. With age there were small increases in lateralization and no differences in lateralization between both sexes.

One of the possible damages of this myth is that it can make some students, or their parents or teachers, believe that they can not devote themselves to some careers, to some vital projects because they do not have the right brain. There is nothing to support this criterion, our brain is surprisingly plastic and its ability to learn is its greatest virtue. Some companies spread this myth as Nintendo that has a game entitled “Left Brain Right Brain” and that in its promotional material encourages you to find out if “you are a” righty “or a” lefty “». student-success-homepage-photoThe myth has reached the world of Neuroeconomics where it is said that the success of a company is based on getting the employees of the left hemisphere and those of the right hemisphere to learn to speak the same language. Neil de Grassé Tyson the famous astronomer and science popularizer said “I’m brained.” Not right brained or left brained. I have a brain ». It is difficult to make a translation but what it says clearly is that it is not left brain or right brain, it has a brain. And that’s the way it is for everyone.


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