Occipital Lobe: Anatomy, Characteristics And Functions
The cerebral cortex, which is the most iconic part of the brain and known for its folds and labyrinth-like shape, is not an organ in charge of performing a specific function. What happens, rather, is that different parts of the cerebral cortex are responsible for participating in different mental processes although all of them work in coordination with each other.
For example, him occipital lobe located in the part of the brain closest to the back of the neck, is very different from the frontal lobe (located in the part of the brain closest to the forehead) not only because of its shape and location, but especially because of the functions of which These two lobes of the brain are in charge.
If the frontal lobe has a very important role in executive functions and the initiation of deliberate actions, the occipital lobe has a very specific role that has to do with perception and, specifically, with the recognition and analysis of everything we see. Next we will see the main characteristics of this last part of the brain.
The occipital lobe is one of the smallest brain lobes and occupies a small portion of the back of the brain, between the cerebellum, the temporal lobe and the parietal lobe.
Furthermore, as with the rest of the lobes, it exists in both the left and right cerebral hemispheres, which means that each person has two almost symmetrical occipital lobes that are separated by a narrow fissure.
Unlike what happens with the frontal lobe, it is believed that throughout the evolution of the ancestors of our species the occipital lobe has not grown in proportion to the rest of the parts of the brain. That is to say, while the rest of the areas of the cerebral cortex were developing and organizing in a more complex way, the occipital lobe has remained almost the same over hundreds of thousands of years; Although, curiously, it is believed that in Neanderthals, who were an evolutionary branch parallel to that of Homo sapiens, this area was larger (relative and absolute) than that of our species.
However… What is the occipital lobe responsible for and why has it not been growing throughout our evolutionary history? Although there is no area of the brain that has only one function, since all of them work together and in a coordinated manner, the process that best defines the usefulness of the occipital lobe is the processing of visual information.
The occipital lobe includes the visual cortex, which is the area of the cerebral cortex where information from the retinas reaches first. In turn, the visual cortex is divided into several regions classified according to the level of processing they are responsible for.
Thus, the primary visual cortex (v1) is the part of the occipital lobe that processes the most “raw” visual data and is responsible for detecting the general patterns that can be found in the information collected by the eyes. These general and not very detailed data about what is seen are sent to other parts of the occipital lobe in charge of carrying out more refined processing of vision and these, in turn, send the analyzed information to other areas of the brain.
The dorsal route and the lateral route
Once the information has passed through the primary visual cortex in the occipital lobe**, the stream of data emitted by this area bifurcates following two different routes: the ventral route and the dorsal route**. These extend in parallel while communicating with parts of the brain that the other pathway does not directly access, as we will see.
ventral route
The ventral pathway starts from the primary visual cortex in the occipital lobe and goes to the frontal area of the brain through the lower part of the brain, which includes the visual cortices V2 and V4 which, as indicated by their number, They are responsible for processing the information already processed by v1
It is considered that the neurons that participate in this “assembly chain” of visual information They are responsible for processing the characteristics of the isolated elements that are being seen at all times, that is, about the content of the vision. Therefore, this route is also called the “what” route.
Dorsal route
This route goes from the occipital lobe to the frontal area of the cerebral cortex through networks of neurons near the top of the skull. In it, the information processed by the primary visual cortex reaches the parietal lobe through the visual cortices v3 and v5. This visual processing area is believed to is responsible for establishing the characteristics of the location and movement of what is seen ; That is why the dorsal pathway is also called the “where and how” pathway.
Together with the ventral pathway, this visual processing route related to the occipital lobe tells us about how the brain works: sometimes, mental processes that seem to form a unit and that reach our consciousness as a complete experience, are actually the product of several brain pathways that work in parallel, each one focused on a different aspect.
The occipital lobe and epilepsy
It is believed that the occipital lobe plays a prominent role in the occurrence of epileptic seizures, or at least in part of them. These are cases in which exposure to frequent “flashes” of intense light causes the appearance of a pattern of electrical signal emission by neurons in the occipital lobe that extends throughout the brain, causing the attack.
Due to the complexity of the functioning of the brain and the speed with which the neurons work, not much is known about the mechanisms by which this type of epileptic attacks appear, although from these cases it is assumed that some external stimuli can cause it to appear. a focus of epilepsy in some part of the temporal lobes, which begins to affect other parts of the brain in the same way that the visual cortex sends information to other regions under normal conditions.
However, For these cases to occur, it is believed that there must be a biological or genetic propensity
In conclusion
Although processing the data collected by the retinas is probably not the only function of the occipital lobe, It is practically occupied by the visual cortex and that is why it is believed that its main function has to do with the interaction of the information that arrives from the optic nerves
It may seem strange that a single sense claims for itself an entire lobe of each cerebral hemisphere, but it is not so strange if we take into account that the temporal lobe is the smallest in human beings and that in mammals the processing of the information collected through the eyes it usually occupies very large areas of the brain. Ultimately, as descendants of an arboreal and diurnal evolutionary line, vision has been very important both when moving through three-dimensional spaces full of dangers and obstacles and when detecting predators and food.
On the other hand, another of the most important aspects of the occipital lobe is that it is the beginning of the two parallel information processing pathways. This gives us a better understanding of what the perceptual phenomenon of vision is like which is presented through at least two separate chains of information processing: on the one hand the dorsal pathway, responsible for allowing us to know well the movement, position and location of what we see, and on the other the ventral pathway, related to the recognition of what we are seeing (that is, the integration of small image fragments into large units that we can identify).
