egrees Celsius. A third theory, ecological hypothesis of foraging and predator avoidance, states that the lack of movement during sleep prevents animals from attracting the attention of predators (Sleep Syllabus).
             Generally, three measures have been used to define sleep and the different stages. The first is the electroencephalogram, abbreviated EEG, which measures brain waves. The brain waves are measured by electrodes, placed on the scalp, that measure small changes in voltage. These voltage changes are powerfully amplified and examined for variations in duration and amplitude. The second measure is called the electrooculogram, abbreviated EOG, which records eye movements. The eyeball acts as a small battery, and so an electrode placed on the skin records changes in voltage as the eye rotates. The third measure is c
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