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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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Correlations between the pool-averaged coherence levels at tremor frequency and the tremor amplitudes in shoulder and elbow joints. Exponential regression results show that the tremor amplitudes in DOFs of a elbow flexion, c shoulder abduction, and d shoulder rotation are significantly correlated with the pool-averaged coherence level at tremor frequency, while that of b shoulder flexion isn’t. Different subjects are indicated with different markers and the error bars indicate the standard deviation of tremor amplitudes of each subject
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Fig7: Correlations between the pool-averaged coherence levels at tremor frequency and the tremor amplitudes in shoulder and elbow joints. Exponential regression results show that the tremor amplitudes in DOFs of a elbow flexion, c shoulder abduction, and d shoulder rotation are significantly correlated with the pool-averaged coherence level at tremor frequency, while that of b shoulder flexion isn’t. Different subjects are indicated with different markers and the error bars indicate the standard deviation of tremor amplitudes of each subject

Mentions: The relationships between pool-averaged coherence levels and tremor amplitudes in joint DOFs were characterized at tremor frequency and double tremor frequency using linear regression, shown in Figs. 7 and 8 respectively. At tremor frequency, the pool-averaged coherence level is significantly correlated with tremor amplitudes in elbow flexion (Fig. 7a), shoulder abduction (Fig. 7c), and shoulder rotation (Fig. 7d) (P < 0.05 and R2 > 0.5), but not significantly correlated with tremor amplitude again in shoulder flexion (Fig. 7b) (P = 0.32, R2 = 0.14). At double tremor frequency, the correlation is weak (P > 0.05, R2 < 0.5) (Fig. 8). The strong correlation at tremor frequency for the pool-averaged coherence is consistent with the fact that paired coherence between muscles displays a stronger component at tremor frequency than at double tremor frequency. Thus, they are sensitive measurements for quantifying the level of inter-muscular synchronization.Fig. 7


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)

Correlations between the pool-averaged coherence levels at tremor frequency and the tremor amplitudes in shoulder and elbow joints. Exponential regression results show that the tremor amplitudes in DOFs of a elbow flexion, c shoulder abduction, and d shoulder rotation are significantly correlated with the pool-averaged coherence level at tremor frequency, while that of b shoulder flexion isn’t. Different subjects are indicated with different markers and the error bars indicate the standard deviation of tremor amplitudes of each subject
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig7: Correlations between the pool-averaged coherence levels at tremor frequency and the tremor amplitudes in shoulder and elbow joints. Exponential regression results show that the tremor amplitudes in DOFs of a elbow flexion, c shoulder abduction, and d shoulder rotation are significantly correlated with the pool-averaged coherence level at tremor frequency, while that of b shoulder flexion isn’t. Different subjects are indicated with different markers and the error bars indicate the standard deviation of tremor amplitudes of each subject
Mentions: The relationships between pool-averaged coherence levels and tremor amplitudes in joint DOFs were characterized at tremor frequency and double tremor frequency using linear regression, shown in Figs. 7 and 8 respectively. At tremor frequency, the pool-averaged coherence level is significantly correlated with tremor amplitudes in elbow flexion (Fig. 7a), shoulder abduction (Fig. 7c), and shoulder rotation (Fig. 7d) (P < 0.05 and R2 > 0.5), but not significantly correlated with tremor amplitude again in shoulder flexion (Fig. 7b) (P = 0.32, R2 = 0.14). At double tremor frequency, the correlation is weak (P > 0.05, R2 < 0.5) (Fig. 8). The strong correlation at tremor frequency for the pool-averaged coherence is consistent with the fact that paired coherence between muscles displays a stronger component at tremor frequency than at double tremor frequency. Thus, they are sensitive measurements for quantifying the level of inter-muscular synchronization.Fig. 7

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