The heavily folded surface of the cerebrum forms the lobes of the cerebral cortex, which are responsible for processing different types of sensory information. The lobes get their names by the bones that overlie them.
The occipital lobe is one of the four major lobes located in the cerebral cortex, but it’s smallest in size. As its name implies, it’s protected by the occipital bone of the skull, and its primary function is vision.
Where Is The Occipital Lobe Located?
The occipital area of the skull is located right above the neck, at the back of the head, so the occipital lobe lies behind the parietal and temporal lobes. It’s positioned at the back of both brain hemispheres, which is why there are two occipital lobes, one in each of the brain hemispheres.
To be more precise, the two occipital lobes are located in the prosencephalon, i.e. the largest part of the brain, also known as the forebrain. This is a region that accommodates the center for vision – an area of the brain which receives the visual information through the retina of the eyes.
They interact with one another, controlling various visual functions. For instance, the left half of each eye sends information to the left hemisphere of the brain, and the right half of each eye sends information to the right hemisphere of the brain where the information is further processed.
Anatomy and Structure of the Occipital Lobe
The occipital lobe consists of numerous composite structures labeled as: occipital sulci, occipital gyri, fissures, and a cuneus.
The gyri (Sg. gyrus) is the raised surface (or ridges) of the brain that gives it its familiar folded structure.
The sulci (Sg. sulcus) are the fissures that run between them. They are made of the gray matter of the cerebral cortex, consisting mainly of nerve cells.
The characteristic folded surface of the brain, which is created by the gyri and sulci, increases the surface of the cerebral cortex, thus increasing the number of cortical neurons that transfer the sensory information to the corresponding centers of the brain.
This way, these structures increase the processing power of our brain, i.e. they improve our learning function by giving way to more connections among the neurons.
Since there is no clear border to separate it from the other parts of the brain, there’s a thick membrane called tentorium cerebelli (or cerebellar tentorium) that separates the occipital lobe from the cerebellum.
The two occipital hemispheres of the occipital lobe are divided by a longitudinal cerebral fissure – the deep furrow that divides the brain into a left and right hemisphere.
The occipital gyri are three in number, placed parallel on the side of the occipital lobe. A more detailed anatomical analysis displays the following constitutional elements of the occipital lobe:
- Lateral-occipital (fusiform) gyri – This fusiform gyrus is part of the occipital lobe in Brodmann Area 37, also known as the occipitotemporal area 37 (H).
- Lingual (infra-calcarine) gyrus – The gyrus on the occipital lobe that form the lower part of the calcarine sulcus. Together with the cuneus, they form the visual cortex.
- Medial occipitotemporal (fusiform) gyrus – These gyri consist of temporal and occipital gyri. They are considered to be relevant for the process of recognition, as well as for some neurological conditions, such as dyslexia.
- Cuneus – Cuneus is a smaller lobe within the occipital lobe of the brain which receives and processes visual information.
- Parieto-occipital sulcus – It’s located near the end of both brain hemispheres, and divides the occipital and parietal lobes in both the left and right side of the brain.
- Calcarine sulcus – It separates the cuneus (above) from the lingual gyrus (below). The primary visual cortex (Brodmann area 17) is located in a part of this gyri.
- Preoccipital notch – A notch on the lower margin in front of the occipital pole which serves as an important anatomical landmark of this part of the brain, since the occipital lobe is located right behind it.
What Is The Function of the Occipital Lobe?
The occipital lobe is mainly concerned with analyzing and interpreting visual information from sensory nerve signals sent by the eyes. It is responsible for receiving, selecting, organizing, processing, and integrating the visual signals received through the retina of the eye.
The processes that take place within the occipital lobe are numerous since vision is one of the most complex and vital of bodily functions. The occipital lobe’s functions are:
- Identification of the visual stimuli and signals
- Receiving information from the retina of our eyes
- Processing visual information
- Determining the field of vision and the objects within the field
- Assessment of distance, depth, and size of both the visual field and the objects within the field
- Transferring visual information to other parts of the brain
- Control and regulation of the sense of sight
- Determining colors of the object in the visual field
- Recognizing people/faces
- Reading
- Reading comprehension
All these processes are controlled and regulated in the occipital lobe. However, sending information from the primary visual cortex (the receiving center) to the visual association cortex (the interpretation center) is the single process that incorporates all the above-mentioned processes, and, as such, is one of the main functions of the occipital lobe.
What Are the Functions of Both the Primary Visual Cortex and the Visual Association Cortex?
The primary visual cortex (also known as Brodmann area 17 or V1) presents the visual area of the cerebral cortex where the visual information about static and moving objects is first received and processed. It is located in and around the calcarine fissure in the occipital lobe.
This visual area contains a sort of map where the visual field of the eyes is projected, i.e. everything in scope of our sight is directly processed in the V1 area of the occipital lobe.
While the primary visual cortex deals with the recognition of basic visual information (location, edges, light or dark, etc.), the visual association cortex (Brodmann areas 18 and 19) is part of the cerebral cortex which processes the visual information.
Together, these two areas of the occipital lobe create our visual world.
The Functions of Brodmann Areas 17, 18, and 19
Brodmann area 17 is the first visual area in the cerebral cortex where visual information is processed. It directly receives the visual information from the lateral geniculate nucleus – the primary center which receives the information from the retina of our eyes.
Brodmann areas 18 and 19 are located in the visual association cortex and serve for recognition of the visual stimuli we receive through our eyes. Also, this is where the occipital lobe conducts the processes of visual recognition of faces, animals, or objects.
These areas in the occipital lobe integrate the visual information, thus helping us understand and define what we see by connecting the given information to an image stored in our memory.
How Does Our Brain Understand What We See?
The process of assigning meaning to the visual images around us starts with the eyes. We receive visual stimuli for the brain through the retina of our eyes,.
This visual information then travels to the back of our head (where the occipital lobe is located) with the help of neurons from the visual center of our brain to the temporal lobe. The temporal lobe is an integral part of this complex process, because it helps us understand what we are seeing.
Next, the occipital lobe transfers the visual information to the frontal and the parietal lobe. These lobes are responsible for giving meaning to the stimuli (or translating what we see to the brain), as well as triggering our response to it.
As a result of these complex and subsequent processes, we can tell what is in front of our eyes and within our field of vision, what’s its color and shape, what’s our distance from it, and whether the object is moving or not.
What Happens When the Occipital Lobe Suffers an Injury?
Since the occipital lobe is responsible for making sense of the things we see, any injury to it would mean loss of our ability to process visual information correctly.
Injuries to the occipital lobe mainly occur after a strong hit at the back of the head. These injuries can lead to some of the most severe health problems, including loss of vision or blindness.
But, the list of the medical conditions and health difficulties is much longer, which proves the vital functions of the occipital lobe. It includes the following:
- Defects in vision
- Loss of vision
- Difficulty locating objects in the environment
- Difficulty identifying colors (visual agnosia)
- Hallucinations
- Inaccurate seeing of objects
- Inability to recognize words
- Inability to recognize drawn objects or patterns
- Inability to recognize the movement of an object (movement agnosia)
- Difficulty in both reading and writing
The symptoms of a possible injury to the occipital lobe range from strong headache, dizziness, weakness, tingling sensation at the back of the skull, to photophobia and paralysis.
To Sum Up
Located at the lower back side of the brain and protected by the occipital bone of the skull, the occipital lobe hosts the visual center of the human brain.
The occipital lobe may be the smallest one of the four major lobes in the cerebral cortex, but it regulates the complex process of creating our vision by receiving and processing visual stimuli from the retina of our eyes.
The visual signals are further transmitted to the primary visual cortex and the visual association cortex (i.e. to the corresponding Brodmann areas). At these locations, they are regulated and controlled in a manner which helps us recognize people, faces, objects, colors, shapes, and sizes.
Furthermore, the visual center of the occipital plane aids our reading, comprehension, and assessment of the distance, depth, and size of both the visual field in front of our eyes and the objects within it.
In this way, we are able to visually locate the distance from one point to another, tell the shade of a color, the structure of an object, recognize our friends and relatives, and read.
However, without a healthy occipital lobe, our ‘visual center’ would be powerless and we would be deprived of its ‘superpowers’ which help us perceive the world around us.
Fun Facts
Did you know?
- The primary visual cortex is the area of the brain which is responsible for our recognition of patterns.
- The primary visual cortex also serves as a map of the spatial information received from the visual signals through the retina of our eyes.
- Even though the occipital lobe is well protected under the skull, an injury of the occipital lobe can lead to blindness, hallucinations, or illusions.
- The characteristic furrowed appearance of the brain is created by the structures called sulci (fissures) and gyri (ridges).
- The occipital lobe helps us understand what we have seen, by linking the visual information we get through our eyes with the images stored in our memory.
- The occipital lobe is the part of the brain which helps a child understand the world that surrounds it by transforming the things it sees into images the brain can understand.
- The occipital lobe makes only 18% of the human brain.
- Just imagine how super-fast is the process of receiving visual information through our eyes, its instant ‘delivery’ to the visual center of the brain located in the occipital plane, and getting an image, as well as an information for it… Incredibly fast, isn’t it?
- When you look at a lemon and recognize it by its yellow color, this is done with the help of the occipital plane in your brain.
- Our eyes and brain function like cameras – everything we see becomes registered and stored in the memory of our brain.