Muscle activity and postural behaviour in newborn infants. A polymyographic study

Area of Science:

• Neonatal physiology
• Neuroscience
• Developmental motor control

Background:

• Understanding spontaneous muscle activity in newborns is crucial for assessing neurological development.
• Previous research has explored neonatal motor patterns, but detailed analysis of tonic activity across behavioral states is limited.

Purpose of the Study:

• To analyze spontaneous electromyography (EMG) activity of various muscles in healthy newborns during different behavioral states.
• To characterize tonic muscle activity patterns, particularly in state 1 (quiet sleep), and their relationship to postural behavior and state transitions.

Main Methods:

• Surface electromyography (EMG) was used to record muscle activity in 9 healthy newborns on days 5-6 of life for 6-8 hours.
• Infants were positioned in alternating side positions.
• Averaged EMG activities were analyzed in relation to behavioral states (state 1 and state 2) and postural behavior, using an improved recording technique and logarithmic presentation.

Main Results:

• Chin muscles exhibited the most specific EMG pattern in state 1, with tonic activity present only 15% of the time and increasing stepwise after phasic activity.
• Other muscles, including neck and forearm, showed less tonic activity in state 1, with durations varying by muscle group.
• Tonic activity exceeding 30 seconds was absent in state 2, except during transitions. Muscles in the chin, neck, and upper extremities were more active than lower extremities in both states.

Conclusions:

• Sustained tonic activity in newborns, particularly in state 1, may be linked to an increased gain in the gamma-loop, potentially influencing respiratory regularity.
• Observed muscle activity differences reflect maturational and functional variations between muscle groups.
• Systematic changes in body position did not consistently affect motility or tonic activity.