Normal Sleep EEG Background Organization
Normal Sleep EEG Background Organization[edit | edit source]
Sleep is divided into two states: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep is further subdivided into N1-3 based on the depth of sleep and certain EEG characteristics.
The onset of N1 sleep is characterized by an attenuation of the posterior dominant rhythm, increased theta activity, reduction in muscle movements and slow roving eye movements.
The appearance of hypnagogic hypersynchrony and triangular vertex waves that have a phase reversal across the midline also herald development of N1 sleep.
As sleep deepens into N2, vertex waves and sleep spindles become more apparent. Since sleep transients are best seen in the central regions, a transverse montage brings them out. During arousals K-complexes can appear (next page)
K-complexes during N2 Sleep are high voltage, broad, triangular, often biphasic deflections that are maximal in the frontal and vertex leads and often trailed by spindles. Also note sharp, triangular, monophasic waveforms in the occipital leads – Positive Occipital Sharp Transients of Sleep (POSTS) – a normal variant seen in N1 and N2 sleep.
N3 sleep is characterized by the increasing percentage of high voltage delta waves of >20% of the epoch. Previously these were divided into two stages: stage 3 and 4 sleep where the delta activity comprises approximately 20-50% of the record, and in stage 4 the delta activity comprises more than 50% of the record.
REM sleep has the electrophysiologic characteristics of a low voltage mixed frequency background without evidence of a posterior dominant rhythm, temporal theta called saw tooth waves and rapid eye movements that are usually lateral or oblique in direction. There is a noticeable lack of movement or muscle artifact during this period of time due to physiologic atonia.