Correlation between the dischanges of two simultaneously recorded motor units and physiological tremor

Area of Science:

• Neuroscience
• Motor Control
• Physiology

Background:

• Physiological tremor is a rhythmic, involuntary movement.
• The precise neural mechanisms underlying tremor generation remain incompletely understood.
• Motor unit activity is fundamental to muscle contraction and force production.

Purpose of the Study:

• To investigate the relationship between motor unit synchronization and physiological tremor.
• To determine if synchronized motor unit activity contributes to tremor force.
• To explore potential implications for neurological disorders affecting tremor.

Main Methods:

• Simultaneous recording of pairs of motor units from intrinsic hand (first dorsal interosseus) and calf (gastrocnemius and soleus) muscles.
• Isometric contractions of varying strengths were performed.
• Cross-correlation analysis was used to assess synchronization between motor units and between motor unit firing and tremor peaks.

Main Results:

• A consistent tendency for synchronization was observed between pairs of motor units in both hand and calf muscles.
• This synchronization exceeded levels expected from random asynchronous firing.
• The degree of motor unit synchronization positively correlated with the amplitude of physiological tremor.
• Motor unit firing often preceded tremor peaks by 30-60 milliseconds.

Conclusions:

• The force generated by physiological tremor is a result of synchronized motor unit activity.
• This finding is supported by tremor alterations observed in Parkinson's disease and myopathies, reflecting changes in motoneuronal firing rates.