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

The brain has two hemispheres which have functions in which they specialize. The left hemisphere would be in charge of what is verbal and analytical, while the right would be more involved in the artistic aspect.

While there are many myths regarding the abilities of each of the hemispheres, it is a clinical reality that having injuries in either one involves different symptoms.

What happens when the left hemisphere of the brain is injured? We find the answer below.

    The effects of injuries to the left cerebral hemisphere

    As you probably already know, by observing a brain we can differentiate two sides called hemispheres, one located on the left side and one 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. At the same time, they are divided into four lobes: frontal, parietal, temporal and occipital.

    But despite being very similar in appearance and structure, the truth is that they differ greatly in terms of function, so much so that an injury to one side or the other of the brain results in very different symptoms. In fact, in the clinical practice of neuropsychologists it is common to speak in terms such as “this patient is very heavily in the left hemisphere” or “has problems in the right hemisphere”.

    Certain complex cognitive functions are irregularly distributed in the brain and in some cases, they are only visible in one of the two hemispheres. If this situation arises, 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 is more oriented towards spatial perception and artistic aspects. , like music.

    While the idea that one side of the brain is more rational and the other more imaginative has been viewed as a controversial idea, there is no doubt that it is supported by clinical practice that injuries in one or more other hemispheres involve various problems. In reality, not only the laterality of the lesion involves one type or another of symptoms, but also in which lobe it occurred. Injury to the left parietal lobe causes problems other than those that would result in injury to the left temporal lobe.

    In general, the areas of the associative cortices of the frontal, parietal and temporal lobes of the left hemisphere are considered responsible for the functions associated with the comprehension and expression of language, which is why it has been assumed that the hemisphere left is dominant. for the 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 common that when one is still very young the functions of language are located more or less in both hemispheres but that after a few years, the left hemisphere is the one that ends up specializing in linguistic aspects.

    However, it can always happen that, very young, we suffer from a brain injury. Because the brain is an extremely plastic organ at an early age, an injury to the left hemisphere does not mean that the ability to speak is lost, in fact, as the right hemisphere harbors certain linguistic characteristics while it is still small. , as long as it is healthy, it can compensate for the problems of the other hemisphere by making the right side verbal dominance in this case.

    Unfortunately, while humans appreciate the gift of brain plasticity, it isn’t forever. As we develop, our brains lose this ability, which means the older we are, the less likely we are to recover from a brain injury. In adulthood, in the event of an injury to the left hemisphere, language-related problems will manifest themselves, both written and spoken..

      Problems associated with injury to the lobes of the left hemisphere

      The left hemisphere is not homogeneous, presenting several lobes each fulfilling its own functions. This means that receiving an injury in the left hemisphere does not always lead to the same symptoms, because it is not the same as in the occipital lobe as in the temporal, to give an example. Below we will look at 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, this is where we find Broca’s area, involved in language production.. The left front controls the expressive function of language and is also responsible for other much higher cognitive functions such as short, medium and long term behavior planning.

      Injury to this lobe can lead to a variety of problems, including simple motor seizures, facial hypotonia, and contralateral hemiplegia. In addition, alterations in social functioning may occur and, in the event of injury to the Broca region, motor aphasia occurs characterized by problems in expressing verbal fluency, without the understanding of language necessarily having been compromised.

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

        2. Parietal lobe

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

        When an injury occurs in this libel, it can lead to various sensation-related issues, such as sensory seizures. There may be an alteration or significant reduction in sensitivity on the contralateral side of the body, i.e. the patient may notice that their right arm or leg is not feeling very well. What’s more, problems such as distortion of body pattern can occur:

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

        Injuries to the left parietal lobe often involve loss of lower visual field. In addition, patients with left parietal lesions have severe difficulty naming objects (anomie), inability to perform mathematical operations (acalculia), alexia and agraphia.

          3. Temporal lobe

          The left temporal lobe hosts auditory functions, mainly related to language comprehension, being located in this region of the brain the Wernicke area which specializes precisely in the understanding of language.

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

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

          • Paroxysmal attacks of impassibility.
          • Automatisms: aimless driving.
          • Complex olfactory, auditory and visual hallucinations.
          • Mood disorders.
          • Already seen: feeling of having already had an experience.

          Finding Wernicke’s area in that lobe, in case of injury right there this can lead to aphasia of comprehension, in which the patient may manifest having fluent language, but no sense in not fully understanding what is being said to him. The patient will have serious problems with speech comprehension, but not necessarily production, as long as the Broca area has not been involved in the frontal lobe as well.

            4. Occipital lobe

            Finally, we will talk about the left occipital lobe, to which visual perception and interpretation are assigned. It is why, in case of injury occurring in this area, pthe patient may experience paroxysmal visual hallucinations in the form of lights or colors that are not actually present. (simple partial seizures).

            You can also give the loss of the contralateral visual field, which makes the patient blind in the right eye and only sees the left half of the eye. his visual field (contralateral homal hemianopia)

            As we have seen, each lobe in the left hemisphere presents certain problems. However, since it is rare for patients to suffer from brain damage localized to a single lobe or to a single hemisphere, the symptoms associated with the lesions may be much larger, combined and worsen in the particular case.

              Bibliographical references

              • Crossman, AR and Neary, D. (2011). Neuroanatomy. Barcelona: Elsevier Masson.
              • Halpern ME, Güntürkün O, Hopkins WD, Rogers LJ (2005). “Lateralization of the vertebrate brain: taking advantage of model systems”. Journal of Neuroscience. 25 (45): 10351-10357.
              • Sheppard, SM and Hillis, AE (2018a). That’s right ! Understanding of language beyond the left hemisphere. Brain, 141 (12), 3280-3289.

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