Occipital Lobe

The occipital lobe is the seat of most of the brain's visual cortex, allowing you not only to see and process stimuli from the external world, but also to assign meaning to and remember visual perceptions. Located just under the parietal lobe and above the temporal lobe, the occipital lobe is the brain's smallest lobe, but its functions are indispensable.

Where is the Occipital Lobe Located?

Understanding the occipital lobe requires a basic understanding of brain anatomy. The cerebral cortex of the brain—a part of the brain shared by all vertebrates—is the newest part of the brain, evolutionarily speaking. All mammalian brains have four distinct lobes, but the brain itself—as well as the lobes it contains—is divided into right and left hemispheres. This means that each lobe can actually be divided into two parts. The occipital lobe includes a right and left lobe that interact with one another, each controlling a range of visual functions.

Like other lobes of the brain, the occipital lobe does not have clear internal boundaries separating it from the rest of the brain. Instead, neuroscientists use the skull's bones as their guide, so the occipital lobe rests underneath the occipital bone.

The occipital lobe is the rearmost lobe of the brain, located in the forebrain. It rests upon the tentorium cerebelli, a thick membrane of tissue the separates the cerebrum from the evolutionarily older cerebellum.

What Does the Occipital Lobe Do?

Studying the brain is a difficult task, particularly since some areas compensate for others when the brain suffers damage. The brain's sensitive, dense, and complex nature means that researchers are constantly uncovering new structures within the brain, and new functions for each brain lobe. The occipital lobe is no exception to this rule.

Researchers once thought that the occipital lobe only controlled visual functions. But in recent years, they discovered that some portions of this lobe receive inputs from other brain regions. Specifically, a brain region called the dorsomedial stream receives input both from regions of the brain related to vision, and to areas that are not linked to visual processing. This suggests either that the occipital lobe may perform additional functions, or that researchers have not identified all regions of the brain associated with visual processing.

Although we know that the occipital lobe is dedicated to vision, this process is highly complex, and includes a number of separate functions. Those include:

• Mapping the visual world, which helps with both spatial reasoning and visual memory. Most vision involves some type of memory, since scanning the visual field requires you to recall that which you saw just a second ago.
• Determining color properties of the items in the visual field.
• Assessing distance, size, and depth.
• Identifying visual stimuli, particularly familiar faces and objects.
• Transmitting visual information to other brain regions so that those brain lobes can encode memories, assign meaning, craft appropriate motor and linguistic responses, and continually respond to information from the surrounding world.
• Receiving raw visual data from perceptual sensors in the eyes' retina.

What Are Some Important Structures in the Occipital Lobe?

Like all other lobes of the brain, the occipital lobe contains a number of structures and neuronal tracts that work together to enable vision. Those include:

• Brodmann area 17: Known as V1, this region is located in the occipital lobe's calcarine sulcus, and serves as the brain's primary visual cortex. It aids the brain to determine location, spatial information, and color data.
• The ventral stream: Known sometimes as V2, this is a secondary visual cortex that helps the brain assign meaning to what it is seeing. Without V2, you would still be able to see, but would have no conscious awareness of or understanding of the sights your eyes took in.
• The dorsomedial stream: Neuroscientists don't yet have a strong understanding of this brain region, which connects to both V1 and V2, as well as other brain regions.
• The lateral geniculate bodies: These structures take in optic information from retinal sensors in each eye, sending raw information to each visual cortex.
• Lingula: this area receives information from the contralateral inferior retina to gather information about the field of vision.

Brain imaging studies have revealed that neurons on the back of the gray matter of the occipital lobe create an ongoing visual map of data taken in by the retinas.

How Does the Occipital Lobe Interact With Other Areas of the Body?

No part of the brain is a standalone organ that can function without information from other parts of the body. The occipital lobe is no exception. Although its primary role is to control vision, damage to other brain regions and body parts can inhibit vision. Moreover, some evidence suggests that, when the occipital lobe is damaged, nearby brain regions may be able to compensate for some of its functions. The occipital lobe is heavily dependent on:

• The eyes, particularly the retinas, which take in and process visual information to then be further processed by the occipital lobe. 
• The frontal lobe, which contains the brain's motor cortex. Without motor skills, the eyes cannot move or take in information from surrounding regions. 

• The temporal lobe, which helps assign meaning to visual information, in addition to encoding it into memories.

How Does Damage to the Occipital Lobe Affect Functioning?

The most obvious effect of damage to the occipital lobe is blindness, but occipital lobe damage can have other surprising effects:

• Epilepsy: Some seizures occur in the occipital lobe, and occipital lobe damage increases vulnerability to seizures.
• Difficulties with movement: Even if you are still able to move, changes in depth perception and vision can lead to inappropriate movements and difficulty navigating the visual field.
• Difficulties perceiving colors, shape, dimension, and size.
• Difficulty recognizing familiar objects or faces.
• Hallucinations
• Inability to recognize or read written words.
• Inability to detect that an object is moving.
• Difficulty reading or writing; for example, the words may appear to move on the page.
• Difficulty locating objects within the environment, even when you are able to see those objects.
• Difficulties with fine and gross motor skills, as well as balance.