The five stages of sleep are differentiated from each other by
a) varying levels of adrenaline found in the blood
b) varying patterns of brain activity
c) whether you are dreaming or not
d) your core body temperature

Sleep stages are differentiated by different patterns of brain activity.

Explanation:

The nerve cells in brain controls and affects sleep. The five stages of sleep goes through the two main stages of Rapid and non-rapid eye movement, known as REM and NREM. All these are dependent on the activity of the brain while sleeping.

The first stage of sleep occurs when the brain works between consciousness and unconsciousness, in the second stage the brain waves slowly bursting of waves occur, in the third and fourth stage the brain waves slowly with irregular faster waves occurring in sleep and in the last stage the brain rests and the heart functions rapidly.

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