During a polysomnography study, what would indicate a successful arousal from sleep?

The correct answer points to the specific characteristics observed in the electroencephalogram (EEG) that signify an arousal from sleep. During a successful arousal from sleep, it is common to see an observable increase in EEG frequency, which means that the brain is transitioning to a more alert state. This shift in frequency is often accompanied by a decrease in amplitude, indicating less synchronized brain activity typical of deeper sleep stages.

This combination of higher frequency and lower amplitude reflects the brain's shift from a sleep state (where slower, high-amplitude waves dominate) to a waking state where the brain becomes more active and alert. The EEG changes are critical in polysomnography as they provide direct evidence of the brain's state during the sleep study.

Other choices do not directly indicate a successful arousal from sleep. An increase in heart rate can occur during various sleep stages and may not specifically reflect an arousal. A decrease in blood oxygen levels is usually associated with respiratory events during sleep rather than an arousal. Lastly, a sudden movement of the limbs might not be a reliable indicator of arousal, as limb movements can occur during sleep for various reasons, including periodic limb movement disorder, without necessarily indicating that the individual has awakened.