Sensation and movement of different parts of the body are controlled by different areas of the brain. For instance, when you move your index finger, a specific area on the top of your brain triggers a signal that tells the muscles on your index finger to move.  When you touch something with your index finger, a neighboring area of your brain receives a signal about that touch sensation. 

Look at your hand.  Now look at your arm.  Which is bigger?  Your arm, right?  Does that mean your arm has larger area of  the brain devoted to its control? Actually, no.   Sensations and movements of your hand are controlled by more of your brain than sensations and movements of your arm.  This larger area allows you to make finer movements and a have better sense of touch.

The area of your brain devoted to each body part is represented in the homunculus by how large each body part is.  Looking at the illustration above, it should now make sense to you why the lips and tongue are so large and the knee is so small. Your lips and tongue are specialized for making small, precisely controlled movements (like when you speak), whereas your knee makes larger, less precise movements. Make sense? 

Materials:

1. Bike helmet
   

2. Latex gloves (one pair)
   

3. Masking tape
   

4. Newspaper
   

5. Paint
   

6. Paint brush
   

7. Papier-mâché paste

If you visually “map” body parts to the areas of the brain that control them, you end up with the illustration to the right.  This visual representation of the brain’s map is called a homunculus, Latin for little man.

More about the homunculus

University of Washington, Seattle

Make one with your class

Human brains have many valleys and ridges called sulci and gyri, respectively.  To recreate this impression of brain anatomy, you can make a papier-mâché model of the brain on a bicycle helmet.

The shape of the brain and body parts are molded using pieces of rolled up newspaper, which are held together with masking tape.

To make a solid structure and to smoothen the surface, strips of newspaper are wetted with paste and layered on every surface of the mold.

Many brain cells control sensation and movement of the lips so make a big lip for the homunculus. Technically, brain cells that control the tongue are found below the area that represents the lip, but to make the tongue easy to identify, we stuck it in between upper and lower lips. Some parts of the body, such as the feet, legs and arms, are omitted to make our model simple.

Let the paste completely dry before the applying the next layer.  Add multiple layers over several days to reinforce the structure.

When the last layer is dry paint the surface.

We debuted our homunculus hat at the 2007 Society for Neuroscience (SfN) Annual Meeting in San Diego and since then, it’s attracted a lot of attention.