||Differential tremor dynamics of concurrent pointing tasks on level surface and balance plate
||Department of Physical Therapy
Round balance plate
Principal component analysis
研究結果: 相較於穩定平面站立，在圓托平衡板上站立時，身體肢段的生理震顫強度顯著增加，在上臂和下肢的部份尤其明顯。從鄰近肢段的震顫訊號相關性顯示出：相較於平面站立情況，在圓托平衡板上站立時，肢段間的震顫耦合程度有明顯的協調；在上肢部份增加肢段間的耦合強度，而降低下肢的耦合強度，特別在足踝關節兩端與上臂-腰椎間的震顫耦合程度降低。隨著站立平面變得不穩定，下肢震顫近似熵降低代表震顫訊號的規律性有特別增加的趨勢。經主成份分析與共通性變化，本研究發現：相較於平面站立，圓托平衡板站立的第一震顫主成份的變化主要來自下肢，明顯地出現1-4 Hz頻帶範圍的尖峰；第二震顫主成份主要來自上肢震顫，其1-4 Hz 和8-13 Hz兩個頻帶範圍的頻譜功率都有顯著的上升。在圓托平衡板站立下，食指低頻晃動與站立平面低頻晃動之比值遠較穩定平面站立情形為小，顯示受試者在圓托平衡板站立下，能採取有效之關節協調策略，減少低頻晃動的傳導。
結論: 本研究由姿勢性震顫特徵改變發現，在維持姿勢指向動作時，身體的協調控制策略會因應站立平面的穩定程度而改變: 在圓托平衡板上站立時，受試者注意力轉移至下肢，藉由踝關節與軀幹的調節以適應平衡板產生的搖晃，並減少上肢關節在指向作業的活動自由度，同時達到指向準確與站立平衡的雙重目標；動態姿勢協調的神經證據經由震顫主成份特徵而加以深入討論。
Objective: Through interplay of multi-segment postural tremors, the aim of this study was to investigate the variations in coordinative control of postural pointing on two stance surfaces of different stability levels.
Methods: Twenty healthy volunteers were recruited to participate in this study. They performed a postural pointing task on two different stance surfaces, level surface (LS) and round balance plate (RBP); meanwhile, eight accelerometers were placed on limbs segments, including right index finger, hand, forearm, arm, lumbar, thigh, calf and foot, to record physiological tremors in the anterior-posterior and upward-downward directions during the postural-suprapostural tasks. Besides, low-frequency movement fluctuations (≦1 Hz) of the stance surface and pointing index were recorded with an accelerometer and a laser detector. The intensity of physiological tremors and movement fluctuations of the stance surface and index finger were represented with values of root mean square (RMS). Regularity of segment tremors and tremor coupling between adjacent segments were quantified with approximate entropy and partial correlation with the effect of stance fluctuation removed. Principal component analysis (PCA) and communality analysis were statistical approaches to feature the most important element of physiological tremors, pertaining to coordinative control of the two stance conditions.
Results: Compared with LS stance, RBP stance resulted in significantly greater RMS of physiological tremors, particularly in the arm segment and the lower limb. A general enhancement of tremor coupling was noted in the upper limb but a remarked uncoupling in arm-lumbar and calf-foot complexes. Seesaw stance in the RBP condition also led to a greater regularity in segment tremors of the lower limb. The major differences in the two stances lie in primary principal components (TPC1) and secondary principal component (TPC2) that had relatively higher communality with segment tremors in the lower and upper limbs, respectively. TPC1 in the RBP condition exhibited a prominent 1-4 Hz spectral peak that was absent for TPC1 in the LS condition. Seesaw stance also added to 1-4 Hz and 8-13 Hz spectral amplitudes of the TPC2 in the RBP condition. As the ratio of movement fluctuation of the index to that stance surface was much smaller in the RBP condition than in the LS condition, the subjects were able to minimize transmission of movement fluctuations across segments in the RBP condition.
Conclusion: Stance-related organization of segment tremors suggested that coordinative strategies to optimal postural pointing were modified to balance challenges. During seesaw stance, the subjects tacitly released coupling of the trunk and ankle joint in adaptation to fluctuation movements of balance plate, but intensified joint stiffness of the upper limb to master redundancy in joint space for pointing task. Potential neural correlates for dynamic regulation of postural sway from tremor principal components are discussed.
List of tables....IX
List of figures...X
Chapter 1. Introduction......................1
Chapter 2. Methods ...........................5
2.1 Subjects and experimental protocol.......5
2.3 Data processing and feature extraction...7
2.4 Statistical analyses.....................9
Chapter 3. Results...........................11
3.1 Amplitude of multi-segment physiological tremors..11
3.2 Couplings and regularity of multi-segment physiological tremors.................................11
3.3 Principal component analysis of physiological tremors .............................................12
3.4 Behavioral data: movement fluctuations of the stance surface and index.....................................14
Chapter 4. Discussion.................................16
4.1. Drastic reduction in relative movement fluctuation for postural pointing during seesaw stance............17
4.2 Stance-dependent tremor organization and coordination strategy in the upper limb............................17
4.3 Tremor restructuring and multi-segmental strategy in the lower limb........................................19
4.4 Stance control of neuromuscular basis revealed by principal component analysis..........................22
Chapter 5. Conclusion.................................25
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