What happens when the left hemisphere of the brain is injured?

A summary of the effects of injuries to the left hemisphere of the brain.

The brain has two hemispheres which have functions in which they specialize. It is said that the left hemisphere is in charge of the verbal and analytical, while the right hemisphere is more involved in the artistic.

Although there are many myths regarding the abilities of each of the hemispheres, it is a clinical reality that presenting lesions in one or the other brings with it different symptomatology.

What happens when the left hemisphere of the brain is injured? Let's find out the answer below.

The effects of injuries to the left cerebral hemisphere.

As you probably already know, when observing a brain we can differentiate between two sides called hemispheres.One is located on the left side and the other on the right side. They are separated by the longitudinal fissure, joined by the corpus callosum and, in appearance, are very similar. Both have a superficial cerebral cortex, white matter and basal nuclei. In turn, they are divided into four lobes: frontal, parietal, temporal and occipital.

But despite having a very similar appearance and structure, the truth is that they differ quite a lot in terms of their functions, so much so that a lesion on one side or the other of the brain implies very different symptoms. In fact, in the clinical practice of neuropsychologists, it is common to speak in terms such as "this patient is very left-hemisphere" or "he has right-hemisphere problems".

Some complex cognitive functions are unevenly distributed in the brain and, in some cases, are uniquely right hemispheric. and, in some cases, can only be located in one of the two hemispheres. In the case of such a situation, we say that this hemisphere is dominant for this function, being the case of the left hemisphere for language, being more verbal and analytical, while the right hemisphere is more oriented towards spatial perception and artistic aspects, such as music.

Although the idea that one side of the brain is more rational and the other is more imaginative has been considered a controversial idea, there is no doubt that lesions in one or the other hemisphere bring with them a variety of problems. In fact, it is not only the not only the laterality of the lesion implies one or another type of symptomatology, but also in which lobe it has occurred.. A lesion in the left parietal lobe causes different problems than a lesion in the left temporal lobe.

In general, it is considered that the association cortex areas of the frontal, parietal and temporal lobes of the left hemisphere are in charge of the functions associated with the comprehension and expression of language, which is why it is assumed that the left hemisphere is dominant for verbal aspects.

An interesting aspect to comment on is that the cerebral preponderance of each individual is established during the first years of life. It is common that when we are still very young the language functions are located in both hemispheres to a greater or lesser extent but that, after a few years, the left hemisphere is the dominant one, the left hemisphere is the one that ends up specializing in the linguistic aspects of language..

However, it is always possible that while we are still very young we may suffer a brain injury. As the brain at an early age is a highly plastic organ, an injury to the left hemisphere does not mean that the ability to speak will be lost, in fact, as the right hemisphere harbors certain linguistic functionality while still small, as long as it is healthy, it can compensate for the problems of the other hemisphere so that in this case the verbal dominance is on the right side.

Unfortunately, although human beings enjoy the gift of brain plasticity, it is not forever. As we develop, our brain loses this capacity, which means that the older we get, the less likely we are to recover from a brain injury. In adulthood, in the event of an injury to the left hemisphere, problems related to language, both written and oral, will manifest themselves..

Problems associated with lesions in the lobes of the left hemisphere.

The left hemisphere is not homogeneous, presenting several lobes, each of which performs some functions that are specific to it. This means that receiving a lesion in the left hemisphere does not always bring with it the same symptomatology, since it is not the same if it occurs in the left hemisphere as in the right hemisphere. it is not the same if it occurs in the occipital lobe as in the temporal lobe, to give an example.. Below we will see the problems associated with lesions in the lobes of the left hemisphere.

1. Frontal lobe

The frontal lobe is involved in aspects of motor control and programming, being the place where we can find Broca's area, involved in the production of language.. The left frontal lobe controls the expressive function of language and is also responsible for other higher cognitive functions such as short-, medium- and long-term behavioral planning.

Lesions in this lobe can lead to various problems, including simple motor seizures, facial hypotonia and contralateral hemiplegia. In addition, there may be alterations in social functioning and, if the lesion is in Broca's area, motor aphasia characterized by problems in the expression of verbal fluency, without necessarily compromising language comprehension.

Other problems caused by lesions in the left frontal lobe are problems in reading and writing, in the form of alexia (inability to read) and agraphia (inability to write).

2. Parietal lobe

The left parietal lobe performs functions related to the integration and processing of multimodal sensory information.. This brain area is involved in the conscious notion of body schema, orientation, posture and spatial skills.

When a lesion occurs in this limb it can lead to various problems related to sensation, such as sensory seizures. There may be a significant alteration or reduction of sensation on the contralateral side of the body, i.e. the patient may notice that he/she does not feel his/her right arm or leg very well. In addition to this problems such as distortion of the body schema may occur.:

• Autotopagnosia: difficulty in locating body parts in space.
• Digital agnosia: inability to identify the fingers of one's own hand.

Frequently, lesions in the left parietal lobe imply loss of the inferior visual field. Added to this, patients with left parietal damage show severe difficulties in naming objects (anomia), inability to perform mathematical operations (acalculia), alexia and agraphia.

3. Temporal lobe

The left temporal lobe houses auditory functions, mainly related to language comprehension, located in this brain region.In this brain region is located Wernicke's area, which specializes in understanding language.

The left temporal is also involved in emotional aspects of behavior and in the conscious appreciation of the sense of smell..

It has been seen that patients who suffer a unilateral lesion (only in one hemisphere) in the left temporal lobe manifest problems such as:

• Paroxysmal attacks of impassivity.
• Automatisms: purposeless behaviors.
• Olfactory, auditory and visual complex hallucinations.
• Mood disorders.
• Déjà vu: sensation of having previously lived an experience.

As Wernicke's area is located in this lobe, in case of a lesion in this lobe, it can result in aphasia of comprehension. can result in aphasia of comprehensionIn this case, the patient may manifest to have a fluent language, but lacking in meaning because he/she does not understand very well what is being said to him/her. The patient will show serious problems of language comprehension, but not necessarily of production, as long as Broca's area has not also been involved in the frontal lobe.

4. Occipital lobe

Finally, we will talk about the left occipital lobe, to which visual perception and interpretation is attributed. That is why, in the event of a lesion in this region, the left occipital lobe may be affected.he patient may suffer paroxysmal visual hallucinations in the form of lights or colors that are not really there (simple partial seizures). (simple partial seizures).

There may also be loss of the contralateral loss of the contralateral visual fieldThis may cause the patient to have the sensation of being blind in the right eye and only seeing the left half of his visual field (contralateral homonymous hemianopsia).

As we have seen, each lobe of the left hemisphere brings with it certain problems. However, since it is uncommon for patients to suffer from brain lesions located in a single lobe or hemisphere, the symptoms associated with the lesions can be much greater, combined and aggravated in the particular case.