A “phases score” is a method used in sleep science to analyze and understand the distinct stages of sleep. It provides a detailed breakdown of how an individual progresses through sleep, offering insights beyond just the total hours slept.
Understanding the Stages of Sleep
Sleep is broadly categorized into two main types: Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. NREM sleep accounts for approximately 75% of total sleep time in adults and is further divided into three distinct stages, each progressively deeper.
The first NREM stage, N1, is a transitional phase marking the shift from wakefulness to sleep. During N1, brain activity begins to slow, and it is easy to be awakened. Stage N2, or light sleep, comprises 50% of an adult’s total sleep and is characterized by a further decrease in body temperature, relaxation of muscles, and slowing of heart and breathing rates. Brain activity in N2 includes specific patterns like sleep spindles and K-complexes, which help maintain sleep despite external stimuli.
The deepest NREM stage, N3, is also known as slow-wave sleep or deep sleep, and is when the body undertakes significant recovery and growth. Brain activity during N3 is dominated by slow, high-amplitude delta waves, making it the most difficult stage to awaken from. Following NREM sleep, the body enters REM sleep.
REM sleep is characterized by rapid eye movements, increased brain activity resembling wakefulness, and temporary muscle paralysis. This stage is strongly associated with vivid dreaming and plays a role in memory consolidation, learning, and emotional regulation.
Measuring Sleep Phases
Sleep phases are identified and quantified primarily through polysomnography (PSG). This comprehensive test monitors several physiological signals throughout the night to create a detailed record of sleep architecture.
Electrodes placed on the scalp record brain waves (EEG), revealing distinct patterns for different sleep stages. NREM stages show progressively slower brain waves, while REM sleep exhibits patterns similar to wakefulness. Sensors near the eyes track eye movements (EOG), useful for identifying the rapid eye movements characteristic of REM sleep. Electrodes on the chin and legs measure muscle activity (EMG), detecting muscle relaxation in NREM stages and the temporary paralysis that occurs during REM. These combined signals allow trained professionals or specialized algorithms to classify sleep into 30-second segments, assigning each to a specific sleep phase.
This detailed analysis of physiological signals provides a precise timeline of an individual’s journey through NREM stages (N1, N2, N3) and REM sleep, as well as periods of wakefulness.
What a “Phases Score” Reveals About Your Sleep
A phases score details the distribution and proportion of time spent in each sleep phase, such as deep sleep (N3) and REM sleep. For adults, percentages of total sleep time are 5% in N1, 50% in N2, 20% in N3, and 25% in REM sleep.
The balance of time spent in each sleep stage is associated with feeling rested and having sufficient mental and physical energy. Adequate deep sleep (N3) supports bodily recovery, growth, and immune function. Sufficient REM sleep contributes to brain function, memory consolidation, and emotional health.
A phases score can highlight imbalances or disruptions in these patterns, offering clues about a person’s sleep architecture. For instance, a high percentage of N1 sleep may suggest frequent awakenings or sleep disruptions. A low percentage of N3 or REM sleep could indicate that the sleep is not as restorative as it should be, even if the total sleep duration seems adequate.