Which of the following is NOT a feature of active sleep in infants?

In active sleep, also known as REM (Rapid Eye Movement) sleep, infants exhibit several distinct characteristics that differentiate it from other sleep states. Among these features is reduced muscle tone, which is typical during REM sleep. This reduced muscle tone allows for the jerky movements and twitching commonly observed in this stage, reflecting a state of muscle relaxation.

Frequent irregular breathing is also typical during active sleep, as the respiratory patterns can vary and may not maintain a regular rhythm. Additionally, the presence of active eye movements is a hallmark of this stage of sleep, where the eyes move under the eyelids signifying increased brain activity.

Grunting sounds may be heard in infants and can occur in various contexts, but they do not serve as a distinguishing feature of active sleep. While some infants may grunt during this sleep stage due to other reasons such as gastrointestinal discomfort or transitioning between sleep states, it is not a defining characteristic of active sleep itself.

Thus, reduced muscle tone is indeed a typical feature of active sleep, making this understanding critical for anyone studying sleep patterns in infants.