STAGES OF SLEEP

- Dr. Jeet Nadpara

Nearly one third of human life is spent in sleep, an easily reversible state of relative unresponsiveness and serenity which occurs more or less regularly and repetitively each day.

States and stages of Sleep

States and stages of human sleep are defined on the basis of characteristic patterns in the electroencephalogram (EEG), electro-oculogram (EOG a measure of eye movement activity), and the surface electromyogram (EMG).

The continuous recording of this array of electro-physiologic parameters to define sleep and wakefulness is termed polysomnography.

Polysomnographic profiles define two states of sleep:

1. Rapid eye movement (REM) sleep (also known as dreaming,

paradoxical, desynchronized, or ‘D’sleep)and,

2. Non rapid eye movement (NREM)sleep (also known as orthodox, synchronized or ‘S’ sleep). NREM sleep is in turn subdivided into four stage.

1. NREM stage 1 is the transition from wakefulness and is characterized by disappearance of regular alpha pattern and emergence of a low-amplitude, mixed frequency pattern, pre dominantly in the theta range (2 to 7 Hz)and slow ‘rolling’ eye movement.

2. NREM stage 2 is defined by the occurrence of K complexes and sleep spindles superimposed upon a background activities similar to that of stage 1.

K complexes are slow, high amplitude, negative(upward) discharges followed immediately by a (upward) discharges followed immediately by a positive downward reflection.

Sleep spindles are high frequency(12 to 14 hz) discharge lasting 0.5 to 0.2 seconds with a characteristic waxing and waning amplitude. Rapid eye movement activity is absent, and EMG is similar to stage 1.

3. NREM stage 3 is sleep with at least 20 percent but less than 50 percent high amplitude (75V) delta (0.5 to 2 Hz) activity. Sleep spindles may persist, eye movement activity is absent, and EMG activity perist at reduced level.

4. In NREM stage 4, the high voltage, slow EEG pattern of stage 3 comprises at least 50 percent of the record.NREM stage 3 and stage 4 are referred to, collectively,as a ‘slow wave’, ‘delta’, or deep sleep.

REM sleep is characterized by a low amplitude, mixed frequency EEG similar to that of a NREM stage 1. Burst of 3 to 5 Hz activity with sharp negative deflection are often superimposed on this pattern.

The EOG shows burst of REM similar to that seen during eye opening in wakefulness.EMG activity is absent, reflecting the complete brainstem-mediated muscle atonia that is characteristic of that state.

Electroencephalogram Electro-oculogram Electromyogram

Wake (eye open) Low amplitude, mixed,High frequency

Rapid High variable

Wake (eye closed) Low amplitude, alpha (8-13Hz)dominates over occipital region

Absent but slow rolling eye movements

Reduced

NREM stage 1 Low amplitude, mixed frequency(alpha absent)

Slow rolling eye movements

Reduced

NREM stage 2 Low amplitude,K complexes and sleep spindles

Absent Reduced

NREM stage 3 Increased amplitude,Decreased frequency,20 to 30 % delta

Absent Reduced

NREM stage 4 >50% dominated by deltaEEG activity

Absent Reduced

REM Low amplitude, mixed frequency

Rapid, conjugate Absent

Organization of human sleep

• After sleep onset, sleep usually progresses through NREM stage 1 to 4 within 45 to 60 min.

• After the first slow wave sleep episode, the progression of NREM stage reverses.

• The first REM sleep occurs usually not less than 80 min. after sleep begins, although REM latency shortens with advance age.

• More rapid onset REM sleep in young adult may (particularly if less than 30 min) suggestpathology such as endogenous depression, narcolepsy, circadian rhythm disorders, or drug withdrawal.

• NREM and REM alternate through the night with an average cycle of 90 to 110 min.

• As the sleep period lengthens, the proportion of each cycle composed of slow waveSleep decreases and that of REM increases.

• Overall, REM sleep is 20 to 25 percent of total sleep, while NREM stage (1to 2) constitute50 to 60 percent (increasing in elderly subjects).

Thank you !