402 Sleep-Wake Disorders
Diagnostic Markers
NREM sleep arousal disorders arise from an y stage of NREM sleep but most commonly
from deep NREM sleep (slow-wave sleep). They are most likely to appear in the first third
of the night and do not commonly occur duri ng daytime naps. During the episode, the
polysomnogram may be obscured with movement artifact. In the absence of such artifact,
the electroencephalogram typically shows theta or alpha frequency activity during the ep-
isode, indicating partial or incomplete arousal. 
Polysomnography in conjunctio n with audiovisual monitoring  can be used to document
episodes of sleepwalking. In the absence of ac tually capturing an event during a polysomno-
graphic recording, there are no polysomnogra phic features that can serve as a marker for
sleepwalking. Sleep deprivation may increase the likelihood of capturing an event. As a group,
individuals who sleepwalk show instability of de ep NREM sleep, but th e overlap in findings
with individuals who do not sleepwalk is great en ough to preclude use of this indicator in es-
tablishing a diagnosis. Unlike arousals from RE M sleep associated with nightmares, in which
there is an increase in heart rate and respiratio n prior to the arousal, the NREM sleep arousals
of sleep terrors begin precipitou sly from sleep, without anticipatory autonomic changes. The
arousals are associated with impressive autono mic activity, with doubling or tripling of
the heart rate. The pathophysiology is poorly unde rstood, but there appears to be instability in
the deeper stages of NREM sleep. Absent capturing an event during a formal sleep study,
there are no reliable polysomnographic indicators  of the tendency to experience sleep terrors.
Functional Consequences of