Chronobiology and Circadian Rhythms — MCQs

Chronobiology and Circadian Rhythms Indian Medical PG Practice Questions and MCQs

Question 41: Which one of the following phenomena is closely associated with slow-wave sleep?

A. Dreaming
B. Atonia
C. Irregular heart rate
D. Sleepwalking (Correct Answer)

Explanation: ***Sleepwalking*** - **Sleepwalking** (somnambulism) is a **parasomnia** that typically occurs during **slow-wave sleep (SWS)**, particularly in stages N3. - During SWS, the brain waves are slow, and the body's motor systems can still be active, leading to complex behaviors like walking while asleep. *Dreaming* - While dreams can occur in all sleep stages, **vivid and elaborate dreams** are most strongly associated with **REM (rapid eye movement) sleep**. - Dreams in **SWS** tend to be less vivid, more fragmented, and less emotionally charged. *Atonia* - **Atonia**, or muscle paralysis, is a hallmark feature of **REM sleep**, which prevents individuals from acting out their dreams. - In contrast, **muscle tone is typically maintained** during slow-wave sleep. *Irregular heart rate* - An **irregular heart rate** can be a feature of **REM sleep**, where autonomic nervous system activity is highly variable alongside rapid eye movements. - During **slow-wave sleep**, physiological functions such as heart rate tend to be **slowed and regular**, reflecting deep relaxation.

Question 42: A 72-year-old woman with insomnia participates in a sleep study. As part of the study protocol, she has EEG leads attached, then goes to sleep. At one point during the evening, 12-16 Hz sleep spindles and K-complexes are observed. Which stage of sleep is associated with this pattern?

A. REM
B. Stage 1
C. Stage 2 (Correct Answer)
D. Stage 3

Explanation: ***Stage 2*** - **Sleep spindles** (12-16 Hz bursts) and **K-complexes** (high-amplitude negative deflection followed by a positive component) are the definitive EEG markers of **Stage 2 non-REM sleep**. - This stage represents a deeper level of sleep than Stage 1, where the body begins to relax more, and eye movements cease. *REM* - **REM sleep** is characterized by low-voltage, mixed-frequency EEG activity resembling wakefulness, along with **rapid eye movements** and muscle atonia. - While dreaming is prevalent during REM, **sleep spindles** and **K-complexes** are notably absent. *Stage 1* - **Stage 1 (N1 non-REM sleep)** is the transition from wakefulness to sleep, marked by the disappearance of alpha waves and the appearance of **theta waves** (3-7 Hz). - It does not contain **sleep spindles** or **K-complexes**, which are characteristic of deeper sleep stages. *Stage 3* - **Stage 3 (N3 non-REM sleep)**, commonly known as **deep sleep** or **slow-wave sleep**, is defined by the presence of **delta waves** (0.5-2 Hz) accounting for 20% or more of the EEG. - Although it is a deeper stage of sleep, **sleep spindles** and **K-complexes** are not the primary defining features; **delta wave activity** predominates.

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