What is the central question of this study? When performing skillful hand movement, motor command descends especially toward distal arm muscles. Does central command evoke a vascular response selectively in the distal arm muscles during skillful hand movement? What is the main finding and its importance? We found using near-infrared spectroscopy that unilateral skillful hand movement evoked a greater increase in oxygenation of the contralateral forearm muscle as compared to that of the upper arm muscles. Mental imagery of the hand movement also increased oxygenation of the forearm muscle. These findings suggest that central command may contribute to the vasodilator response in the non-contracting forearm muscle during contralateral skillful hand movement. Abstract The human hand is a special organ to perform skillful movement in daily life. To meet metabolic demands of the working distal arm muscles, central command may evoke neurogenic vasodilation in the muscles. Based on our previous finding demonstrating that centrally-generated vasodilator signal is transmitted bilaterally to skeletal muscles during exercise, the centrally-induced vasodilation may occur in the non-contracting distal arm muscles during contralateral skillful hand movement. To examine the possibility, we measured using near-infrared spectroscopy the relative concentrations of oxygenated-haemoglobin (Oxy-Hb, as an index of regional blood flow) in the non-contracting arm muscles during skillful hand movement (two-ball rotation) in 22 subjects. Two-ball rotation increased Oxy-Hb of both forearm and upper arm muscles with little changes in perfusion pressure and cardiac output. The increased Oxy-Hb was greater in the forearm muscle than the upper arm muscles. The increased Oxy-Hb of the forearm muscle during two-ball rotation was greater than that during one-armed cranking performed with no load. Mental imagery of two-ball rotation increased Oxy-Hb of the forearm and biceps muscles. The increases in Oxy-Hb of both forearm and upper arm muscles during two-ball rotation were reduced by decreasing the level of task difficulty. Intravenous administration of atropine attenuated the increases in Oxy-Hb of the arm muscles during two-ball rotation. It is likely that contralateral skillful hand movement evokes selective increase in Oxy-Hb of the non-contracting forearm muscle via a sympathetic cholinergic mechanism and that the increase in oxygenation may be at least partly mediated by central command.
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