Have you ever hit the back of your head and your eyesight becomes cloudy?

The occipital lobe is responsible for one of the five senses, vision. It processes all the stimuli received from the retina. Therefore, any blow to this area can alter your eyesight or even state of consciousness.

Vision is indispensable in our daily lives and, despite how innate it is to see, vision is the end result of the integration of many structures of the brain.

Here we tell you about the neuroanatomy and functions of this important brain lobe.

What is the occipital lobe?

The surface of the human brain is not smooth, we can find depressions and folds along it. Each of these structures has its own nomenclature.

Deep depressions are called fissures and divide the brain into regions called lobes. Surface depressions are called grooves and divide the lobes into convolutions or gyres.

The occipital lobe is the most posterior of all (i.e., located in the rear of the brain). The parietoccipital fissure separates the occipital lobe and the parietal lobe, and the preoccipital incisura separates it from the temporal lobe.

A layer of tissue called the cerebellum tent separates the occipital lobe from the cerebellum, located just below it.

Alterations of the occipital lobe are associated with the creation of visual illusions or hallucinations.

Structure of the occipital lobe

Each lobe is composed of anfractuous or irregular elevations, which are the turns. Each turn or groove contains specialized neurons that fulfill a function.

Below, we mention some of the most outstanding.

Calcarine Fissure

On the medial surface of the occipital lobe, we find the most relevant structure in it: the calcarine groove or fissure.

It starts from the parietooccipital groove to the occipital pole (which corresponds to the most rear portion of the lobe). Deep in the sulcus, it is the seat of the primary visual cortex (which we will see later).

Also, it divides the medial surface of the lobe into two gyri: the cuneal (or superior) and the lingual (or inferior).

Occipital cerebral cortex

Under the microscope, most lobes share similarities. They are divided into areas or strata, in general there are six, but it varies from zone to zone.

In them, all kinds of cells are located. The neurons, in charge of transmitting the nervous impulse, cell bodies in charge of regulating the functions of the neurons, and the glial cells, the support that keeps the cytoarchitecture in place.

But, there are differences with other anatomical regions. Under the microscope, bands of myelin are seen along the fourth layer of the occipital lobe (as we will see later).

Primary Visual Area

The calcarine groove, the cuneal and lingual gyrus form a whole, called the primary visual cortex.

They are responsible for receiving nerve impulses from the lateral geniculate body (cellular nucleus found in the thalamus, whose function is to transmit information from the brain stem to the cerebral cortex).

The primary visual area is also called V1 or Brodmann’s area 17. It sends the information captured by the retina to the secondary visual area.

The visual area, in its entirety, is divided into more than a dozen regions starting from V1, V2, V3 and so on. However, the most studied areas are the first two.

It is hypothesized that each presents a group of cells more developed than the other and that they perceive specific visual stimuli.

secondary visual area

Also called Brodmann area 18 and 19. It corresponds to area V2 of the visual cortex, that is, they contain highly specialized cells.

It surrounds the primary visual area and receives information from the latter through the dorsal and ventral stripes.

However, this communication is not unilateral. It means that the secondary area not only receives information from the primary, but also sends information to the latter, acting as a feedback loop.

V2 sends signals to V3 and in turn to V2.

Tertiary Visual Area

Surrounds the previous area and receives information from it. Under the microscope, it has many similarities to area V2, however there are notable differences.

Among these, that the cells show a greater degree of specialization, focused on interpreting the complexities of the object to be observed. For example, its position in space, as well as its colors and shapes.

The V3 area is made up of other much more specific ones such as V3A. In turn, it sends information to V4. In turn, it sends feedback signals to area V2.

As we have mentioned, there are many cortical areas in charge of vision processing, whose functions have not yet been fully elucidated.

Stripe Bib

The dorsal and ventral fringe are the communication pathways that transmit neural signals from the visual cortex to other regions of the brain.

The dorsal stripe sends visual information to the parietal lobe. It is hypothesized that it is in charge of motor tasks and visual motor coordination.

Therefore the way to handle each object according to its intrinsic characteristics, that is, its shape, size, surface, and much more.

The way you take a baby in your arms is not the same way you take a shoebox or a newspaper. This is achieved thanks to the integration of different areas of the brain.

ventral strip

The ventral strip sends the information to the temporal lobe. Its function is the recognition, perception and identification of objects based on their physical properties.

That is, recognizing a cup of tea, a pencil or a telephone based on its shape, size and colour, as well as being able to differentiate one from the other.

Gennari’s striae

Gennari’s striae or occipital striae is called a layer of neurons whose axons and dendrites have myelin. In this case, it would be the fourth layer of the cortical architecture of area V1.

Myelin is a protein secreted by glial cells that surround the endings or branches of neurons, modifying the conduction speed.

Due to the high amount of myelination, streaks or bands are observed both under the microscope and with the naked eye. The endings of the neurons that come from the thalamus and the neurons whose endings go to the V2 area are observed.

Characteristics of the occipital lobe

Each lobe has unique characteristics that set it apart from the other lobes of the braintag. The occiput is no exception.

We present some of its most outstanding features.

It is shaped like a pyramid

The topographic limitations of the occipital lobe give it a pyramidal shape.

On the medial surface of the lobe its limit is the parietooccipital sulcus. On the lateral side, its border is an imaginary line that starts from one end of the occipital parietal groove to the preoccipital notch.

Finally, on its underside, it is another imaginary line that starts from the preoccipital notch to the opposite end of the parietooccipital sulcus.

It is the center of vision

The occipital lobe is the morphological seat where visual stimuli are received, coming from the lateral geniculate nucleus in the thalamus, which in turn receives it from the retina.

Once visual stimuli reach the visual cortex, they are processed and interpreted. The visual cortex goes beyond seeing, it integrates all the sensory components and provides the person with the full picture of their surroundings.

That is, associate what is observed with a memory, a sound, texture and much more.

An injury to this area can lead to cortical blindness, but this is not always the case. They can also cause prosopagnosia, the inability to recognize people’s faces.

It is smaller than the rest of the lobes

The size of this lobe, compared to the rest of the lobes, the occipital lobes are the smallest.

Astudypublished in the Archives of Neuro-Psychiatry analyzed a number of occipital lobe specimens. The distance between the preoccipital incisura and the occipital pole (the most posterior portion of the brain) averaged between 30 and 61 mm.

In comparison, the frontal lobe occupies35-38.5% of the cerebral hemispheres.

Has a specialized and effective function

The neuronal population of the occipital cortex is highly developed, with the purpose of fulfilling specific functions, such as the interpretation of the size, shape or color of objects.

It is hypothesized that each region of the visual cortex presents a greater complexity than the previous area (ie, the neurons of V1 are less specialized than those of V2).

It occupies 12% of the neocortex

Throughout evolutionary history, the human brain has developed, bringing with it a plethora of new and complex functions that our ancestors lacked.

The neocortex is the most recently developed brain region, from an evolutionary point of view. It is responsible for functions such as sensory perception, cognition, and complex motor tasks.

The occipital lobe corresponds to only 12% of the neocortex. However, aStudy published by the Department of Neurology and Radiology at Massachusetts General Hospital shows different figures.

The scientific group carried out a scan, using magnetic resonance imaging, of the brains of twenty young adults. In these, the occipital lobe represented 18.3% of the neocortex.

It has not evolved over time

As we explained, the development of new cortical areas in the neocortex have provided higher-grade cognitive functions to humans and, to a lesser extent, to primates.

However, the visual area is a topographic region of the brain that can be found in hundreds of other mammals of lesser degree, such as the tenrecidae.

Although most mammals lack a highly developed neocortex, they do share a number of similarities: they have a primary and secondary somatosensory cortex, as well as a visual cortex.

These findings point to an archaic common origin. In fact,macaques and humans present similarities in terms of cytoarchitecture, function, and neuronal population in the visual area.

Functions of the occipital lobe

In the occipital lobe we find the part of the cerebral cortex in charge of the visual area, by processing the information that enters through the eyes.

Among the multiple functions of the occipital lobes, we will describe the most relevant and how information is processed from the visual cortex in the brain.

Captures nerve impulses from the eyes

In each of our optic nerves we have approximately one million neural nerve fibers that are responsible for carrying visual information to the central nervous system.

The occipital lobe, through the primary visual area (Brodmann’s area 17), picks up nerve impulses from the eyes.

The retina is the light-sensitive portion of our eye and inside it is made up of the cones and rods.

These cells are responsible for specialized functions. The rods detect dim light and are basically responsible for black and white vision, and vision in the dark.

These cells when excited transmit nerve impulses from the retina to the fibers of the optic nerve. Following that, they pass into the lateral geniculate body, which sends the afferent fibers to the visual cortex.

These fibers first pass forward in the white matter of the temporal lobe, and then turn to the primary visual cortex in the occipital lobe.

Analyze visual information

In the occipital lobe is the secondary visual area also called Brodmann areas 18 and 19. These surround the primary visual area on the medial and lateral surfaces of the cerebral hemisphere.

In turn, there are more areas that are in charge of specialized and specific features, such as the location of the object in space, its relationship with the other elements that we observe, direction, limits and much more.

Boosts memory and visual memories

The secondary visual area is in charge of analyzing the information in greater detail.

An example would be relating said information to visual memories of the past, thus boosting the person’s memory so that they perceive and recognize what they are seeing.

This is achieved by integrating the visual stimulus with the memories stored in the limbic system.

Recognize and interpret images

Our eyes transform the nerve impulses that excite cells in the retina into action potentials on the optic nerve, and then they are driven to the visual cortex, where they are processed. Giving rise to the sense of sight.

Refraction is the inclination of light rays as they pass from one medium to another that has a different density. This allows the focusing of an accurate image on the retina.

The transformation of visual information into an electrical impulse (and its processing in the occipital lobe), is divided into the formation of three images.

The first is formed thanks to the action of light on the photoreceptors. This is changed to a second image by the bipolar cells and finally converted to a third image by the ganglion cells.

The final image is transmitted to the lateral geniculate bodies and eventually reaches the cortex of the occipital lobe.

Information is transmitted from the primary visual cortex through two pathways: the dorsal and ventral stream.

The ventral stream is the one that has associations with object recognition and transmits visual information to the temporal lobe, specifically Wernicke’s language-sensitive area.

Thus demonstrating that the lobes of the human brain work together.

Identify movements and colors

The way the human brain perceives colors is a complex phenomenon.

This depends on the adaptation of the retina to light, the source of illumination and the light reflected by objects.

The occipital lobe can discern the hue, intensity, and saturation of a color.

Although color is processed in V1, in the human brain (and other primates) electrical activation of other areas, such as V2, V3, V4, and V5/MT, and even V8, has been detected invivo studies.

Everyone is involved in color processing: intensity, hue, saturation, color direction, where a color starts and ends.

Stimulates thoughts and emotions

The vision is integral in many aspects. When we look at a painting that moves us, we feel happiness and wonder. In the opposite case, if we observe something we don’t like, it awakens a feeling of displeasure.

The visual cortex is not a hermetic area, but interconnected with the rest of the brain to achieve complex functions, especially with the limbic system, in charge of modulating our emotions.

Witnessing an event that really bothers us can inhibit any function of the frontal lobe, which is responsible for regulating our social behavior.

Observing something that terrifies us is another clear example of visual integration with the rest of the brain. Blood pressure and heart rate rise, breathing increases, and even our body does not respond to our orders.

Allows spatial recognition and orientation

As we mentioned before, the primary visual cortex, located in the occipital lobe, transmits information through two pathways: a ventral stream or fringe and a dorsal stream.

In which this dorsal current is responsible for the location of the object and carries visual information to the parietal lobe.

In the parietal lobe, sensory data is integrated to provide a coherent image of ourselves allowing spatial and environmental recognition, thus orienting us in the place we are.

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