An example of oscillations in the size of the pupils of a urethane-anaesthetised rat.

<p>Top: frames of the left and right eyes taken at different recording times. Dotted ellipses indicate detected edges of the pupils, and the corresponding area of the pupil is given in the bottom right corner of each frame. Bottom: graphs showing the oscillatory changes of the areas of pupils observed simultaneously in the left (red line) and right (blue line) eyes. Both graphs have the same time scale. Dotted lines with arrows indicate the exact times at which the frames shown in the top were taken.