The EEG pattern of a term infant, equivalent to the expected date of birth, is a key clinical assessment. When an infant has been fed and falls asleep, active sleep (AS) appears first. When AS is recorded using a polygraph, irregular heart rate and respiration, low chin electromyogram (EMG) activity, and rapid eye movement (REM) are observed. This sleep stage corresponds to REM sleep in adults (Table 3.1). During the AS stage after falling asleep, a mixed (M) pattern is mainly observed in which high-voltage slow waves intermittently appear and physiological transients are prominent. Subsequently, polygraphic parameters gradually indicate that body movements decrease, heart rate and respiration become regular, chin EMG activities gradually increase, and startle-like body movements are sometimes observed.