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Contribution of inter-muscular synchronization in the modulation of tremor intensity in Parkinson's disease.

He X, Hao MZ, Wei M, Xiao Q, Lan N - J Neuroeng Rehabil (2015)

Bottom Line: In each subject, the frequencies of rhythmic firings in upper arm muscles were determined using spectral analysis.The phase shift between synchronized antagonistic muscle pairs was calculated to aid coherence analysis in the muscle pool.Recorded EMG revealed that rhythmic firings were present in most recorded muscles, which were either synchronized to form phase-locked bursting cycles at a subject specific frequency, or unsynchronized with a random phase distribution.

View Article: PubMed Central - PubMed

Affiliation: Institute of Rehabilitation Engineering, Med-X Research Institute and School of Biomedical Engineering, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai, 200030, China.

ABSTRACT

Background: Involuntary central oscillations at single and double tremor frequencies drive the peripheral neuromechanical system of muscles and joints to cause tremor in Parkinson's disease (PD). The central signal of double tremor frequency was found to correlate more directly to individual muscle EMGs (Timmermann et al. 2003). This study is aimed at investigating what central components of oscillation contribute to inter-muscular synchronization in a group of upper extremity muscles during tremor in PD patients.

Methods: 11 idiopathic, tremor dominant PD subjects participated in this study. Joint kinematics during tremor in the upper extremity was recorded along with EMGs of six upper arm muscles using a novel experimental apparatus. The apparatus provided support for the upper extremity on a horizontal surface with reduced friction, so that resting tremor in the arm can be recorded with a MotionMonitor II system. In each subject, the frequencies of rhythmic firings in upper arm muscles were determined using spectral analysis. Paired and pool-averaged coherence analyses of EMGs for the group of muscles were performed to correlate the level of inter-muscular synchronization to tremor amplitudes at shoulder and elbow. The phase shift between synchronized antagonistic muscle pairs was calculated to aid coherence analysis in the muscle pool.

Results: Recorded EMG revealed that rhythmic firings were present in most recorded muscles, which were either synchronized to form phase-locked bursting cycles at a subject specific frequency, or unsynchronized with a random phase distribution. Paired coherence showed a stronger synchronization among a subset of recorded arm muscles at tremor frequency than that at double tremor frequency. Furthermore, the number of synchronized muscles in the arm was positively correlated to tremor amplitudes at elbow and shoulder. Pool-averaged coherence at tremor frequency also showed a better correlation with the amplitude of resting tremor than that of double tremor frequency, indicating that the neuromechanical coupling in peripheral neuromuscular system was stronger at tremor frequency.

Conclusions: Both paired and pool-averaged coherences are more consistent indexes to correlate to tremor intensity in a group of upper extremity muscles of PD patients. The central drive at tremor frequency contributes mainly to synchronize peripheral muscles in the modulation of tremor intensity.

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Related in: MedlinePlus

Coherence analyses for evaluation of inter-muscular synchronization. a The paired coherence between muscles FDS and ED in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. The vertical green lines indicate the subject-specific tremor frequency and double tremor frequency of subject P9. b The pooled coherence of all 15 pairs of muscles among 6 recorded muscles in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. c The pool-averaged coherence of all 15 pairs among 6 recorded muscles in subject P9
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Fig3: Coherence analyses for evaluation of inter-muscular synchronization. a The paired coherence between muscles FDS and ED in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. The vertical green lines indicate the subject-specific tremor frequency and double tremor frequency of subject P9. b The pooled coherence of all 15 pairs of muscles among 6 recorded muscles in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. c The pool-averaged coherence of all 15 pairs among 6 recorded muscles in subject P9

Mentions: where α = 99% resulted in a coherence threshold of 0.68, which was adopted as a criterion to determine if the activities of a pair of muscles were strongly synchronized at the tremor frequency (Fig. 3a). The “tremor frequency” represents the “subject-specific tremor frequency” in here and the following text if no specific modifier is set before it.Fig. 3


Contribution of inter-muscular synchronization in the modulation of tremor intensity in Parkinson's disease.

He X, Hao MZ, Wei M, Xiao Q, Lan N - J Neuroeng Rehabil (2015)

Coherence analyses for evaluation of inter-muscular synchronization. a The paired coherence between muscles FDS and ED in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. The vertical green lines indicate the subject-specific tremor frequency and double tremor frequency of subject P9. b The pooled coherence of all 15 pairs of muscles among 6 recorded muscles in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. c The pool-averaged coherence of all 15 pairs among 6 recorded muscles in subject P9
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4666195&req=5

Fig3: Coherence analyses for evaluation of inter-muscular synchronization. a The paired coherence between muscles FDS and ED in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. The vertical green lines indicate the subject-specific tremor frequency and double tremor frequency of subject P9. b The pooled coherence of all 15 pairs of muscles among 6 recorded muscles in subject P9. The horizontal red line indicates the 99 % upper confidence limit of significant coherence level. c The pool-averaged coherence of all 15 pairs among 6 recorded muscles in subject P9
Mentions: where α = 99% resulted in a coherence threshold of 0.68, which was adopted as a criterion to determine if the activities of a pair of muscles were strongly synchronized at the tremor frequency (Fig. 3a). The “tremor frequency” represents the “subject-specific tremor frequency” in here and the following text if no specific modifier is set before it.Fig. 3

Bottom Line: In each subject, the frequencies of rhythmic firings in upper arm muscles were determined using spectral analysis.The phase shift between synchronized antagonistic muscle pairs was calculated to aid coherence analysis in the muscle pool.Recorded EMG revealed that rhythmic firings were present in most recorded muscles, which were either synchronized to form phase-locked bursting cycles at a subject specific frequency, or unsynchronized with a random phase distribution.

View Article: PubMed Central - PubMed

Affiliation: Institute of Rehabilitation Engineering, Med-X Research Institute and School of Biomedical Engineering, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai, 200030, China.

ABSTRACT

Background: Involuntary central oscillations at single and double tremor frequencies drive the peripheral neuromechanical system of muscles and joints to cause tremor in Parkinson's disease (PD). The central signal of double tremor frequency was found to correlate more directly to individual muscle EMGs (Timmermann et al. 2003). This study is aimed at investigating what central components of oscillation contribute to inter-muscular synchronization in a group of upper extremity muscles during tremor in PD patients.

Methods: 11 idiopathic, tremor dominant PD subjects participated in this study. Joint kinematics during tremor in the upper extremity was recorded along with EMGs of six upper arm muscles using a novel experimental apparatus. The apparatus provided support for the upper extremity on a horizontal surface with reduced friction, so that resting tremor in the arm can be recorded with a MotionMonitor II system. In each subject, the frequencies of rhythmic firings in upper arm muscles were determined using spectral analysis. Paired and pool-averaged coherence analyses of EMGs for the group of muscles were performed to correlate the level of inter-muscular synchronization to tremor amplitudes at shoulder and elbow. The phase shift between synchronized antagonistic muscle pairs was calculated to aid coherence analysis in the muscle pool.

Results: Recorded EMG revealed that rhythmic firings were present in most recorded muscles, which were either synchronized to form phase-locked bursting cycles at a subject specific frequency, or unsynchronized with a random phase distribution. Paired coherence showed a stronger synchronization among a subset of recorded arm muscles at tremor frequency than that at double tremor frequency. Furthermore, the number of synchronized muscles in the arm was positively correlated to tremor amplitudes at elbow and shoulder. Pool-averaged coherence at tremor frequency also showed a better correlation with the amplitude of resting tremor than that of double tremor frequency, indicating that the neuromechanical coupling in peripheral neuromuscular system was stronger at tremor frequency.

Conclusions: Both paired and pool-averaged coherences are more consistent indexes to correlate to tremor intensity in a group of upper extremity muscles of PD patients. The central drive at tremor frequency contributes mainly to synchronize peripheral muscles in the modulation of tremor intensity.

Show MeSH
Related in: MedlinePlus