ABSTRACT
Two sleep states, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep, can be distinguished on the basis of several physiological measures. Large numbers of cerebral cortical cells fire in synchrony and consequently their summed activity produces potentials large enough that they can be recorded with an array of scalp electrodes as electroencephalography (EEG). The EEG waveform varies in frequency and the frequency ranges are conventionally grouped: alpha (8-13 Hz), beta (13-30 Hz), delta (0.5-2 Hz), and theta (4-7 Hz). When awake, the EEG waveforms are of low amplitude and high (alpha) frequency (Figure 1) and are described as desynchronized. Non-REM (NREM) sleep, has high-amplitude, low-frequency (synchronized) EEG waveforms.
