Hemisferios Cerebrales (Right and Left): Functions and Parts

The brain hemispheres Are well differentiated in the human brain; Each receives information and controls the part of the contralateral body, called hemicampo. That is, the Right cerebral hemisphere Controls the left hemisphere and the left hemisphere the right hemisphere.

Although at first glance both hemispheres may appear the same, they actually possess anatomical and functional characteristics that differentiate them.

There are numerous researches throughout the history of psychology that have studied these differences. The first studies were carried out comparing the behavior of people with divided brain, without connection between their hemispheres, and healthy participants.

As the technology advanced, more sophisticated tests including neuroimaging techniques such as functional magnetic resonance imaging (fMRI), Magnetoencephalography (MEG) or the Electroencephalography (EEG). One of the tests most used today is the Wada test.

In the following video you can see the description of the Wada test performed by a patient from his own experience.

Functional differences between the cerebral hemispheres

Numerous studies have been carried out throughout history to locate which brain area was responsible for each function. The first step to check where a function is located is usually to find out if it is present in both hemispheres or only one of them.

For this, studies are usually done with patients with divided brain, who suffer a disconnection between the hemispheres, in addition to neuroimaging techniques where it is verified which hemisphere is most active while performing a task.

In general terms, it has been found that the most basic functions, such as perception and attention, are usually carried out with the participation of practically the whole brain, even in patients with split brain.

While more complex processes such as thought or language, often involve greater hemispheric specialization.

Visuospatial Processing

Visuospatial processing is responsible for analyzing and understanding how the environment around us is based on the visual information we perceive.

In general, the results obtained in neuropsychological tests, such as the Cubes On the Wechsler Adult Intelligence Scale ( Wechsler Adult Intelligence Scale, WAIS) indicate that this processing is mainly performed in the right hemisphere (Berlucchi, Mangun, & Gazzaniga, 1997).

Although these results are widely accepted in the scientific community, it is true that they do not occur in all cases, since there are people who have found greater activation in the left hemisphere When performing this type of tasks.

Memory

The memory Is a fundamental capacity in human beings since, in addition to helping us to remember facts and information plays a crucial role in the adaptation to the environment and the anticipation and planning of actions.

In general terms, it has been found that the most relevant area for memory is the medial temporal lobe, specifically the hippocampus .

Visuospatial memory has been associated with the right hemisphere hippocampus and verbal memory with that of the left.

One of the most well-known studies in this respect is that of Maguire et al (2000) carried out with London taxi drivers. This study showed that taxi drivers with more years of experience had a greater right hippocampus than participants who did not engage in driving.

Emotion

The perception and production of emotions is one of the most studied processes in psychology, and seems to be shared in both humans and other advanced mammals such as primates.

To study the processing of emotions, images of faces representing emotions such as anger or fear and others with neutral expressions are often used.

As for the lateralization of the emotions, there are two hypotheses:

• The first hypothesis states that the right hemisphere is dominant in terms of recognition of emotional information. Although both hemispheres activate when perceiving emotions it seems that the right is more effective than the left, especially when recognizing emotions in familiar faces.
• The second hypothesis considers that the processing of emotion is done bilaterally, but each hemisphere is specialized in one type of information. The right hemisphere would be in charge of processing the negative emotions while the left would be in charge of the positive ones.

The second hypothesis has not been as strong as the first, since some studies have found no significant difference between the type of emotion and the hemisphere that processes it.

Language

Language is a capacity found only in humans, although it is true that other animals also use communication systems.

Possibly this ability is what has most helped humans to evolve, as it allows us to represent and express objects that are not present, abstract things like feelings or plan complex sequences of actions.

As is widely known, language is mainly associated with the left hemisphere, although the right hemisphere is also activated when some linguistic tasks are performed, it does so to a lesser extent.

The first studies that found a greater dominance of the left hemisphere versus the law in terms of language were those performed by Paul Broca Y Karl Wernicke . Specifically, they identified the region responsible for the production of language and the person responsible for its comprehension, respectively called Broca area Y Wernicke area .

From these studies have been made many others to specify which areas form the circuits that are activated when performing different linguistic functions, but in general, it is still considered that the dominant hemisphere for language in the right people and in the majority of people Left-handers is the left.

Reasoning

Reasoning is perhaps the most complex capacity of human beings. In order to make a decision, a reasoning is made based on both the current situation and past experiences.

If all the variables that influence this decision are not known, an inference is made, that is, it is acted on the basis of what is most likely to occur as a consequence of our actions.

Some studies have been carried out to verify if there is any dominant hemisphere in this capacity. They have found differences between the hemispheres depending on the type of reasoning.

When all variables are known and reasoning is of causal type, what variable influences another / s, the most efficient hemisphere is the right.

Whereas, if all variables are not known and an inference is to be made, the dominant hemisphere is the left hemisphere.

In summary, it could be said that the left hemisphere is specialized in a reasoning more complex than the right.

When it is not known with certainty which reasoning is adequate, the complex reasoning carried out by the left hemisphere usually precedes it. Although, on many occasions the correct answer is the simplest.

In one study it was found that humans actually use left hemisphere reasoning more, although we make more mistakes because of it.

In this study participants were presented with a series of slides with a circle in the middle, in 75% of cases a red circle appeared and in 25% a green circle appeared, the order of presentation of the circles was random.

Participants had to press a green button if they thought the next circle to appear would be green and red if they thought the next circle would be that color.

The results showed that although it was totally impossible for the participants to know in what order the circles would appear, they would still try to find a pattern by pressing the green button when they"predicted"that the next circle would be of this color.

Obviously this strategy is not the most successful because it takes time to think and many errors are commented, while if the participants had repeatedly pressed the red button would have made fewer errors and also have been faster.

Individual differences

The main functional differences between the hemispheres have already been explained, but these differences are not present equally in all individuals. Hemispheric specialization depends on factors such as manual dominance or gender.

Manual dominance

Most people are right-handed, that is, they use the right hand more for motor functions, while only 10% of the population is left-handed.

In the past, it was believed that in right-handed people the dominant hemisphere for language was the left hemisphere, while in left-handed the dominant hemisphere was the right hemisphere, but today it is known that this is not so.

In 95% of right-handers it happens in this way, whereas in only 5% of right-handers the dominant hemisphere for language is the right. In left-handed people the percentages are much more similar, in 70% of the cases the dominant hemisphere for the language is the left, 15% for the right and in the remaining 15% the hemispheres are activated equally, there is no dominance Hemispheric.

Therefore, it seems that hemispheric dominance is not the one that determines manual dominance. The most accepted hypothesis argues that this dominance is determined by genetic components, although these are not yet known.

Gender

It is often said that women have more developed right hemisphere than men, but this is just a popular belief. The fact is that studies to date have not found significant differences in the activation of the gender-dependent hemispheres.

What if they have been found are differences in the accomplishment of tasks that activate one hemisphere more than the other. The most studied abilities have been motor, visuo-spatial, mathematical, perceptive and verbal.

• Motor skills. In general it has been found that the masculine gender performs motor tasks, such as the launch and reception of objects, more efficiently than the female. It might be thought that this advantage is due to cultural differences between the genera rather than the brain structure from birth, but these differences can be observed from age 3, and even in other species such as chimpanzees. These abilities are controlled predominantly by the left hemisphere.
• Visuospatial skills. It is common to hear that men have better visuospatial skills than women, especially if it involves driving a car, but studies do not endorse that belief. Although men are better at tasks of visuospatial orientation, women have an advantage in visuospatial memory tasks. Therefore, in practice, no gender would have an advantage over the other. These abilities are controlled predominantly by the right hemisphere.
• Mathematical skills. Another widely held belief among the population is that males have higher math skills than females, but this is not true either. The masculine gender does better the tasks of mathematical reasoning and the feminine the ones of calculus. These abilities are controlled predominantly by the left hemisphere.
• Perceptual skills. Studies show that women are more sensitive to all perceptual stimuli except visual ones. That is, they detect stimuli that are imperceptible to the male gender, and they also do so more quickly. These abilities are controlled by both hemispheres.
• Verbal skills. Several studies have shown that women are better than men in terms of fluency and verbal memory. These abilities are controlled predominantly by the left hemisphere.

Although these results have been obtained in reliable scientific studies it is important to know that the differences between the genders are smaller than the individual differences. That is to say, if two people of the same gender were caught at random, it is more likely that there were more differences between them than between two groups of different genera.

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