Video: Brodmann areas

Gerardus Mercator maybe one of the most well-known cartographers to map the world onto a globe, but have you ever heard that the German anatomist, Korbinian Brodmann, was the pioneer of mapping the human brain? In the early twentieth century, he described the cerebral cortex according to its cytoarchitecture or its histological structure and organization. In doing so, he mapped the brain into fifty-two areas, which have since been correlated to various cortical functions.

From humble beginnings as a maidservant son and a schoolteacher who described him as weakly capable, Brodmann certainly exceeded expectations during his medical career. However, his research was interrupted by the first world war and cut short by his unexpected and sudden death. Who knows what else he might have discovered? Despite this, Brodmann made his mark in neuroanatomy, and in today's tutorial, we're going to talk about his legacy – the Brodmann areas.

So, let's begin our tutorial with a quick overview of what we're going to be talking about today. But, don't panic, I'm not going to take you through or expect you to know every single area – we'd be here all day. Instead, I'll discuss key Brodmann areas found in each lobe of the brain. So, today, we'll be looking at areas found in the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. Finally, we'll conclude our tutorial with some clinical notes.

Before we really dive into it, it's worth mentioning that Brodmann’s classification system is based on the fact that the human cerebral cortex is composed of six cellular layers namely, the molecular layer, the external granular layer, the pyramidal layer or the external pyramidal layer, the inner granular layer, the ganglionic layer or the inner pyramidal layer, and the multiform layer.

The histological structure and organization of these layers varies between areas. In other words, each Brodmann area is characterized by a particular arrangement of these layers and the cells which populate them. As we explore these areas, we won't be examining them in numerical order, rather according to the lobes of the brain in which they're arranged. So, without further ado, let's get started with the Brodmann areas found in the frontal lobe.

First, let's familiarize ourselves with the frontal lobe, which is the largest part of each cerebral hemisphere. It is separated from the parietal lobe by the central sulcus and from the temporal lobe by the lateral sulcus. Its functions include the control of voluntary movement. It's also involved in attention, short-term memory tasks, motivation, and planning.

Okay, now let's have a look at the key Brodmann areas found in the frontal lobe, starting with the Brodmann area 4, which is also known as the primary motor cortex. Brodmann area 4 is located in the precentral gyrus and controls voluntary movement. So, when you want to impress your friends with your dance moves, this is the area of the brain that you use. Here we can see the lateral surface of the brain, but this area also extends onto the medial surface of the hemisphere as we can see in our next image here.

Brodmann area 4 contains a somatotopically organized map of the contralateral side of the body, which is often represented using the motor homunculus. As you can see, the areas that carry out more complex or finely controlled movements such as the muscles of the face and hand are depicted larger which is representative of the amount of cerebral cortex associated with them. Areas such as the back, which are responsible for larger gross movement of the body, are reflected by the smaller area of the cerebral cortex dedicated to it.

Next, we're going to talk about Brodmann area 6, which contains the premotor cortex and the supplementary motor cortex, and is located immediately anterior to the primary motor cortex. This region is critical for the planning of voluntary movements. So, this is the area you use to plan exactly how you're gonna bust those moves. Again, we can see that this region extends onto the medial surface of each cerebral hemisphere.

Now we're looking at the area known as the frontal eye field, formed largely by Brodmann area 8 from a medial and lateral perspective. As the name suggests, this area plays a role in eye movement.

The next region we're going to talk about is part of the dorsolateral or anterior prefrontal cortex. So here we can see Brodmann area 9, which is involved in motor planning, organization, and regulation, sustaining attention, and working memory.

We're now looking at Brodmann area 10, which is in the cortex of the frontal pole and is involved in memory retrieval and executive functions such as decision-making.

The last two areas we’re going to look at are collectively known as Broca's area, which is named after the French physician, Paul Broca. Broca's area consists of Brodmann areas 44 and 45. This area is found in the frontal lobe of the dominant cerebral hemisphere and is involved in speech production, speech related gestures, and according to recent studies, it is also involved in language comprehension.

With the main areas of the frontal lobe covered, let's move on to the Brodmann areas found in the parietal lobe.

Here we can see the parietal lobe, which is separated from the frontal lobe by the central sulcus and from the occipital lobe by the parieto-occipital sulcus. Its main function is the integration and processing of sensory information from all over the body. The first three areas we're going to look at are collectively known as the primary somatosensory cortex.

The primary somatosensory cortex is located in the postcentral gyrus and consists of Brodmann areas 3, 1, and 2. This order simply relates to their location on the brain from anterior to posterior. This region is responsible for processing sensory information including touch, proprioception, nociception or pain, and temperature. When receptors detect one of these sensations, the information is sent to the thalamus and then to the primary somatosensory cortex. As we can see here, the primary somatosensory cortex extends onto the medial surface of the cerebral hemisphere. Brodmann areas 3, 1, and 2 also contain a somatotopically organized map of the contralateral side of the body which can be represented by what's known as the sensory homunculus. As you can see, the more sensitive areas of the body are depicted larger, meaning that the larger portion of the cortex is associated with them.

The next two areas we're going to talk about are part of the somatosensory association cortex. First, we have Brodmann area 5, which we can see here from a medial and lateral perspective. This region is involved in the perception of personal space and using spatial imagery in deductive reasoning.

Okay, let's move on to look at Brodmann area 7, which we can see here highlighted in green. This region is involved in visuomotor coordination such as when reaching to grasp an object. Next, we have broadband area 39, which is located in the angular gyrus. This region is involved in reading, sentence generation, and mathematics. Lastly, we have Brodmann area 40, which is located in the supramarginal gyrus. This area is involved in the perception and processing of language.

Now that we've looked at the parietal lobe, let's talk about the Brodmann areas in the occipital lobe. So, first, we're going to look at the location of the occipital lobe, which we can see highlighted here in green. The occipital lobe is separated from the parietal lobe by the parieto-occipital sulcus and is responsible for processing visual information from the contralateral eye.

Okay, now let's have a look at the key Brodmann areas found at the occipital lobe starting with area 17. It lies in the walls and floor of the posterior part of the calcarine sulcus. We can actually see area 17 better from a medial perspective of the brain. This area is also known as the primary visual cortex or V1. You will also find it referred to as the striate cortex due to the appearance of the white lines on its surface. The primary visual cortex processes visual stimuli. Specifically, it is involved in the detection of patterns and light intensity as well as color recognition.

Next, we have Brodmann area 18, which corresponds to the V2 visual area, and Brodmann area 19, which is mostly associated with the visual area V4. It is debated whether the visual area of V3 is located in area 18 or 19. Together, these areas are known as the secondary visual cortex.

The secondary visual cortex surrounds the primary visual cortex and receives afferent fibers from it. Its job is to relate the visual information received from the primary visual area to previously seen sizes, colors, and shapes, which allows an individual to interpret what they're seeing.

We have one last region left to tackle, so let's move on to the Brodmann areas found in the temporal lobe. So, here we have the temporal lobe, which is separated from the parietal and frontal lobes by the lateral sulcus. The temporal lobe is involved in processing auditory stimuli, the formation of long-term memories, the perception of smell, and language comprehension.

First, we have Brodmann area 22. In the dominant hemisphere, this contains Wernicke’s area, which is named after the German physician, Carl Wernicke, and is involved in language comprehension.

Next, we have Brodmann area 27, which we can say here from a medial perspective. This area is located in the piriform cortex and is involved in the perception of smell.

The next two areas we're going to talk about are Brodmann areas 35 and 36, which are found in the perirhinal cortex. These areas are involved in memory.

Okay, let's talk about Brodmann area 37, which includes the fusiform gyrus. This region is crucial for facial recognition.

The next area I'm going to talk about is known as the primary auditory cortex. The primary auditory cortex consists of Brodmann area 41, and is responsible for processing auditory information.

The secondary auditory cortex follows this, and consists of Brodmann area 42. This area is also responsible for processing auditory information.

The last area we're going to talk about is Brodmann area 43, which is also known as the primary gustatory cortex. This region is responsible for the perception of taste.

It's worth mentioning at this point that Brodmann’s mapping of the brain isn't without flaws. First of all, he did not account for the interindividual variability of the localization and size of the areas; therefore, probabilistic maps are required to counteract this variability between subjects.

Probabilistic maps quantified the variation between subjects when certain brain regions are activated. They do this by expressing each area in terms of how many subjects it was activated in. For example, in a study of fifty subjects, a value of fifty percent would mean that twenty-five subjects activated the respective brain region. Advances in imaging techniques have also shown that several of Brodmann’s areas could be further subdivided into smaller areas. Another limitation is the observer-dependent definition of borders of cortical areas. Again, advances in imaging are helping overcome this problem.

Okay, so now that we're familiar with the key Brodmann areas, let's get clinical.

In today's clinical notes, we are going to talk about aphasia, which is when a person has difficulty with their language or speech. Aphasia is usually caused by a stroke or brain injury, and therefore, usually has a sudden onset. We're going to talk about two types of aphasia today – Broca's aphasia and Wernicke’s aphasia.

Broca's aphasia is also known as expressive aphasia, and as the name suggests, individuals with this condition struggle with expressing themselves. It is caused by damage to Broca's area, which is made up of Brodmann areas 44 and 45. People with Broca's aphasia know what they want to say, but they struggle to find the words which can result in slow and halting speech. However, language comprehension is relatively preserved.

Whereas Wernicke’s aphasia, also known as receptive aphasia, involves difficulty understanding language. It is caused by damage to Wernicke’s area which is found in Brodmann area 22. These individuals can speak easily, but the words they use don't always make sense. They may also add a nonexistent word to their sentences and become confused when others don't understand them.

Speech and language therapy is the main mode of treatment for people with aphasia. This aims to restore some of the individual’s ability to communicate as well as providing alternative methods of communication if required. For example, patients may find they can communicate by singing instead of talking as it uses a different area of our brain.

Before we bring our tutorial to a close, let's quickly summarize what we learnt today.

We started with the key Brodmann areas found in the frontal lobe. We started with Brodmann area 4, which is known as the primary motor cortex and controls voluntary movement. Next, we looked at Brodmann area 6, which contains the premotor and supplementary motor cortex and is critical for planning voluntary movements. We then looked at Brodmann area 8, which is involved in eye movement, and next, we looked at Brodmann area 9, which is involved in motor planning, and Brodmann area 10, which is involved in decision-making. Lastly, we looked at Broca's area, which consists of Brodmann area 44 and Brodmann area 45 and is involved in speech production.

Our next mission was the Broadman areas found in the parietal lobe. Firstly, we looked at the primary somatosensory cortex, which consists of Brodmann area 3, Brodmann area 1, and Brodmann area 2. This region is responsible for processing sensory information. Next, we saw Brodmann area 5 and Brodmann area 7, which are part of the somatosensory association cortex. We then looked at Brodmann area 39, which is involved in reading and mathematics, and lastly, we looked at Brodmann area 40, which is involved in the perception and processing of language.

We then looked at the three areas in the occipital lobe. We looked at Brodmann area 17, which known as the primary visual cortex and processes visual information. Then we saw Brodmann areas 18 and 19, collectively known as the secondary visual cortex. These last two regions are involved in the interpretation of visual information.

Finally, we looked at the key Brodmann areas found in the temporal lobe. First, we looked at Brodmann area 22. This region contains Wernicke’s area and is involved in language comprehension. Next, we saw Brodmann area 27, which is involved in the perception of smell followed by Brodmann area 35 and Brodmann area 36, which are involved in memory. We then saw Brodmann area 37, which is involved in facial recognition. The next two areas we saw, Brodmann areas 41 and 42, are known as the primary auditory cortex and secondary auditory cortex respectively. The last area we looked at was Brodmann area 43, which is responsible for the perception of taste.

Once we'd covered all the Brodmann areas, we then discussed aphasia in our clinical notes.

So that brings us to the end of our tutorial on the Brodmann areas. Hope you enjoyed it, thanks for watching, and happy studying!