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Motor unit synchronization in physiologic, enhanced physiologic, and voluntary tremor in man
E L Logigian1, M M Wierzbicka, F Bruyninckx
1Department of Neurology, Harvard Medical School, Massachusetts General Hospital, Boston, MA.
Annals of Neurology
|March 1, 1988
Summary
Motor unit synchronization increases with tremor amplitude, suggesting it underlies tremor generation. This study quantifies motor unit synchronization during different tremor types and voluntary movements.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Motor unit synchronization is hypothesized to be the physiological basis for tremor.
- Understanding the relationship between motor unit activity and tremor is crucial for diagnosing and treating movement disorders.
Purpose of the Study:
- To quantify motor unit synchronization during physiologic tremor (PT), enhanced physiologic tremor (EPT), and voluntary tremor-like movements (VT).
- To investigate the relationship between motor unit synchronization, tremor amplitude, and firing frequencies.
Main Methods:
- Simultaneous recording of pairs of single motor units from wrist extensor muscles in three subjects.
- Analysis of spike trains using cross-correlation histograms to assess synchronization.
- Quantitative index of synchronization (relative peak area) calculated for each motor unit pair.
Main Results:
- Motor unit synchronization was present in PT, EPT, and VT, with varying degrees.
- Synchronization index was lowest in PT, increased with tremor amplitude in EPT, and was highest in VT.
- Synchronization patterns differed based on motor unit firing frequencies, especially in higher amplitude tremors and voluntary movements.
Conclusions:
- Motor unit synchronization increases with tremor amplitude, supporting the hypothesis that it is the physiological basis for tremor.
- Increased muscle spindle afferent activity and common synaptic input may contribute to enhanced synchronization in EPT and VT, respectively.