Occipital Lobe Definition

The shortest among the four lobes, the occipital lobe is responsible for vision processing and remembering. It is located in the rear of the brain. The occipital lobe, situated behind the temporal and parietal lobes, contains the primary and secondary visual cortices as well as connections towards the retinas of the eyes. This portion of the brain is found in all vertebrates and is the latest development in evolution.

Occipital Lobe Location

The occipital lobe is placed posterior to the parietal and temporal lobes and somewhat over the cerebellum, near the rear of the skull. Despite being the furthest away from the eyes, this portion of the cerebral cortex is critical for vision. The occipital lobe, like all other lobes of the brain, is divided into two hemispheres. Both lobes interact continually, allowing humans to view entire, three-dimensional situations rather than flat pictures.

Elephants do not have a well-developed occipital lobe, having unusually huge temporal lobes instead (however, their neural tissue is somewhat less thick than ours). Elephants are known for their communication skills and reliance on their senses of scent and sound, all of which are temporal talents. Elephants, on the other hand, have weak vision and can only see for around twenty metres. Of all animals, humans and apes have the sharpest eyesight (clarity of vision).

Occipital Lobe Function

Occipital lobe function includes acquiring optical inputs via the retinas of the eyes, interpreting this data, connecting what is viewed with our optical memories, and passing this analysed information to other brain regions. Many individuals assume that images of one eye are sent to the opposite hemisphere of the brain. This is not the case. To begin with, our eyesight is divided between the left and right hemifields—think of chopping both eyes in half vertically. The visual data processed by both retinas’ left sides is isolated from the visual data processed by both retinas’ right sides.

The right hemisphere of the brain is responsible for what we see with our left eye. A plant towards the left of your sight line is captured via the right sides of each retina. You can see how the eyes are divided into green and red. The line coming through the right sides of both retinas terminates near the right primary visual cortex. However, red appears on the left as well as green on the right in the visual field. They’ve switched over.

The occipital lobe is subdivided into portions designated V1 through V5, which have been shared by the primary and secondary visual cortices.

The optic nerve and the thalamus provide information to the main visual cortex (V1). Regions V2 through V5 make up the secondary visual cortex. The main visual cortex sends information to the secondary visual cortex through dorsal or ventral channels. The dorsal route sends information to the parietal lobe of the brain concerning the position of a viewed item. The ventral route transports data to brain regions involved in recognition and memory. The main and secondary visual cortex’s functions are detailed in further detail below.

Primary Visual Cortex Function

The striate cortex is another term for the main visual cortex. Which part of the occipital lobe is the largest and most striped? Visual information is classified and transferred to the secondary visual cortex after it arrives at V1. Through dorsal and ventral visual pathways, the secondary visual cortices deliver specialised information to the parietal or temporal lobes.

Without going into too much detail, pictures collected on the retina are conveyed to the main visual cortex through the optic nerve. The primary visual cortex subsequently decides which data to send to the temporal lobe through the ventral visual channel and which information should be sent to the parietal lobe through the dorsal visual pathway. It’s comparable to a mail sorting facility. The temporal (ventral) and parietal (dorsal) streams are the ventral and dorsal routes, respectively. Consider the parietal lobe to be a continuation of the line of the spine – a dorsal location – to recall which stream is which.

Secondary Visual Cortex Function

The secondary visual cortex’s job is to take V1’s classified visual information and analyse it further. The visual association area, also known as the secondary visual cortex, is accountable for providing context for the data supplied by V1.

The dorsal visual route, also known as the dorsal stream, is information sent by the primary visual cortex (V1) to areas V5 and V3A. These sections, respectively, discuss motion and form. Additionally, they communicate with the ventral visual pathway (just to add to the confusion), although they primarily send information to the parietal lobe’s visual areas. This suggests that the dorsal visual pathway would result in some motor activity, such as taking up an object. The parietal lobe is known to handle visual, navigational (proprioception), eye movement, and tactile information. As a result, the dorsal stream is also referred to as the where channel by scientists.

Memory and recognition are linked to the ventral visual circuit (the “what route”). Data from V1 is transferred to V2. V2 categorises information and sends it to regions V3 and V4 or the parietal lobe directly. There is speculation that V3 cells react to item position, although very few is learned regarding them. Visual region V4 may assist create forms and improve contrast between colours by determining how much attention is devoted to an item.

Information then travels to the temporal lobe, where it is combined with memories to build complex visuals. This is especially crucial when it comes to face recognition. Prosopagnosia is the inability to identify faces despite normal vision. This visual memory impairment is linked to injury to the temporal or occipital lobes.

Human Visual Development

Our cortical vision (brain visual perception) evolves throughout time. Babies have terrible vision. Vision accuracy (clearness), contrast, colour, shape, and movement awareness require months to reach optimal levels. Only binocular fusion (incorporating data from both eyes into a single sight), stereopsis (deep sensation), and stereo acuity (clearness of a single picture provided by both retinas) grow rapidly, but separately, between three months and three years of age. This suggests that if a cortical visual abnormality is treated early enough, it may be corrected before the visual cortices develop.

Surprisingly, our genes have less effect on our cortical vision than our surroundings. Despite the existence of good eye and brain tissues, a cruel experiment in which newborn kittens had one eye sewn shut resulted in permanent vision impairment. A kitten reared solely in the presence of horizontal lines will always be blind to vertical lines as it grows up to be a cat.

However, like with everything involving the brain, things aren’t always that straightforward. Due to brain plasticity, several cortically blind individuals with early V1 injuries have experienced a remarkable recovery of eyesight later in life, or the brain’s capacity to repair and reorganise after harm. A one-sided occipital lobe lesion that occurs during foetal development may not always culminate in one-sided cortical vision loss after birth.

Because embryos are recognised for their flexibility, the immature tissue of the opposing hemisphere’s occipital lobe may be able to operate on either side of the brain. The rare phenomenon known as blindsight, in which a blind individual may react to vision stimuli whereas both eyes are cortically blind, is another indicator of how complicated our cortical vision pathways are; this suggests that additional structures of the central nervous system are always in action. There is much more to learn.

Occipital Lobe Damage

Strokes, trauma, and brain tumours are the most common causes of occipital lobe injury. We might have heard about occipital neuralgia, as it is triggered by nerve injury at the neckline of the neck and is unrelated to the occipital lobe.

Even if other visual components are undamaged, early injury to the occipital lobe may result in lifelong cortical blindness. Hemianopsia is a loss of visual field to the left or right of the vertical centre of an image caused by unilateral (one-sided) occipital lobe lesions; a sort of left lesion creates contralateral (right-sided) hemianopsia, whereas a right-sided lesion generates contralateral (left-sided) hemianopsia. Homonymous hemianopsia is the loss of the identical area of the field of vision in each eye.

Occipital lobe epilepsy (OLE) is a kind of epilepsy that may affect up to 10% of people. It can be classified as idiopathic (of unknown origin) or symptomatic (with a lesion). Because both conditions induce the same sort of hallucinations, this kind of epilepsy may sometimes be confused with ocular migraines (observing spiky, glistening rainbows). OLE may also cause palinopsia (the repeated perception of an item no longer present in the field of vision), lights flashing, and transitory cortical vision loss.

People with occipital lobe epilepsy may encounter Anton syndrome. The individual who is afflicted is unaware that they are losing their eyesight and will believe visual hallucinations, events, and feelings to be authentic memories.

The Riddoch phenomenon, also known as statokinetic dissociation, happens when an individual can only detect moving items in a blind area; stationary objects are undetectable. One patient with Riddoch syndrome described becoming ready to see rain pouring down a glass but not seeing through it. Another mentioned seeing her daughter’s hair swaying but not being able to see her kid. Akinetopsia, or motion blindness, is the polar opposite of statokinetic dissociation. Static objects are visible while moving ones are not.

Color agnosia and cerebral achromatopsia are two different disorders that impact colour processing and the ability to distinguish and sense colour. Damage to the occipital lobe might also cause this.

References

• Rehman A, Al Khalili Y. (Updated 2019). “Neuroanatomy, Occipital Lobe.” Treasure Island (FL), StatPearls Publishing. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK544320/
• Moini J, Piran P. (2020). “Functional and Clinical Neuroanatomy: A Guide for Health Care Professionals.” London, Academic Press.
• Kaplan P W, Fisher R S. (2005). “Imitators of Epilepsy.” New York NY, Demos Medical Publishing.
• Martin T, Das A, Huxlin K. (2012). “Visual cortical activity reflects faster accumulation of information from cortically blind fields”. Brain, 135; 11, Nov 2012,  3440–3452. Retrieved from https://doi.org/10.1093/brain/aws272