Sleep is a naturally recurring state of mind and body, characterized by altered consciousness, relatively inhibited sensory activity, inhibition of nearly all voluntary muscles, and reduced interactions with surroundings. Adequate sleep is vital for good mental health, and there is a bidirectional relationship between neuropsychiatric disorders and sleep.[1]
The most common sleep disorders include:
Measuring sleep quality can be done through scales, questionnaires, and sleep diaries:
Name | Rater | Description | Download |
---|---|---|---|
Epworth Sleepiness Scale (ESS) | Patient | The ESS is a self-administered questionnaire with 8 questions. | ESS Information |
Insomnia Severity Index (ISI) | Patient | The ISI has seven questions rated on a scale of 0 to 4.[10] | ISI Download |
Pittsburgh Sleep Quality Index (PSQI) | Patient | The PSQI is an effective instrument used to measure the quality and patterns of sleep in adults. It differentiates “poor” from “good” sleep quality by measuring 7 components. | PSQI Download |
Sleep can be measured objectively in one of several ways:
Sleep consists of two physiological states: non-rapid eye movement sleep (known as NREM) and rapid eye movement sleep (also known as REM):
Stage of Sleep | % Total Sleep Time | Description | Function | EEG | Eye Movements | Muscle Tone |
---|---|---|---|---|---|---|
Awake (eyes open) | - | • Alert and active mental focus | Wakefulness | • Beta, 15–60 Hz • This is the highest frequency, lowest amplitude EEG | Eyes move and blink | High voluntary tonic activity |
Awake (eyes closed) | - | • Restful state but not sleeping | Wakefulness | Alpha waves, 8-12 Hz | Eyes move | High voluntary tonic activity |
Stage N1 (Stage 1) | 5% | • Also known as “light sleep.” It is the transition from wakefulness → sleep and vice versa • Individuals may often be in this stage and think they are “not sleeping.” • Increased light quality sleep indicates sleep disruption | Prominent alpha waves = becoming more drowsy | • Theta waves (low amplitude, mixed frequency), 4-8 Hz and some alpha waves, 8-12 Hz • In N1, alpha makes <50% of EEG and is mixed with theta waves • Note that N1 can be very similar to a waking EEG | Slow rolling eye movements (SREMs) are usually the first evidence of drowsiness seen on the EEG | Decreasing levels of high tonic activity |
Stage N2 (Stage 2) | 50% | • Most of the night is spent in N2! • Sleep spindles and K-complexes emerge during this stage and are thought to be the brain's way of evaluating potential threats (i.e. - external stimuli) while sleeping and to dampen arousals if the threats are not real. | • Sleep spindles (Sigma waves), 11-16 Hz • K-complexes (negative sharp wave followed by positive slow waves), 12-14 Hz | None | Low tonic activity | |
Stage N3 (Stage 3 and 4) | 10-20% | • The “deepest” stage and hardest to awaken, also called Slow Wave Sleep (SWS) • Associated with sleep inertia when awoken in this stage • It is also the most restorative sleep. | This is homeostatic sleep (reduced BP, HR, cardiac output, RR). Growth hormone is released. | • Delta waves, 0.5-4 Hz • This is the lowest frequency, highest amplitude EEG | None | Low tonic activity |
Rapid Eye Movement (REM) | 25% | • A “paradoxical state” that resembles awake state, except there is muscle • Arousal with increased oxygen use, increased variability of autonomic state (BP, HR). Increased brain temperature, cerebral glucose metabolism and cerebral blood flow. • Release of acetylcholine in the cortex is highest during wakefulness and also during REM sleep. • Occurs every 90 minutes, and REM length grows longer through the night. | Cognitive sleep, learning, cognitive restructuring. | • High (fast waves) and mixed frequency, with low voltage • Also includes: saw-tooth waves, theta activity, and slow alpha activity • Looks similar to EEG of awake individual with their eyes closed | Rapid eye movement | Almost total muscle paralysis (during tonic phase of REM). There can be very brief movement during phasic periods. |
BAT-D
(Think of a bat!) can be used to remember the order of brain waves from wakefulness → deep sleep. Also, using the Greek letters, you can correspond the symbols to the lower bounds Hz of each wave.B
- Beta (β) [β looks like the numbers 1 and 3 mashed up – 13 Hz (lower bound)]A
- Alpha (α) [α looks like half of an 8 – 8 Hz (lower bound)]T
- Theta (Θ) [Θ looks partially like a 4 – 4 Hz (lower bound)]D
- Delta (δ) 2
is when bruxism (two
th grinding) occursIn early in life, about half of sleep time is spent in REM sleep. By adulthood, about 20% of sleep is REM sleep. REM sleep continues to decrease into old age. Older adults generally have more insomnia, find it harder to stay up late (due to relative advance of sleep phase), and have more shallow sleep. Sleep disruptions are common, including more brief awakenings. Sleep may also be less restorative, and there may be daytime sleepiness.
Insomnia is more prevalent in late life and sleep problems in the elderly are often mistakenly considered a normal part of aging. Sleep disturbance in older adults is associated with cognitive impairment, poor concentration, and decreased day-to-day functional performance. One of the challenges in identifying sleep disorders in older adults is that sleep architecture naturally changes significantly in healthy older adults (figure 4). In general with older adults:
In narcolepsy, changes in sleep include:
Characteristic changes are seen in REM sleep in depression including:[16]