Load-independent contributions from motor-unit synchronization to human physiological tremor
D M Halliday1, B A Conway, S F Farmer
1Division of Neuroscience and Biomedical Systems, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.
Journal of Neurophysiology
|August 13, 1999
Summary
Motor-unit synchronization contributes to physiological tremor in two distinct frequency bands (1-12 Hz and 15-30 Hz). This synchronization explains a significant portion of tremor, offering new insights into tremor generation.
Area of Science:
- Neuroscience
- Human Physiology
- Biomechanics
Background:
- Physiological tremor is a complex motor output.
- Previous studies identified load-independent components of tremor.
- The precise sources of these tremor components remain incompletely understood.
Purpose of the Study:
- To identify and quantify load-independent rhythmic contributions to physiological tremor.
- To determine the role of motor-unit synchronization in generating these tremor components.
- To revise the definition of normal physiological tremor based on new findings.
Main Methods:
- Simultaneous recordings of finger tremor acceleration, surface electromyogram (EMG), and motor-unit discharges from the extensor digitorum communis (EDC) muscle.
- Data collected from 13 subjects under unloaded and loaded (5-40g) conditions.
- Frequency domain analysis, Fourier-based population analysis, and multivariate analysis were employed.
Main Results:
- Two distinct frequency bands of motor-unit synchronization were identified: 1-12 Hz and 15-30 Hz.
- These synchronization components were present across different loading conditions and were not related to motor-unit firing rates.
- Motor-unit synchronization accounted for an average of 20% of the total physiological tremor signal in these frequency bands.
Conclusions:
- Motor-unit synchronization is a significant source of load-independent rhythmic contributions to normal physiological tremor.
- Normal physiological tremor is a complex signal reflecting motor-unit synchronization across specific frequency bands.
- A revised definition of physiological tremor should incorporate tremor spectra and motor-unit activity correlations.
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