Semmler J G, Nordstrom M A
Department of Physiology, University of Adelaide, Australia.
Exp Brain Res. 1995;104(1):115-25. doi: 10.1007/BF00229861.
Discharge properties of motor units (MUs) in the first dorsal interosseous muscle (FDI) were studied in the dominant and non-dominant hands of six right-handed (RH) and six left-handed (LH) individuals. MU discharge rates and variability were similar in each hand in RH (186 MUs) and LH (160 MUs) subjects. MU synchronization was less prominent in the dominant hand of RH subjects, with 51% (45/88) of cross-correlograms of MU discharge having significant central peaks, compared with 81% (90/111) for the non-dominant hand. The strength of MU synchronization (expressed as the frequency of extra synchronous discharges above chance) was weaker in the dominant hand of right-handers (0.23 +/- 0.03 s-1 vs 0.39 +/- 0.03 s-1), and synchronous peaks from that hand were slightly broader. Four of six RH subjects had significant differences in synchronization between hands (weaker in dominant hand). In contrast, left-handers had similar incidence (80 vs 82%, n = 161) and strength (0.41 +/- 0.03 s-1 vs 0.37 +/- 0.03 s-1) of MU synchrony in dominant and non-dominant hands. No LH subject had a significant difference in synchronization between hands. Force tremor was quantified in each hand in the same subjects during isometric abduction of FDI at 0.5 N and 3.5 N, and directly correlated with the extent of MU synchronization in the muscle. Tremor root mean square amplitude was similar in dominant and non-dominant hands. Power spectral analysis of the tremor force revealed that the peak frequency in the power spectrum was not influenced by handedness, but power at the peak frequency was higher in the non-dominant hand of RH subjects. Correlations between MU discharge variability and synchrony with measures of tremor amplitude were weak. The reduced MU synchronization in the dominant hand of right-handers may reflect a more restricted distribution of direct projections from motor cortical neurons within the FDI motoneuron pool, or reduced excitability of the cortical neurons during the task. These differences in MU synchronization, however, had an insignificant influence on the magnitude of physiological tremor in the FDI.
在六名右利手（RH）和六名左利手（LH）个体的优势手和非优势手中，研究了第一背侧骨间肌（FDI）运动单位（MU）的放电特性。RH组（186个运动单位）和LH组（160个运动单位）受试者每只手的运动单位放电率和变异性相似。RH受试者优势手中的运动单位同步性不太明显，运动单位放电的互相关图中有51%（45/88）具有显著的中心峰值，而非优势手为81%（90/111）。右利手优势手的运动单位同步强度（以高于偶然水平的额外同步放电频率表示）较弱（0.23±0.03 s-1对0.39±0.03 s-1），且该手的同步峰值稍宽。六名RH受试者中有四名双手同步性存在显著差异（优势手较弱）。相比之下，左利手优势手和非优势手的运动单位同步发生率（80%对82%，n = 161）和强度（0.41±0.03 s-1对0.37±0.03 s-1）相似。没有LH受试者双手同步性存在显著差异。在相同受试者的每只手中，在FDI等长外展至0.5 N和3.5 N时对力量震颤进行了量化，并且与肌肉中运动单位同步程度直接相关。震颤均方根振幅在优势手和非优势手中相似。对震颤力的功率谱分析表明，功率谱中的峰值频率不受利手影响，但RH受试者非优势手在峰值频率处的功率更高。运动单位放电变异性和同步性与震颤幅度测量值之间的相关性较弱。右利手优势手中运动单位同步性降低可能反映了FDI运动神经元池内运动皮层神经元直接投射的分布更受限，或者在任务期间皮层神经元的兴奋性降低。然而，这些运动单位同步性的差异对FDI中生理性震颤的幅度影响不显著。
