Visual‌ ‌Cortex‌

Overview:

The brain is an essential component of the human body because it conducts vital functions and controls nearly all bodily functions. Each part of the brain is specialized to perform a particular task and to understand this complex working of the brain, it has been divided into many different chambers so that its numerous complicated processes can be better interpreted.

The brain has four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe. As it is obvious from the name, the occipital lobe is responsible for visual data processing. The visual cortex is present in the occipital lobe of the primary cerebral cortex that is located in the brain’s most posterior area. The visual pathway starts at the retinas of the eyes and ends up in the visual cortex of the brain for image processing and interpretation.

In this article, the location, structural components, function, and clinical complications involving the visual cortex are discussed.

Summary:

• The visual cortex is present in the posterior region of the brain, in the occipital lobe, which is one of the four lobes of brain
• The nerve cells in the primary visual cortex are organized into sections with fairly similar characteristics
• These nerve cell columns are grouped to form assemblies known as modules. Every module includes a variety of neuronal columns required to analyse a particular region of the visual field.
• Both hemispheres have their visual cortex that gets data from the opposing eye. The right cortical areas interpret messages received from the left eye, whereas the left cortical areas interpret data from the right eye.
• When visual data is sent forward from the retina, it travels through the use of the optic nerve (that shortly becomes the optic tract) to the lateral geniculate nucleus of the thalamus
• Visual data from the retinas of the eyes travel to the visual cortex via the thalamus, where it synapses in a nucleus known as the lateral geniculate.
• This information is then passed from the lateral geniculate to V1, the very first region of the visual cortex
• Cortical blindness (CB) is described as a loss of vision ability caused by bilateral damage to the tissue of the striate cortex in the occipital lobes with perfectly natural pupillary light reflexes

Cerebellum, cerebrum, and brain stem are the three major divisions of the brain. The cerebrum is divided into two hemispheres: the cortex (grey matter) on the outside and the nucleus (white matter) on the inside (white matter).

The cortex is divided into four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe.

Frontal lobe: The frontal lobe is present in the front of the brain and extends back to a fissure called the central sulcus. The thought process, motor control, feelings, and language are all controlled by the frontal lobe. It incorporates the motor cortex, which is in charge of motion planning and coordination; the prefrontal cortex, which is in charge of higher-level brain function; and Broca’s area, which is involved in speaking.

Parietal lobe: The parietal lobe of the brain is situated directly behind the frontal lobe and is responsible for handling data from the body’s sensory experiences. It houses the somatosensory cortex, which is responsible for generating sensory input from throughout the body such as contact, heat, and discomfort. The somatosensory cortex is topographically organized, which implies that spatial relationships that exist in other areas of the brain are replicated in the somatosensory cortex. The cortex component that handles sensory input from the hand, for instance, is relatively close to the cortex component that processes data from the wrist area. 

Temporal lobe: The temporal lobe is present on the side of the head (as the word temporal indicates “close to the temples”) and is responsible for listening, recollection, feelings, and some language functions. The auditory cortex, the primary area that accounts for auditory data processing, is positioned within the temporal lobe. Wernicke’s area, which is necessary for speech perception and interpretation, is also stationed here.

Occipital lobe: The primary visual cortex, which is capable of processing input of visual data messages, is positioned in the occipital lobe that is located in the very back of the brain. The occipital cortex is organized retinotopically, which indicates that the location of an entity in an individual’s visual field is closely related to the location of that entity’s portrayal on the cortex.

The calcarine cortex, striate cortex, and V1 are all names for the primary visual cortex. It is the primary place of signal reception from the retina. It is found on the occipital lobe’s medial side, in the gyrus inferior and superior to the calcarine sulcus. The majority of the cortex is contained within the calcarine sulcus’s deep surfaces.

Location:

The primary cortical part of the brain that obtains incorporates, and processes visual information forwarded from the retinas of the eyes is the visual cortex. It is located in the occipital lobe of the primary cerebral cortex that is located in the brain’s most posterior area (Figure 1). The primary visual cortex is predominantly provided by the calcarine artery, but it can also be supplied by the parieto-occipital artery and the posterior temporal artery.

The primary visual cortex accounts for a tiny part of the visible cortex surface in the occipital lobe, but since it extends into the calcarine sulcus; it contributes to a significant portion of the cortical surface on the whole.

Structure:

Because of the presence of a high amount of myelinated axons that are located along the sides of the calcarine sulcus, the primary visual cortex is also known as the striate cortex. These axons are known as the line of Gennari (after the very first scientist who discovered them in the later part of the 1700s) causes the primary visual cortex to look striped.

The nerve cells in the primary visual cortex are organized into sections with fairly similar characteristics. For instance, nerve cells in one column may respond to stimuli received by the contralateral eye which have a specific orientation (for example, vertical vs. horizontal). Nerve cells in a different column may also respond primarily to upright direction, but this happens only when the data is relevant.

These nerve cell columns are grouped to form assemblies known as modules. Every module includes a variety of neuronal columns required to analyse a particular region of the visual field. As a consequence, the primary visual cortex contains several of these modules beneath the cortical surface to accomplish the visual scene.

Function:

Both hemispheres have their visual cortex that gets data from the opposing eye. To put it into simpler words, the right cortical areas interpret messages received from the left eye, whereas the left cortical areas interpret data from the right eye (Figure 2). The visual cortex’s primary aim is to acquire, categorize, and incorporate visual information. 

When visual data is sent forward from the retina, it travels through the use of the optic nerve (that shortly becomes the optic tract) to the lateral geniculate nucleus of the thalamus. It is then passed in a tract known as the optic radiation, which bends around the lateral ventricle wall in each cerebral hemisphere and returns to the occipital lobe.

Visual data from the retinas of the eyes travel to the visual cortex via the thalamus, where it synapses in a nucleus known as the lateral geniculate. This information is then passed from the lateral geniculate to V1, the very first region of the visual cortex. V1 is also called the primary visual cortex and it is located near the calcarine sulcus. The calcarine fissure, also known as the calcarine sulcus, is situated on the medial surface of the occipital lobe. It divides the visual cortex (also known as the calcarine cortex) into two parts. 

The direction of the fissure varies, but it is usually horizontal, and it joins the parieto-occipital fissure anteriorly and achieves a varying distance toward or further (and onto the lateral part) of the occipital pole. 

The visual cortex’s information generated is then sent to other parts of the brain to be analysed and used appropriately. This highly specialized procedure enables the brain to recognize objects and designs rapidly and without much deliberate awareness. One advantage of this specialization is that the rest of cortical regions, including those accountable for executive working and strategic decision forming are available to conduct other calculations. Even so, because visual processing is often unconscious, it can result in misinterpretations of visual information, as evidenced by the effectiveness of visual illusions.

The visual cortex’s main function is to interpret visual data input.  On the basis of structural and functional categories, the visual cortex is divided into five separate regions. According to theories put forward by scientists, it is believed that as visual data is disseminated along, each successive cortical area becomes more specialized than the one before. The visual cortex’s nerve cells frequently react to changes within a set receptive field or region of the visual field to which they react, and nerve cells in each visual region respond to various kinds of stimuli.

Simple and complex cells are two of the well-studied examples of specialized cells. Simple cells that are mostly found in V1 respond to specific visual cues like the alignment of corners and line segments. Complex cells, which emerge in V1-V3, respond to corners and directions in the same way that simple cells do, but they do not seem to represent a particular receptive range. They react towards the sum of many receptive visual fields that are incorporated from many simple cells. Furthermore, complex cells prefer to respond to motion in particular directions. 

V1 is the very first cortical area to gather and analyse data, and it is also the well-studied region of the visual cortex (Figure 3). V1 is divided into 6 distinct layers, each with its own set of types of cells and operations. Layer 4 is notable for receiving data from the lateral geniculate. Layer 4 also the region that has the largest amount of simple cells. Layers 2, 3, and 6 are where complex cells can be found.  V1 reacts to simple visual cues like alignment and trajectory. The accumulation of this data lays the groundwork for more complex pattern information processing afterward in the visual stream.

V2 collects integrated data from V1 and has a higher degree layer of complexity and reaction flow to objects as a consequence. Cells in this area have been documented responding to changes in colour, spatial frequency, relatively complicated patterns, and orientation of different things.  

V2 communicates with V1 via feedback links and has information forwarding connections with V3-V5. The documentation exiting the second visual region is divided into the ventral and dorsal streams, which exist in specific aspects of visual data processing. The former is commonly described as related to the recognition of objects whereas the latter is considered to be related to spatial functions and visual-motor skills. There are more specialized cells are involved as visual data spreads throughout the brain. According to the hypothesis, there are specialized cells or groups of these cells that understand to deal with particular objects, allowing for the rapid recognition of earlier seen items. Moreover, similar cells may be in charge of other essential visual data, like spatial orientation.

Complications involving the visual cortex:

Cortical blindness (CB) is described as the loss of vision ability caused by bilateral damage to the tissue of the striate cortex in the occipital lobes with perfectly natural pupillary light reflexes. Cortical blindness is a subtype of cerebral blindness characterized as visual impairment injury to the visual pathways posterior to the lateral geniculate nuclei.

Both adults and children can be impacted by cortical blindness. Common causes in children usually involve:

• Occipital lobe congenital abnormalities
• Physical brain damage to the brain’s occipital lobe
• Perinatal Ischaemia: Perinatal hypoxia-ischaemia (H/I) is defined as exposure to low amounts of oxygen and reduced flow of blood just before, during, or after birth and is thought to be the leading cause of neurodevelopmental deficits in term and preterm infants.
• It is observed in adults with lesions of the primary visual cortex of the occipital lobes as a result of a variety of diseases, which include:
• It is observed in adults with lesions of the primary visual cortex of the occipital lobes as a result of a variety of diseases, which include:
• Hypoglycaemia (It is a condition in which the blood sugar level is extremely low)
• Stroke
• Embolism of the heart
• Hyponatraemia (Hyponatraemia is a situation in which there is insufficient sodium in the blood)
• Epilepsy of the occipital lobe
• Creutzfeldt-Jakob disease (Creutzfeldt–Jakob disease (CJD), also recognized as subacute spongiform encephalopathy or neurocognitive disorder caused by prion disease, is a lethal degenerative condition. Memory problem issues, behavioral issues, lack of coordination, and visual disturbances are among the early symptoms)
• Eclampsia
• Infection, for example, HIV 
• MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes)

Aside from standard management of the underlying cause, which is most often stroke, the clinical course is visual coaching and rehabilitative services. Compensation therapy, restitution therapy, and substitution therapy are three frequent kinds of interventions. To fully heal from visual field deficits, restitution therapy is used. It’s similar to perimetry (An individual’s field of vision is quantified). In this case, the patient notices various light spots on a black screen that span the blind and normal visual hemifields.

Compensation therapy compensates for vision problems through saccadic eye movements. It aids in the capture of visual stimuli that would otherwise be lost in the blind area of the visual field. Substitution therapy employs prisms or other gadgets to project the sensory input from the normal to the blind side of the field of vision. 

Conclusion:

Like all the other parts of the brain, the visual cortex plays a huge role in interpreting one of the senses of the body (vision). It is located at the posterior end where it efficiently serves its role in visual interpretation and processing by the brain along with several types of cells. The primary cortical part of the brain that obtains incorporates, and processes visual information forwarded from the retinas of the eyes is the visual cortex. Visual data from the retinas of the eyes travel to the visual cortex via the thalamus, where it synapses in a nucleus known as the lateral geniculate. This information is then passed from the lateral geniculate to V1, the very first region of the visual cortex. V1 is also called the primary visual cortex. Cortical blindness (CB) is described as the loss of vision ability caused by bilateral damage to the tissue of the striate cortex in the occipital lobes with perfectly natural pupillary light reflexes. Aside from standard management of the underlying cause, the clinical course is visual coaching and rehabilitative services.

Reference list

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