Which of these electrode sites is not typically used in a baseline montage?

In a baseline montage, the goal is to establish a standard reference for monitoring brain activity, typically focusing on the scalp and other areas directly related to sleep studies. The electrodes generally used in this context are primarily concerned with measuring electrical activity of the brain, as well as some physiological metrics.

Arm EMG, while it is used to detect muscle movements and can be part of a comprehensive sleep study to capture artifacts or movements, is not included in the baseline montage. Baseline montages typically emphasize brainwave activity using cranial electrodes and may incorporate other physiological monitors like E2 for respiratory patterns, Leg EMG for leg movements, or thoracic belts to track respiratory effort.

This delineation indicates that arm EMG is ancillary rather than fundamental to establishing a baseline of brain electrical activity, making it the electrode site not conventionally part of a baseline montage.