As we mentioned in the previous lesson, sensory stems tend to be organized as maps in the brain that represent the physical world in some organized manner. One of the clearest example of this is in the somatosensory, or touch, system. Touch information originates in a series of receptors sensitive to pressure in the skin, which then proceeds to the spinal chord and ultimately to the somatosensory cortex via the thalamus. In the somatosensory cortex we have an orderly representation of different regions of our skin, so for example touch sensation originating from nearby locations in your forearm will project to nearby neurons in the somatosensory cortex. However, not all regions of the skin are represented equally in the cortex. Areas which have greater touch sensitivity and acuity, such as the palms of your hands or your tongue, will occupy a relatively larger portion of the somatosensory cortex than for example your torso. This is because your skin on your fingers and lips has a much higher number of skin receptors than the skin on your back. As a result, the map will look greatly distorted. Sort of like this:
This distorted map of your skin on the brain is sometimes referred to you as a homunculus (latin for “little man”). Here’s what a homunculus would look like if the brain representations scaled matched up with body size:
Pretty weird, no? In this exercise you will build a homunculus of yourself by first testing the sensitivity of your skin in different parts of your body using a two-point discrimination task.
1. Gather some cardboard, a bunch of toothpicks, sticky tape, and a ruler and find a friend to help you.
2. You will map the acuity of the skin. Follow the instructions on this link to complete the task.
Note: You don’t need a data collector, just have your helper write down the data on a piece of paper.
3. Once you have collected the data, it’s time to go to the “Homunculus Mapper”!
4. Click on an avatar that most resembles you (or resembles what you’d like to look like), enter your name.
5. Then, enter the data for each body part in the drop down menus. Notice that the size of each body part changes relative to acuity, that is the finer your touch discrimination is, the larger that part of the body becomes.
6. Use your computer to take a screen shot or create a PDF file of your homunculus, including the data.
Note: Click here for help taking a screenshot on a Mac or PC.
7. After you have taken your screenshot choose one of the following 2 options for uploading and reflecting upon your work. Ideally, we would like all of your work as one document.
1. Download the following worksheet: Homunculus.doc
2. Save the worksheet on your computer and rename it: LastName.FirstName.Homunculus.doc
3. Insert your screenshot and answer the questions in the document.
Note: To add images (.jpg, .png, .tiff, etc.) to a Word document, click 'Insert' and choose photo. For more detailed instructions from Microsoft, click here.
4. Click 'Submit Assignment' and upload your completed worksheet on this assignment page.
1. Open 'Google Docs'. (You must have a google account first. To set up a Google account, click here.)
2. Create a new 'Document'.
3. Click here and then cut and paste the assignment questions into your new Google doc. and enter your answers.
Note: To add images (.jpg, .png, .tiff) to a Google document, click 'Insert' and choose photo. For more detailed instructions from Google, click here.
4. When you are finished with your work, use the 'File' menu to rename the document as LastName.FirstName.Homunculus and download it as a .pdf.
5. Click 'Submit Assignment' and upload your completed worksheet on this assignment page as .pdf.