The description and measurement of circadian rhythms.
- Describe the standard method used for the recording and graphing of behavioral rhythms in animals, especially the use of double-plotted graphs, where the abscissa scale is 48 hours long.
- Define the general terminology used to describe rhythms, including: circadian, period (tau), phase, phase relationship, nadir, acrophase.
- Describe how light-dark cycles are manipulated in experiments, and become familiar with the abbreviations used to represent artificial and natural light-dark cycles.
- Contrast entrained and free-running biological rhythms.
- Understand that light has been the most reliable zeitgeber, or "time-giver" to life on the planet earth.
An actograph is a graphical representation of sleep/wake patterns. The darkened bars are the times of activity. The clear areas are the times of inactivity. When viewing an actograph, you should view the X and Y axis. The X axis is also called the abscissa. If the actograph is single-plotted, there are 24 hours on the x-axis. If the actograph is double-plotted, there are 48 hours on the X-axis. The Y axis tells the number of days or hours that the data was collected. Looking at the graph, you can tell if the organism has an endogenous clock of less than 24 hour or more than 24 hours. If the graph slants from right to left, there are less than 24 hours in the organism's activity. If the graph slants from left to right, there are more than 24 hours in the organism's activity.
Assignment
Three actographs (look closely to see the labels A, B, and C). Assume that the abscissa is either 24 or 48 hours for each actograph. You are asked to write two sentences for each actograph.
First, write a single-sentence description of the actograph, without using any of the special vocabulary you just learned; state what is going on in terms that dear old Mom would understand if you were talking to her on the phone.
Second, write a more technical sentence for each in which you provide a rough estimation of tau (the duration of the period), your understanding or best guess of the labels for the X- and Y-axes, and a statement as to whether each actograph is single- or double-plotted.
Reminder: Your completed assignment will have a total of SIX sentences, two that start out with the words, "In actograph A . . ." etc. Since two of the actographs don't include numerical axes, you will have to make some guesses to complete this assignment.