Tick Tock, Tick Tock, Does Your Mouse Know the Time on the Clock?
AbstractMice, rats, and other rodents are typically nocturnal animals; that is, their activity level is highest at night. For this science fair project, you will build a device that records your pet's activity by monitoring movement of its exercise wheel to see how it varies during the day and night. You can also experiment with various ways of changing your pet's cycle of activity; for example, by playing with it during the day when it's normally resting.
The objective of this science fair project is to study how the activity level of your pet rodent varies over the course of a day-night cycle, and what factors affect this activity level.
David Whyte, PhD, Science Buddies
Thanks to Sandra Slutz, PhD, for suggesting this project idea.
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Cycles of biological activity that vary over the course of a 24-hour period are called circadian (the word comes from circa, which means approximately, and dia, which means day). The circadian rhythm is tied to the outside world, such as daytime and nighttime, but it is also dependent on an internal clock. This internal clock needs to be "reset" when the external signals change. For example, when you travel to a region in a different time zone, your internal clock needs to adjust to the new day-night cycles. In addition to the sleep-activity cycle, there are numerous other processes that follow a circadian rhythm. Figure 1 shows the timing of various circadian cycles in humans.
Figure 1. This diagram depicts some of the circadian patterns that occur in humans. Note that the clock is on a 24-hour cycle, so that 3:30 PM, for example, is noted as 15:30. The hormone melatonin, which is a key regulator of the internal circadian clock, peaks in concentration at 21:00 (9:00 PM). (Wikipedia, 2008).
Rodents are typically nocturnal, resting during the day and becoming active at night. In the wild, nocturnal activity helps the animal avoid predators. For rodents living in a desert environment, nocturnal activity also has the advantage of restricting activity to the cooler part of the day.
Animals actually have a number of internal clocks that are critical for normal functioning. The internal clocks are "set" by environmental cues, such as the day-night cycle, but they will continue to run even when the animal is kept in total darkness.
The objective of this science fair project is to study how the activity level of your pet rodent varies over the course of a day-night cycle. You will build a device that measures your rodent's activity by tracking the motion of your pet's exercise wheel. You can also experiment with factors that alter the normal day-night cycle of activity, such as keeping your pet awake during the day by playing with it.
Terms and Concepts
- Circadian rhythm
- Internal clock
- Nocturnal activity
- At what time of day is your pet rodent most active?
- When your pet rodent is active, is it for short bursts of a few minutes, or is it extended over a longer period of time?
- How quickly does your pet rodent's daily activity schedule adjust to changes in its environment?
- Wikipedia Contributors. (2008, August 3). Circadian Rhythm. Wikipedia: The Free Encyclopedia. Retrieved August 3, 2008 from http://en.wikipedia.org/w/index.php?title=Circadian_rhythm&oldid=229637148
For a history of the science of circadian rhythms and a glossary of terms, see this website:
Harmer, T. (2008, June). Introduction to Chronobiology. Retrieved June 9, 2008 from http://www.sbms.mvm.ed.ac.uk/bmto/neuroscience/NeuroSci4/harmar/Chrono1a.pdf
This site at the University of Utah has a good introduction to the genetics of mammalian internal clocks.
Siegel, L.J. (2008). The Time of Our Lives. Retrieved June 9, 2008 from http://learn.genetics.utah.edu/content/begin/dna/clockgenes/
The Howard Hughes Medical Institute has a number of animations about the fundamental biology of circadian rhythm:
Howard Hughes Medical Institute. (2008). Biological Clocks: Animations. Retrieved June 9, 2008 from http://www.hhmi.org/biointeractive/clocks/animations.html
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Materials and Equipment
- You should already own a mouse, a rat, a guinea pig, or a hamster, and know how to take care of it. Or you can study a pet rodent at your school.
- A rodent exercise wheel; the "Silent Spinner," available at most pet supply stores, works well because it turns smoothly with minimal wobble. But you can probably use the exercise wheel you currently own.
- An electronic bicycle speedometer; it should have a magnet that attaches to the wheel, and a sensor that counts the magnet's revolutions; you can purchase this at most sports stores or online.
- Clear adhesive tape or modeling clay
- Lab notebook
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To study circadian rhythms in your pet rodent, you will need to devote some time every day for several weeks to observing its activity levels. Your pet's response to changes in the environment, such as varying the amount of playtime your pet experiences during the day, may take several days to observe. Plan your experiments carefully, take thorough notes, and give yourself plenty of time for observation. And, of course, be sure not to cause any stress to your pet during the experiments.
- To start this science fair project, you should have access to a pet rodent that you are comfortable working with, either at home or at your school.
- Observe the pet during the day and record its activity levels. Check on it every 2 hours and watch it for 10-minute periods. If you aren't able to check on it that often, see step 3.
To measure the activity level when you are not present, install a bicycle speedometer on the pet rodent's exercise wheel.
- Read the instructions so that you know how to determine the distance traveled.
- The speedometer has a magnet that rotates with the wheel, and a sensor that counts the revolutions each time the magnet passes by.
- Tape or glue the magnet to the wheel.
- Attach the sensor to the wheel so that it records the magnet's movement. You can use clear adhesive tape or modeling clay to hold the sensor in place.
- The magnet needs to pass fairly close to the sensor for the speedometer to work.
Check the speedometer readings in the morning and in the evening for total distance travelled. If possible, check more often (every few hours) to determine the times of peak activity. Reset the speedometer between readings.
- If you want to record the actual distance, you will need to account for the size of the exercise wheel vs. the bicycle wheel. For example, if the speedometer is set to work with a wheel with a diameter of 26 inches, and the exercise wheel is 6.5 inches in diameter, then dividing the distance by 4 (that is, 26 inches/6.5 inches) will yield corrected results for distance traveled.
- To measure the relative activity levels, you can use the numbers on the speedometer without converting.
- The initial goal is to determine your pet's "baseline" activity level; that is, its daily activity level prior to any experimental changes in its environment. Observe your pet for several days to establish its baseline behavior and record the results in your lab notebook.
After several days, try increasing or decreasing the amount of time you are playing with your pet during the day. Record the time you spend playing each day. How does the amount of playtime you have with your pet during the day affect its nocturnal activity cycle?
- Note: Remember to change only one variable at a time. For example, to study how the length of playtime your pet has affects its activity level, first determine its "normal" baseline level of activity over the course of 24 hours, then change only the amount of playtime. Try to keep everything else in the pet's environment the same so that any changes you observe are due to the variable (playtime) that you control.
- How long does it take for your pet to change its activity cycle after you alter its playtime during the day? When you return your pet to its "normal" schedule, how long does it take for your pet to return to its "baseline" activity schedule?
- You might plan your experiments to last about one week each. For example, you could have a 3-day period of increased daytime activity, followed by a 4-day recovery period in which you return to your normal baseline activity.
- Repeat your experiments at least three times.
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- Change the pattern of light and darkness in your pet's cage. For example, what happens if you shorten the number of hours of light that the pet experiences? Remember not to stress your pet in any way, and keep your playtime and other variables constant.
- Many schools have classroom pets: a rat, rabbit, hamster, fish, or frog. If your class has a pet, study its behavior to see if you can determine any circadian rhythm patterns.
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