Which of the following is not true of muscle artifact?

Muscle artifact refers to signals picked up by the electroencephalography (EEG) or electromyography (EMG) systems that are produced by muscle activity rather than brain activity. Understanding this concept helps clarify why a specific statement about addressing muscle artifact is not correct.

When muscle artifacts occur, they can significantly obscure the underlying brain activity shown in EEG recordings, which makes accurate scoring of sleep stages challenging. Therefore, recognizing that muscle activity often manifests as artifacts emphasizes option C's relevance in understanding the implications of muscle activity on data quality.

The other statements reflect accurate observations about muscle artifact. It's commonly observed when the patient is anxious or tense, as highlighted in option A, due to increased muscle tone related to stress. Option B supports the idea that muscle artifacts can diminish as the patient relaxes and falls asleep, leading to reduced muscle activity and therefore clearer signals.

However, the use of a notch filter is typically aimed at eliminating specific frequency interference (like 60 Hz electrical noise) rather than resolving muscle artifacts, which stem from physiological movements. Hence, believing that muscle artifacts can be best corrected by a notch filter presents a misunderstanding of the nature of muscle activity versus types of electrical interference.