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Long‐range correlations in motor unit discharge times at low forces are modulated by visual gain and age
Author(s) -
Jordan Kimberlee,
Jesunathadas Mark,
Sarchet Derek M.,
Enoka Roger M.
Publication year - 2013
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2012.067975
Subject(s) - motor unit , range (aeronautics) , physics , audiology , psychology , medicine , materials science , neuroscience , composite material
New findings• What is the central question of this study? Changes in visual gain do not influence the time‐dependent structure of motor unit discharge variability in young adults; however, the influence of visual gain on the regularity of motor unit discharge times in old adults is unknown. • What is the main finding and its importance? We examined the association between visual information and the size and temporal structure of the variability in index finger force and motor unit discharge times when young and old adults performed isometric contractions with a hand muscle. We showed that the regularity with which motor units discharged action potentials decreased with increased gain of visual feedback, regardless of age.The purpose of this investigation was to examine the association between visual information and the size and temporal structure of the variability in index finger force and motor unit discharge times when young and old adults performed isometric contractions with a hand muscle. Single motor units ( n = 32) in the first dorsal interosseus muscle were recorded as subjects [16 young (18–35 years old) and 16 old (≥70 years old)] exerted a constant abduction force with the index finger during 60 s isometric contractions. The target force was displayed on a monitor in front of the subjects, and they were asked to match the index finger force to a target force. The amount of visual feedback, or gain of the signal, was varied between 24 (low gain) and 1175 pixels N −1 (high gain). In addition, some trials were performed in the absence of visual feedback. The dependent variables were the variability (standard deviation and coefficient of variation) and the regularity (detrended fluctuation analysis self‐similarity parameter, α) of motor unit discharge times and the abduction force. Motor unit discharge times became less regular with an increase in visual feedback gain for both young and old adults, whereas motor unit discharge variability was not influenced by changes in visual gain. The regularity of motor unit discharge times was less for old adults than for young adults, but the variability was greater for old adults. However, there was a significant association between the regularity of motor unit discharge times and the regularity of force for the old adults, but not the young adults. These observations suggest that adjustments in the synaptic inputs delivered to motor neurons with changes in the visual gain differed for young and old adults.