The little man from Wikimedia Commons 

This journey will meet “Two little humans” who “live” on the brain surface. Dr. Wilder Penfield and Edwin Boldrey “discovered” them in 1937.

That is an amazing story.

They began their expedition while working at McGill University. Dr. Wilder Penfield served there as a brain surgeon. During that time, while operating under local anesthesia, they mapped corresponding brain regions where the sensory information are received from different body parts. They also succeeded in demonstrating the corresponding brain regions which send signals to move relevant body parts.

Together with Edwin Boldrey, he published their story in the “Brain” journal writing a 50-page long article with drawings.

“Two little humans” (Figure 1) – now famously called “Homunculus of the brain” – lie along the Central sulcus which separates the Frontal lobe from the Parietal and Temporal lobes.

Homunculus in the brain

Figures 2 and 3 depict the two little humans who lie along the Central sulcus – a groove that separates the Frontal lobe from the Parietal lobe (You can read this on the Journeys to the brain -2: A walk over the brain surface).

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As you can see in Figure 4 (below), the upper inside surface area controls our foot and legs. Let us start from Figure 2. When we begin to climb, we will step on the areas that receive information from and send commands to the facial structures. Further up, we will find areas that receive information and send commands to arms, body, legs, and feet. It follows a highly organized distinct pattern. And, the more complex the job is, the larger the designated area.

This information is very useful for carers because most of the time, these are the body parts affected due to stroke You can read about the brain’s blood supply by joining me on another journey.   

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(Image source: University of Utah); creative commons license

Prelude to brain surface: Journeys to the brain -2: I extracted and cropped several visuals for this post about the brain surface from a video clip produced by the University of Utah under the Creative Commons license. The presenter who appears in the original clip was Dr. Suzanne S. Stensaas, Ph.D., Professor Emeritus at that University. I am greatly indebted to Dr. Suzanne S. Stensass, and her team for making this valuable resource. I cited the link at the end of this post for the benefit of anyone interested in watching the full video.  

Please note that this post contains several visuals of an unfixed and fixed brain specimens. 

We began this series with the journey to the brain covers.

This post journeys on the brain surface. The brain surface is full of ridges (bumps) and valleys (grooves) (see Figure 1). (The folded one is the outer covering; however, its inner coverings are still intact in this figure). Experts have given specific names to recognize these bumps and grooves. Moreover, in the medical field, the bumps are named as gyri (its singular word is gyrus) and grooves as sulci (its singular word is sulcus).

The purpose of these ridges and valleys is to increase its surface area. As a result, the surface areas that are assigned to specific jobs have enough space for their work.

Now, we will see the bird’s eye view of the brain.

Naming the brain regions

Experts have classified different regions of the brain; they call it lobes: frontal lobe, parietal lobe, temporal lobe, and occipital lobe. This naming depends on the region it places within the skull. Interestingly, those job functions are distinct to those lobes. Figure 2 shows those four lobes on the left side. Similarly, we have the same mirror lobes on the right side too.

Demarcations of the lobes

As shown in Figure 2, the Central groove (Sulcus) separates the Frontal lobe from the Parietal lobe. Moreover, another groove that sits between the Parietal lobe and the Occipital lobe separates those two lobes. Similarly, a large groove which is called Lateral fissure separates the Parietal lobe from the Temporal lobe.

Brain regions (lobes) in detail:

This is a re-visit to the brain surface. I am using another set of visuals of a fixed brain specimen from a different video clip from the same team. In this visit, I peep into a one lobe at a time. You can view the full video clip via this link (number 11 – Cortical localization): https://library.med.utah.edu/neurologicexam/html/brain-dissections.html#10 

Frontal lobe

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With Figure 3, I am starting my walk from the front end of the Frontal lobe. Dr. Suzanne is holding the under-surface of the Frontal lobe with her index and middle fingers of both hands. From that on-wards, when I climb to the top, I meet the Central groove (sulcus). That is where the both index fingers are placed in Figure 4.

We – humans – own the largest Frontal lobe proportionate to the body size among all animals. This lobe carries out jobs that no other animal can do: higher jobs such as thinking, speaking, and decision making jobs. However, every single area of this lobe is specialized for one job. If something happens to this area, we lose that function. For example, if a stroke attack prevents blood supply to Broca’s area, which is specialized in speech production, we lose speech.

Parietal lobe

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As soon as I jump over the Central groove from the Frontal lobe’s edge to the other side, I land on to the Parietal lobe. It lays behind the Frontal lob. The metal pointer in Figure 6 lies on the Central groove. The Parietal lobe extends back until it meets the next lobe – The occipital lobe.

We can see the upper-left side view of the left Parietal lobe in Figure 7. In this visual, the metal pointer shows us the side view of the Central groove. The parietal lobe reads messages related to taste, touch, and temperature and controls our balance while standing and walking. This simply means if this area inflicts any damage, we will not be able to taste, feel touch, or temperature and will fall.

Temporal lobe

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Now, walk with me over to the brain’s left side through Figures 8 ans 9. In Figure 9, I meet a larger groove, in fact, a fissure; this is called Lateral Fissure.

Once I cross over this fissure, I meet the Temporal lobe. The part above is the side view of the left Frontal lobe.

The Temporal lobe’s main job is to understand and interpret the language. 

Occipital  Lobe

Behind the parietal and Temporal lobes, we find the Occipital lobe. The metal pointer in Figure 10 is in this region. The lobe spreads over the back of the brain. Without this area, we cannot see, recognize, and interpret anything although we have eyes.

In our next journey, we will meet the “two little humanoids” who live on our brain surface.

The information source: I extracted and cropped above stills from a video presentation presented by Dr Suzanne S. Stensaas, PhD, Professor Emeritus in the Department of Neurobiology and Anatomy of the University of Utah School of Medicine in 2012. I have no formal affiliation with the University. However, I found this valuable resource which is licensed under Creative Commons Non- Commercial use. 
As per the Creative Commons regulations, I am giving due prominence to the resource and its link for the readers to gain more knowledge of the topics I cover in this website.  
The website details are as follows: 
Neuroanatomy Video Lab: Brain Dissections by Suzanne S. Stensaas, PhD, Professor Emeritus
Department of Neurobiology and Anatomy
University of Utah School of Medicine.

link – number 11- Cortical localization: https://library.med.utah.edu/neurologicexam/html/brain-dissections.html#10: