Concordance between surface and intra-muscular recordings of facial emg during emotional expression

Needle and surface EMG recordings were made from the left corrugator supercilii and zygomaticus major muscles, and the skin overlying them, in 12 right-handed normal subjects during imagined and posed sad, happy and angry states. The surface and needle EMG recordings showed good correspondence for the corrugator and zygomaticus major muscles within each individual subject. Considerable inter-subject and inter-emotion variability was, however, observed. The surface to needle concordance was poor when the EMG activity itself was low. While this study does not suggest that specific surface EMG recordings from the face are inappropriate, it provides a note of caution when the activity is low.