Figure 2. Cortical electroencephalogram recorded during wakefulness, nonrapid eye movement sleep, rapid eye movement sleep, and halothane anesthesia. The low amplitude, high frequency electroencephalogram of wakefulness (WAKE) is similar to the EEG recorded during rapid eye movement (REM) sleep. [9]Non-REM sleep (NREM) is characterized by high amplitude (> 100 micro V) synchronized waves with frequencies of 8-14 Hz (called spindles). The lower tracing in the center shows that electroencephalogram spindles during halothane anesthesia are similar to electroencephalogram spindles of NREM sleep. The right-most traces show a single spindle with an expanded time-scale during NREM sleep (top) and during halothane anesthesia (bottom).