The cerebral cortex, which is the most iconic part of the brain and known for its folds and maze shape, is not an organ that performs a specific function. What happens, rather, is that different parts of the cerebral cortex are in charge of participating in different mental processes , although they all work in coordination with each other.

For example, the occipital lobe , located in the part of the brain closest to the back of the head, is very different from the frontal lobe (located in the part of the brain closest to the forehead) not only in its shape and location and form, but especially in the functions that these two lobes of the brain perform.

If the frontal 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.

What is the occipital lobe?

The occipital lobe is one of the smallest cerebral lobes , and occupies a small portion of the back of the brain, between the cerebellum, the temporal lobe and the parietal lobe.

In addition, as with the other 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 the frontal lobe, the occipital lobe is thought not to have grown in proportion to the rest of the brain throughout the evolution of our species’ ancestors. In other words, while the rest of the areas of the cerebral cortex were developing and organizing themselves in a more complex way, the occipital lobe has remained almost the same throughout hundreds of thousands of years; although, curiously, it is believed that in the Neanderthals, which were an evolutionary branch parallel to that of Homo sapiens, this area was larger (relative and absolute) than that of our species.

Functions of this brain region

Now… What does the occipital lobe do and why has it not been growing throughout our evolutionary history? While no area of the brain has only one function, since all of them work together in a coordinated way, the process that best defines the usefulness of the occipital lobe is the processing of visual information.

The occipital lobe comprises the visual cortex, which is the area of the cerebral cortex where information from the retinas first arrives. The visual cortex is in turn 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 in charge of detecting the general patterns that can be found in the information collected by the eyes. This general, undetailed data about what is seen is sent to other parts of the occipital lobe for further processing of the vision and these, in turn, send the analyzed information to other areas of the brain.

The dorsal and the lateral route

Once the information has passed through the primary visual cortex in the occipital lobe , the stream of data that this area emits forks into two different routes: the ventral route and the dorsal route . These routes extend in parallel while communicating with parts of the brain that the other route does not directly access, as we will see.

Ventral line

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 it, which includes the visual cortexes V2 and V4 that, as their number indicates, are in charge of processing the information already worked on by v1 .

It is considered that the neurons that participate in this “assembly line” of visual information are in charge of processing the characteristics of the isolated elements that are being seen at each moment , that is, about the content of vision. That’s why 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 v3 and v5 visual cortexes. This visual processing zone is believed to be 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.

Along with the ventral pathway, this occipital lobe-related visual processing pathway tells us about how the brain works: sometimes, mental processes that seem to form a unit and come into our consciousness as a complete experience are actually the product of several brain pathways working in parallel, each focused on a different aspect.

The Occipital Lobe and Epilepsy

The occipital lobe is believed to play a major 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 a pattern of emission of electrical signals by neurons in the occipital lobe that spreads throughout the brain causing the seizure.

Due to the complexity of the brain’s functioning and the speed with which the neurons work, not much is known about the mechanisms by which this type of epileptic seizure occurs, although it is assumed that some external stimuli can cause a focus of epilepsy to appear in some part of the temporal lobes, which then affects 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 a biological or genetic propensity must exist .

By way of conclusion

Although the processing of the data collected by the retinas is probably not the only function of the occipital lobe, is practically occupied by the visual cortex , and therefore its main function is thought to be related to the interaction of the information coming from the optical nerves .

It may seem strange that a single sense claims for itself an entire lobe of each brain hemisphere, but it is not so strange if we consider that the temporal lobe is the smallest in humans and that in mammals the processing of information collected by the eyes usually occupies very large areas of the brain. After all, as descendants of a diurnal and arboreal evolutionary line, vision has been very important both in moving through three-dimensional spaces full of dangers and obstacles and in 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 paths of information processing. This gives us a better understanding of the perceptive phenomenon of vision , which is presented through at least two separate information processing chains: on the one hand the dorsal pathway, which allows us to know the movement, position and location of what we see, and on the other the ventral pathway, which is related to the recognition of what we are seeing (i.e. the integration of small image fragments into large units that we can identify).

Bibliographic references:

  • Carlson, Neil R. (2007). Psychology : the science of behaviour. New Jersey, USA: Pearson Education.
  • Destina Yalçin, A.; Kaymaz, A.; Forta, H. (2000). “Reflex occipital lobe epilepsy”. Seizure.
  • Houdé, O. Mazoyer, B., Tzourio-Mazoyet, N. (2002). Cerveau et psychologie Introduction à l’imagerie cérébrale anatomique et fonctionnelle.
  • Schacter, D. L., Gilbert, D. L. & Wegner, D. M. (2009). Psychology. (2nd ed.). New Work (NY): Worth Publishers.