The human brain is divided by the sagittal slit into two halves which can be clearly differentiated and are called cerebral hemispheres.
These hemispheres are interconnected by bundles of neural fibers that belong to the corpus callosum, and although at first glance they both appear to be symmetrical hemispheres, the truth is they are not.
These differences between the two hemispheres give the name to the hemispherical specialization, and will be explained in more detail in the next section, but before that there will be a brief overview of what has been studied about hemispherical specialization, so you know what this discovery is all about.
What is hemispheric specialization?
What is called hemispherical specialization is the set anatomical and neurochemical differences, in addition to all the different functions performed by the left hemisphere compared to the right and vice versa. Hemispherical specialization is also known as the concept of lateralization.
Lateralization is made up of the functions and processes that are specific to each hemisphere, and therefore the abilities that are done primarily through a hemisphere would be said to be lateralized.
The hemispherical specialization or lateralization of certain functions of the brain is based on the idea that there are specific regions in the brain that are responsible for performing specialized actions.
Another relevant concept in the field of hemispheric specialization is laterality, which should not be confused with lateralization. Laterality is the predominance in the handling of the right limbs or, on the contrary, those on the left side of the body. For example, having a right laterality is what is colloquially called “being right-handed” or “being left-handed”, in the case of having a left laterality; have a majority of skilled people.
Differences between the two hemispheres of the brain
In this section, we will see some of the actions carried out laterally by each hemisphere, as well as those carried out by interhemispheric intervention.
1. Right hemisphere specialization
The right hemisphere is responsible for controlling and receiving sensations on the left side of the person’s body. According to the most accepted theories on hemispheric specialization, the right hemisphere is able to process the information that comes to it in a comprehensive and non-methodical way, with an emphasis on spatial and visual relationships. Therefore, the right hemisphere is considered to be the creative and intuitive part of the brain.
This hemisphere allows us to exercise skills such as having holistic or holistic thinking in our mind, which is based on having abstract ideas and also being able to globally see a set of elements that are related to each other (for example, when painting an image, we have the ability to imagine an image as a whole and then proceed to paint, step by step, each of the parts that compose it).
The right hemisphere too it allows us the ability to intuition, to pick up the non-verbal signals that are transmitted to us by another person, to visualize the emotions expressed by others, exercise our artistic and musical creativity and fantasize.
2. Left hemisphere specialization
The left hemisphere controls and perceives sensations in the right part of the body.
The left hemisphere performs information processing progressively, analytically and systematically. This hemisphere emphasizes episodic or temporal relationships. By these characteristics, we know that the left hemisphere makes up the analytical and rational part of the human brain.
The left hemisphere is the part of the brain that allows you to perform logical reasoning, solve mathematical problems and calculations, perform linear and sequential thoughts, thoughts through language, and remember the facts of life. past, as well as thinking about the future.
3. Interhemispheric integration
There is scientific research that has found that there are also actions that are made across both hemispheres. This is done through various communication channels that are found in the corpus callosum and allow their interconnection.. These types of operations, involving both hemispheres, are known as hemispherical integrations.
Interhemispheric integration comes into play when performing certain tasks, for which there must be this interaction between specialized regions that are found in both hemispheres of the brain.
We know that during the exercise of activities, generally attributed to a hemispheric specialization, it was possible to verify later that, even if it is less, the other hemisphere is also involved.
For example, when understanding a metaphor or a proverb, being tasks of linguistic reasoning, one knew that the left hemisphere was involved; however, it was later discovered that the right hemisphere is also involved.
The same goes for visuospatial skills (e.g. differentiating between left and right), which are typically associated with the right hemisphere, although the left hemisphere is also involved.
On the other hand, it has been found in research that some people with a serious injury in one of the hemispheres had some difficulty processing information. For example, patients who have suffered an injury to the right hemisphere have difficulty paying attention to the general shape of objects; while those with an injury to the left were unable to pay attention to the details of the objects, but could identify the full shape of the object.
So when we analyze an image, such as an artistic painting, we need the coordinated work of the two hemispheres. The right hemisphere would allow us to visualize the image represented in the painting in a comprehensive and harmonious way, while thanks to the left hemisphere we could appreciate the nuances of the image, such as the gestures of the characters represented, the clothes and many other details.
The following section will briefly explain how the current knowledge regarding hemispheric specialization was obtained.
Historical review of the discovery of hemispheric specialization
The specialization of each hemisphere was born as an idea around 1860, following the discovery of the French doctor Paul Broca, who discovered that the left hemisphere was essential for human beings to process language.
This happened while he was treating a patient with a left hemisphere injury and therefore had serious difficulty speaking, being able to say only the word “therefore”. Still, he was able to understand the language heard, proving that he could follow simple commands.
Later, after seeing several cases similar to the one reported above, he was able to observe that in all of them there was an injury to the lower prefrontal cortex of the left hemisphere, the area which became known after involving the production of speech. This is why it was baptized the district of Broca. So, a condition in this part of the brain is called Broca’s aphasia.
The discovery concerning the area of the brain that allows the production of speech was confirmed by Karl Wernicke, psychiatrist and neurologist of German origin, who also discovered another area located in the left hemisphere, more precisely in the temporary lobe which , being injured, prevented the patient from understanding the language, although he was able to articulate simple sentences. This area was later named the Wernicke area. When this area is injured, the patient’s condition is known as Wernicke’s aphasia.
English neurologist John Hughlings Jackson studied different phenomena in which one hemisphere dominated mental function over the other., calling these cases the cerebral dominance. Thus supporting the ideas of Broca and Wernicke, who had shown that the understanding and production of language rested on a dominance of the left hemisphere.
In the 1920’s, English neuropsychologist Brenda Milner found that injury to the temporal area of the right hemisphere resulted in the inability of those affected to assimilate new memories into memory., although cognitive abilities such as perception, language and reasoning fully functioned normality.
Roger Sperry did the research that was instrumental in adopting the theory of hemispheric specialization. His investigation began with a World War II veteran who had been shot in the head by a bomb explosion and, as a result, was continually suffering from epileptic seizures. Then the surgeons who operated on him decided to cut the corpus callosum from his brain and the epileptic seizures disappeared.
However, although he no longer suffers from epileptic seizures, he cannot be free from certain side effects. His right hemisphere is the one that emerged unscathed from the operation, and as a result, the patient was unable to control the limbs on his left side. Instead, he was able to control his right limbs and was also able to understand language, since this function is handled by the left hemisphere.
It was from Sperry’s discovery that more emphasis was placed on the hypothesis which deduced that each hemisphere and each of the domains are specialized in concrete functions, without neglecting the interhemispheric integration functions. It was then that the exhaustive work, which continues to this day, began to investigate the functions of areas and hemispheres of the brain, one of the most important unknowns in the study of humans.
- Andreu, L. (2017). Hemispheric specialization. In Redolar, D. (Coord.) Cognitive Neuroscience (pp. 463-484). Madrid: Editorial Médica Panamericana.
- Machado, S. et al. (2013). Hemispheric specialization and regulation of motor behavior from the point of view of cognitive neuroscience. Mental Health, 36, 513-520.