1. CELL COMMUNICATION Activity developed during the 2009 Exploratorium Summer Institute “Class Menagerie” by: Caltech Fellow Xoana Troncoso and High School Teachers Patricia Dunlap, Robert Martin & Erick Roldan

2. Background While driving in our cars, if we would like to know how fast we are going, we have the luxury of simply looking at the speedometer. There are clocks and calendars for time, thermometers for temperature, and scales to tell us exactly how much mass an object has. We live in a world of absolutes! However at the cellular level things are not so convenient. Our cells don’t have the luxury of using tools as measuring devices, but they do have one very powerful resource: each other! All of our cells are in constant communication with each other; imagine a party where everyone is talking to everyone at the same time. Specialized cells in our brains called neurons communicate by firing electrical signals called action potentials. People have even discovered ways to listen in on these electrical conversations. What scientists have discovered is that these specialized cells are only able to interpret data by constantly comparing values to each other. For example, the only way that your brain can tell that a piece of paper is white, is by having white sensing neurons and dark sensing neurons have an electrical conversation in which they compare their values.

3. UP - DOWN Play the FALLS_loop.mov movie

4. What’s going on???

5. No movement Rested neurons Downward movement Rested neurons No movement Tired DOWN neurons No movement Rested neurons =>= DOWN neurons UP neurons Compare UP &DOWN We see… NO movement DOWN movement < UP movement!! NO movement

6. Expansion - Contraction

8. No movement Rested neurons Contraction Rested neurons No movement Tired CONTRACT neurons No movement Rested neurons =>= CONTRACT neurons EXPAND neurons Compare CONTRACT & EXPAND We see… NO movement CONTRACTION < EXPANSION!! NO movement

9. BRIGHT - DARK

10. Gray Rested neurons Bright Rested neurons Gray Tired DARK neurons Gray Rested neurons =>= DARK neurons BRIGHT neurons Compare BRIGHT & DARK We see… GRAYDARK < BRIGHTGRAY

11. COLOR

12. Which colors does the brain compare? When the image is… Red Blue Green Yellow the after image is… Greenish Yellowish Reddish Bluish

13. RED Rested neurons BLANK Tired RED neurons BLANK Rested neurons >= RED neurons GREEN neurons Compare RED & GREEN We see… RED < GREEN!!BLANK

15. Try your to design your own afterimage!

16. CELL COMMUNICATION Activity developed during the 2009 Exploratorium Summer Institute “Class Menagerie” by: Caltech Fellow Xoana Troncoso and High School Teachers Patricia Dunlap, Robert Martin & Erick Roldan