S182. Visual inputs control of sustained muscle contraction

Autor: Giuseppe Lucente, Jaume Coll Canti, Josep Valls-Solé
Rok vydání: 2018
Předmět:
Zdroj: Clinical Neurophysiology. 129:e210
ISSN: 1388-2457
DOI: 10.1016/j.clinph.2018.04.542
Popis: Introduction Very few is known about visual influences on volitional motor control. It is speculated that visual attention mediated by the dorsal stream might play an important role in motor planning in grasping and reaching tasks while little is known about the influence of visual inputs on motor control. The cortical silent period (cSP) to transcranial magnetic stimulation (TMS) is a measure of cortical motor inhibition that is strongly related to the degree of muscular activation. We aimed at investigating the effect of alteration of visual inputs on the descending control of muscle activation during a sustained contraction in healthy subjects by measuring the relationship between cSP duration and the level of electromyographic (EMG) activity on a target muscle. Methods We obtained motor evoked potential (MEP) and cSP to TMS at a stimulus intensity of 130% of resting motor threshold while subjects were maintaining a unilateral first dorsal interosseous (FDI) muscle contraction. In the control condition, subjects had their two hands visible on a convenient table. In the test condition, the hand under examination was hidden from the subject’s view inside a custom-made box that had a mirror reflecting the contralateral (inactive) hand. Subjects were instructed to maintain the same amount of muscle contraction in the two conditions, of about 30% of their maximum. We recorded 5 trials for each condition and calculated the average value for MEP onset latency, MEP peak-to-peak amplitude, MEP termination and CSP duration (from stimulus artefact to the moment in which any EMG activity resumed after inhibition). Subjects were not aware of the aims of the study. They were only instructed on generating and maintaining the same voluntary strength of the FDI contraction in the two conditions. We performed a Wilcoxon non-parametric test for related variables, comparing control and test conditions. Statistical significance was set to two-tailed p Results Fifteen healthy subjects were included (mean age 29.6 ± 4.6 years, F 74%, right handedness 98.1%). Mean MEP onset latency (24.1 ± 2.2 ms vs 23.9 ± 2.1 ms) and peak-to-peak amplitude (2.3 ± 0.9 mV vs 2.5 ± 0.6 mV) were not significantly different in the two study conditions (p > 0.05 for the two comparisons). However, CSP duration shortened significantly when subjects had their hand out of their view (114.4 ± 9.7 ms vs 83.6 ± 9.3 ms p = 0.004). A trend of an increased background EMG activity was found in the test condition with respect to baseline, although not statistically significant (706 ± 488 uV vs 1074 ± 804 uV p = 0.1). Conclusion Visual inputs contribute to modulate descending control of force during a sustained muscle contraction. In our case, it is possible that vision of an inactive hand when trying to keep a sustained contraction might have modified corticospinal output in a way that inhibition was diminished.
Databáze: OpenAIRE
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