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Extraction of the EPP Component from the Surface EMG
Published on: December 17, 2009
Abnormal corticomuscular and intermuscular coupling in high-frequency rhythmic myoclonus
P Grosse1, R Guerrini, L Parmeggiani
1Sobell Department of Clinical Neurophysiology, Institute of Neurology, London, UK. p.grosse@ion.ucl.ac.uk
Brain : a Journal of Neurology
|January 23, 2003
Summary
Frequency analysis of electroencephalogram (EEG)-electromyogram (EMG) and EMG-EMG coherence offers advantages over back-averaging for assessing cortical myoclonus. This method reveals distinct physiological coupling differences between proximal and distal muscles in affected patients.
Area of Science:
- Neurophysiology
- Clinical Electrophysiology
- Movement Disorders
Background:
- Cortical myoclonus is characterized by high-frequency, rhythmic myoclonic electromyogram (EMG) bursts.
- Frequency analysis may offer advantages over back-averaging for neurophysiological assessment.
- The clinical utility and physiological basis of EEG-EMG and EMG-EMG coherence in cortical myoclonus are not fully established.
Purpose of the Study:
- To investigate EEG-EMG and EMG-EMG coupling in proximal and distal upper limb muscles in patients with high-frequency rhythmic myoclonus.
- To compare the sensitivity of frequency analysis techniques with back-averaging.
- To elucidate the physiological systems contributing to coherence in cortical myoclonus.
Main Methods:
- Studied nine patients with multifocal, high-frequency rhythmic myoclonus.
- Utilized frequency analysis to assess EEG-EMG and EMG-EMG coherence in proximal and distal upper limb muscles.
- Compared findings with back-averaging techniques.
Main Results:
- Exaggerated coherence was observed between electroencephalogram (EEG) and contralateral electromyogram (EMG), and between ipsilateral EMG pairs.
- Frequency analysis of EMG-EMG mirrored EEG-EMG results, with EMG-EMG superior for detecting exaggerated common drive in distal muscles.
- Both frequency analysis techniques were more sensitive than back-averaging and revealed distinct proximal vs. distal muscle coupling patterns.
Conclusions:
- Functional coupling between cortex and distal muscles in cortical myoclonus is dominated by efferent processes.
- Coupling in proximal muscles shows inter-individual variability, reflecting both afferent and efferent loops.
- The physiological mechanisms underlying myoclonic discharges differ between proximal and distal muscles and vary among patients.
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