This cerebral lobe is responsible, among other functions, for visual perception.
In this article we will talk about one of these lobes: the occipital lobe, responsible for the human visual system and perception. We will know its location, its functions and the clinical manifestations that cause the lesions in the different areas in which it is divided.
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Cerebral lobes: the occipital lobe
The human brain is highly complex. The functions in which it intervenes are strategically organized through its different structures. At the anatomical level, the brain is made up of four lobes, which are four parts or areas of the cerebral cortex.
Thus, each of the lobes is located in a different part of the brain, and is responsible for certain functions. Specifically, we talk about the following lobes: temporal,frontal, occipital and parietal. In addition, all lobes maintain connections between them.
In this article we will talk about a lobe, specifically, the occipital lobe, mainly related to a sensory system: the visual system, which also includes perceptual processes.
Location and structure
The occipital lobe is located at the back and bottom of the brain. Specifically, it is located behind two other lobes: the parietal and the temporal. As with all brain lobes, we find an occipital lobe in each cerebral hemisphere (the two halves into which the brain is divided).
This lobe covers between 10 and 14% of the total neocortex; The neocortex is the newest, largest and most developed part of the brain. At a structural level, the occipital lobe is connected to the primary visual cortex and the primary visual association cortex, areas related to vision, other sensory systems, and perception.
Functions
We will see in detail what the main functions of the occipital lobe are below.
1. Vision
The occipital lobe is primarily responsible for vision, that is, the visual system; that is, it enables vision . For the person to be able to see, however, it is also necessary that the visual organs are preserved (the optic nerve, the eyes…).
In this way, this lobe is responsible for processing visual information (visual stimuli) that appear in our environment. In addition, it also allows us to analyze the shapes of the stimuli that we see and determine the colors of the objects or landscapes that we witness, detect movements, analyze distances, etc.
How does the visual system work?
When we receive one or more visual stimuli (for example an object, a person, a landscape…), this information first reaches the retina, a tissue that is located on the surface of the eye and is sensitive to light. The retina is the main receiving organ of vision.
Subsequently, the visual information reaches the rods and cones, which are photoreceptor cells (“the vision cells”), which allow the processing of colors, shapes, lights, etc. These connect with other cells, the bipolar cells, and these, in turn, with the ganglion cells. The axons of the ganglion cells form the so-called optic nerve.
The optic nerve reaches another structure, the optic chiasm, and from there to the lateral geniculate nucleus of the thalamus, an area of the brain that has six layers. Finally, from there the information is sent to the primary visual cortex, located in the occipital lobe, and this lobe begins to operate, processing visual information and allowing us to “see”.
2. Perception and calculation
The occipital lobe is also related to visuoconstructive, visuoperceptive, and visuospatial functions , in addition to computational and mathematical processes.
On the other hand, this lobe also includes association areas or brain structures, responsible for integrating information from one or more sensory modalities.
injuries
The lesions that occur in each cerebral lobe produce a series of consequences and clinical manifestations in those who suffer from them; logically, each injured lobe will imply some consequences or others.
Occipital lobe injuries are diverse, depending on the specific area of the lobe that is damaged or affected . Although most of them are related to alterations in vision, in reality it is more complex. We are going to divide the different areas of the occipital lobe and the alterations or symptoms that an injury entails in each of them:
1. Primary visual cortex
If the lesion occurs in the primary visual cortex, two situations can occur: the lesion may be unilateral (affecting only one side of the brain or hemisphere) or bilateral (affecting both sides). In the first case, a homonymous hemianopia contralateral to the lesion will occur; this means that the patient will not be able to see a part of one of the visual fields.
On the other hand, if what occurs is a bilateral lesion, cortical blindness will appear; this means that the patient will not be able to see anything, they will only be able to perceive lights and movement. Cortical blindness occurs even when the visual organs are intact (the eyes, the optic nerve…) .
2. Primary visual cortex + underlying association area
If, in addition to the primary visual cortex, its underlying association area is injured, the so-called “Anton syndrome” will occur . This syndrome is characterized by the following symptoms: cortical blindness (already mentioned), anosognosia (ignorance or non-recognition of one’s own symptoms) and confabulation (invention of details, stories or stories with pure conviction).
3. Occipito-temporal region
A lesion in the occipito-temporal region, another specific area of the occipital lobe, will cause hallucinations and visual illusions . These symptoms appear more frequently in lesions that occur in the right hemisphere of the brain.
4. Right or bilateral visual association cortex
As we have already anticipated, the occipital lobe includes some association areas . If the lesion occurs in the visual association cortex, either in the right hemisphere or in both (bilateral lesion), the following symptoms will appear: apperceptive visual agnosia and prosopagnosia.
Apperceptive visual agnosia consists of an alteration of the elements that form a stimulus; For its part, prosopagnosia consists of the inability to recognize familiar or familiar faces (of relatives, friends, even oneself, etc.). Specifically, this last alteration is produced by a parieto-temporo-occipital lesion (POT area).
5. Left visual association cortex
A lesion in this same association zone that we mentioned, but in its left hemisphere, implies the following symptoms.
Associative visual agnosia (alteration between what we perceive and its meaning), optic aphasia (difficulties in describing or naming what is seen), color anomie (inability to name colors), alexia (partial or total loss of the ability to read ) and acalculia (partial or total loss of numerical understanding and calculation capacity).
6. Bilateral parieto-occipital region
The last region of the occipital lobe that we are going to discuss and that can also suffer damage, is the POT region. If the injury occurs bilaterally, “Balint Syndrome” originates.
Balint syndrome includes the following symptoms: simultagnosia (inability to recognize simultaneous objects), optic apraxia (inability to fix one’s gaze on a stimulus), and optic or visuomotor ataxia (lack of coordination between the hand and vision).
References
- Carslon, N.R. (2005). Physiology of behavior. Madrid: Pearson Education.
- Perea, M.V. & Ladera, V. (2015). Visual Agnosias: Agnosia for Objects, Simultagnosia, Agnosia for Color, pure Alexia. Journal of Neuropsychology, Neuropsychiatry and Neurosciences, 15(1): 9-30.
- Netter, F. (1989). Nervous system. Anatomy and physiology. Barcelona: Salvat.
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