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

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 would be 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 injuries in one or the other brings with it different symptoms.

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 brain hemisphere

As you surely already know, when looking at a brain we can differentiate between two sides called hemispheres, one 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. They both have a superficial cerebral cortex, white matter, and basal ganglia. 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 a lot in terms of their functions, so much so that an injury to 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 “presents problems of the right hemisphere.”

Some complex cognitive functions are unevenly distributed in the brain and, in some cases, they can only be found in one of the two hemispheres. In case of such a situation, we say that such hemisphere is dominant for such function, being the case of the left hemisphere for language, being more verbal and analytical, while the right 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, of which there is no doubt thanks to the fact that it is supported by clinical practice is that lesions in one or the other hemisphere brings with it various problems. In fact, not only the laterality of the lesion implies one type or another of symptoms, but also in which lobe it occurred. An injury to the left parietal lobe brings with it different problems than an injury to the left temporal lobe would.

In general, it is considered that the areas of the association cortices of the frontal, parietal and temporal lobes of the left hemisphere are responsible for the functions associated with the understanding 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 brain preponderance of each individual is established during the first years of life. It is usual that when we are still very small the functions of language are located in both hemispheres to a greater or lesser extent but that, after a few years, the left hemisphere is the one that ends up specializing in linguistic aspects.

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

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


Problems associated with lesions in the left hemisphere lobes

The left hemisphere is not homogeneous, presenting several lobes, each of which performs some specific functions. This means that receiving an injury in the left hemisphere does not always bring the same symptoms, since It is not the same that it occurs in the occipital lobe as in the temporal lobe, for example. Next we are going to see the problems associated with lesions in the left hemisphere lobes.

1. Frontal lobe

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

Lesions in this lobe can lead to a number of problems, including simple motor crises, 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 may occur characterized by problems in the expression of verbal fluency, without the understanding of language having been necessarily compromised.

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

2. Parietal lobe

The left parietal lobe fulfills 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 an injury occurs in this libulus it can lead to various problems related to sensation, such as sensory crises. There may be an alteration or a significant reduction in sensitivity on the contralateral side of the body, that is, the patient may notice that his right arm or leg does not feel very well. Besides this, problems such as distortion of the body scheme can occur:

  • Autotopagnosia: difficulty locating the parts of our body in space.
  • Digital agnosia: inability to identify the fingers of the hand itself.

Lesions in the left parietal lobe often involve loss of lower visual field. Added to this, patients with left parietal damage show severe difficulties in naming objects (anomia), inability to carry out mathematical operations (acalculia), alexia, and agrafia.

3. Temporal lobe

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

The left temporal bone is also involved in emotional aspects of behavior and 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 seizures of impassivity.
  • Automatisms: behaviors without purpose.
  • Olfactory, auditory and visual complex hallucinations.
  • Mood disorders.
  • Déjà vu: feeling of having previously lived an experience.

When Wernicke’s area is in this lobe, in case of an injury right there can result in aphasia of understanding, in which the patient may manifest having a fluent language, but lacking in meaning by not understanding very well what is being said. The patient will show serious language comprehension problems, but not necessarily production problems, 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 an injury in this region, pThe patient may have paroxysmal visual hallucinations in the form of lights or colors that are not really there (simple partial seizures).

You can also give the loss of contralateral visual field, causing the patient to have the sensation of having gone blind in the right eye and seeing only the left half of his visual field (contralateral homonymous hemianopia)

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

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