The document summarizes the stages of sleep as assessed by polysomnography. It describes the key EEG patterns, eye movements, and muscle activity that characterize each stage: Stage 1 is characterized by low voltage mixed frequency EEG activity, vertex sharp waves, and slow eye movements. Stage 2 involves sleep spindles and K complexes in the EEG along with occasional slow eye movements. Stage 3 contains 20-50% slow wave activity in the EEG. REM sleep involves rapid eye movements and EEG desynchronization resembling wakefulness, along with muscle atonia. The stages cycle throughout the night in a progression from light to deep sleep and back to light sleep.

1. Sleep EEG
DR VAISHAL SHAH
SR NEUROLOGY
GMC KOTA

2. Introduction
Sleep is not homogeneous. Composed of NREM and REM sleep.
Stages N1 and N2 are called light sleep and stage N3 is called deep or slow-wave
sleep.
Characterized by sleep stages based on EEG , EOG or eye movements, and
electromyographic (EMG) or muscle electrical activity.
Usually 4 or 5 cycles of sleep, each composed of a segment of NREM sleep
followed by REM sleep.

3. Introduction
Periods of wake may also interrupt sleep during the night.
As the night progresses, the length of REM sleep in each cycle usually increases.

4. Introduction
Wakefulness within sleep usually accounts for less than 5 percent of the night.
Stage 1 sleep generally comprises about 2 to 5 percent of sleep.
Stage 2 sleep generally comprises about 45 to 55 percent of sleep.
Stage 3 sleep generally comprises about 3 to 8 percent of sleep.

5. Introduction
Stage 4 sleep generally comprises about 10 to 15 percent of sleep.
NREM sleep, is therefore, is usually 75 to 80 percent of total sleep.
REM sleep is usually 20 to 25 percent of total sleep, occurring in four to six
discrete episodes.

10. Wake
•Close eye wakefullness
Alpha rhythm over occipital region > 50% of epoch with eye closure, slow-rolling
eye movements.
•Open eyes wakefulness
Beta rhythm, conjugate vertical eye blinks, Rapid horizontal eye movements with
high chin tone.

12. Stage 1 NREM
Low voltage, Mixed frequency activity ( 4 -7Hz )
< 50% of a epoch contains alpha waves and other criteria for deeper sleep stages
are not met.
SREM becomes regular and mandibular muscle tone starts reducing in EMG
elecrodes.

13. Stage 1 NREM
•Slow rolling eye movements (SREMs)
•Attenuation (drop out) of the alpha rhythm
•Central or frontocentral theta activity
•Positive occipital sharp transients of sleep (POSTS)
•Vertex sharp transients
•Hypnagogic hypersynchrony

14. Slow rolling eye movements (SREMs)
SREMs are usually the first evidence of drowsiness seen on the EEG.
Best seen in F7 and F8.
Slow (ie, typically 0.25-0.5 Hz).
SREMs disappear in stage II and deeper sleep stages.

15. Attenuation (drop out) of the alpha
rhythm
Drop out of alpha activity typically occurs together with or nearby SREM
The alpha rhythm gradually becomes slower, less prominent, and
fragmented.

18. Positive occipital sharp transients of
sleep
POSTS start to occur in healthy people at 4 years, become fairly common
by 15 years, remain common through 35 years, and start to disappear by
age 50 years.
More common during daytime naps than during nocturnal sleep.
Morphology – “Reverse check mark”. Amplitude – 50-100 microvolt.
Symmetrical. 4-5 Hz. Might persist in stage 2 but disappear afterwards.

21. Vertex sharp transient
V waves.
These transients are almost universal.
Like k complexes, vertex waves are maximum at the vertex (central midline
placement of electrodes [cz]), so that, depending on the montage, they may be
seen on both sides, usually symmetrically
Their amplitude is 50-150 mv.

22. Vertex sharp transient
They can be contoured sharply and occur in repetitive runs, especially in
children.
Might persist in stage 2 but disappear in subsequent stages.
Narrower, more focal compared to k complex.

24. Hypnagogic hypersynchrony
Hypnagogic hypersynchrony is a well-recognized normal variant of drowsiness in
children aged 3 months to 13 years.
Described as paroxysmal bursts (3-5 Hz) of high-voltage (as high as 350
microvolt) sinusoidal waves, maximally expressed in the prefrontal-central
areas.

27. Stage 2 NREM
To qualify as stage N2, an epoch also must contain less than 20% of slow (delta) wave
EEG activity(<6 seconds of a 30-second epoch).
The distinct and principal EEG criterion - appearance of sleep spindles or K complexes.
The presence of sleep spindles is necessary and sufficient to define stage II sleep.
Except for slow rolling eye movements, all patterns described under stage I persist in
stage II sleep.

28. Sleep spindles
Normally first appear in infants aged 6-8 weeks and are bilaterally asynchronous.
These become well-formed spindles and bilaterally synchronous by the time the
individual is aged 2 years.
Frequency of 12-16 hz (typically 14 hz) and are maximal in the central region
(vertex), although they occasionally predominate in the frontal regions.
Amplitude is usually 20-100 mV

29. Sleep spindles
Occur in short bursts of waxing and waning spindlelike (fusiform) rhythmic
activity.
Extreme spindles are unusually high-voltage (100-400 mV) and prolonged (>20 s)
spindles located over the frontal regions.

32. K complexes
High amplitude (>100 microvolt), broad (>200 ms), diphasic, and transient and
often are associated with sleep spindles.
Location is frontocentral, with a typical maximum at the midline electrodes cz &
fz.

37. Stage 3 NREM (formerly stage N3 and N4)
Slow-wave activity (frequency < 2 hz and amplitude > 75 mv peak-to-peak) is
present for greater than 20% of the epoch.
In older patients, the slow-wave amplitude is lower and the total amount of
slow-wave sleep is reduced.

38. Stage 3 NREM (formerly stage N3 and N4)
20-29 years spend about 21% of their total sleep in SWS,
40-49 years spend about 8% in SWS,
60-69 spend about 2% in SWS.

39. Stage 3 NREM (formerly stage N3 and N4)
Typically, stage N3 occurs mostly in the early portions of the night. Several
parasomnias (disorders associated with sleep) occur in stage N3 sleep and,
therefore, can be predicted to occur in the early part of the night.
These include somnambulism (sleep walking) and night terrors.
By contrast, parasomnias occurring in REM sleep (for example, nightmares) are
more common in the early morning hours.

41. REM sleep
By strict sleep staging criteria on polysomnography, REM sleep is defined by
(1) rapid eye movements
(2) muscle atonia
(3) EEG “desynchronization” (compared to slow wave sleep).
In addition to the 3 features, “saw tooth” waves also are seen in REM sleep.

42. EEG desynchronization
The EEG background activity changes from that seen in slow wave sleep (stage III
or IV) to faster and lower voltage activity (theta and beta), resembling
wakefulness.
Saw tooth waves are a special type of central theta activity that has a notched
morphology resembling the blade of a saw and usually occurs close to rapid eye
movements.
Rapid eye movements: These are saccadic, predominantly horizontal, and occur
in repetitive bursts.

46. Outline
Stage 1
EEG: Relatively low voltage, mixed frequency alpha and theta; Vertex sharp
waves.
EMG: Tonic activity, may be slight decrease from waking.
EOG: Slow eye movements

47. Stage 2
EEG: Sleep spindles (waxing and waning at 12-14 cps, ≥ 0.5 sec); K complex
(negative sharp wave followed immediately by slower positive components;
maximal in vertex; spontaneous or in response to sound)
EMG: Tonic activity, low level
EOG: Occasionally slow eye movements near sleep onset

48. Stage 3
EEG: ≥ 20 ≤ 50% high amplitude (> 75 V), slow frequency (≤ 2 cps); maximal in
the frontal
EMG: Tonic activity, low level
EOG: None, picks up EEG
Stage 4
EEG: >50% high amplitude, slow frequency
EMG: Tonic activity, low level
EOG: None, picks up EEG

50. Thank you