Based on EEG, EMG and electro-oculography patterns, four types (or
stages) of sleep can be identified (Table I.4.3 and Figure I.4.1). In an individual
without sleep abnormalities, non-rapid eye movement (NREM) and rapid eye
movement (REM) phases alternate in a cyclic manner, each cycle lasting on average
from 90 to 110 minutes. During a normal sleep period in adults, 4–6 such cycles
are noted (Figure I.4.2). It is important to be aware of this alternation because
certain abnormal motor activities are characteristically associated with NREM or
REM stages.
The term sleep macro-architecture refers to the description of sleep in terms
of sleep states (wakefulness vs. sleep) and stages, sleep cycles (NREM/REM), sleep