The Idea of an Essay, Volume 2

144 fifth stage as REM, or dream sleep. Within each progression through this pattern, various factors mark the transition from one stage to the next. Stages one and two, for instance, represent the initial, shallow levels of sleep; stages three and four enter a much deeper level; and REM involves the intermittent, shallow, and highly active levels. In more detail, the first stage one enters involves a period of light sleep from which he or she awakens easily. During this approximately five-minute stage, EEG studies revealed changes in the brain waves as they transitioned from alpha waves to theta waves (Epstein and Mardon 13-14). The units for such measurements are cycles per second. This designation refers to the frequency with which waves in the EEG recordings appear. Smaller waves of greater frequency and smaller amplitude (height) represent higher levels of brain activity, whereas larger waves of lower frequency and larger amplitude reveal lower levels of brain activity. In the case of specific wave types, the alpha wave pattern includes 8-12 cycles per second, while the theta wave pattern includes 4-7 cycles per second (Epstein and Mardon 13-14). Therefore, during this first stage of sleep, the transition from alpha waves to theta waves shows the decline in brain activity. The second stage of sleep, a type of transition stage, occurs periodically throughout the night in approximately ten to twenty- five minute intervals (Epstein and Mardon 15). People typically spend about half of the night in this stage as they enter and re-enter it multiple times in between other stages. Further testing reveals that this phase involves still eyes, a slower heart and breathing rate, and sporadic brain activity (Epstein and Mardon 15). As Epstein explains it, this sporadic brain activity presents itself through multiple sets of a “brief [burst] of fast activity called sleep spindles . . . [and] a K-complex, which scientists think represents a sort of built-in vigilance system that keeps you posed to be awakened if necessary” (15). The discovery of these types of brain activity further emphasizes the level to which sleep is truly an active process. The next two stages fall under the category of deep sleep. As the name implies, stages three and four involve a deeper level in which much of the restorative properties come into effect. For the average sleeper, the sum of these thirty-minute segments typically constitutes about twenty percent of a single night of sleep (Epstein and Mardon 16). During this time, the brain waves transition again,