Fig. 1.

Experimental setup. A: diagram showing the visual display presented to all subjects during testing of unilateral and bilateral isometric index finger forces. Subjects were instructed on a monitor to perform 10% of left maximal isometric index finger abduction (10% ABD), whereas the right index finger remained at rest (0% Rest) or performed 30% of maximal isometric index finger abduction (30% ABD) or adduction (30% ADD) while motor evoked potentials (MEPs), interhemipheric inhibition (IHI), and short-interval intracortical inhibition (SICI) were tested in the left index finger. The condition in which the right hand remained at rest was used as baseline. The black vertical bar is the cursor that subjects were instructed to move by performing left and right isometric forces. The “GO” signal (gray box located to the left or to the right of the cursor) was the target to which subjects had to move the cursor. The distance between cursor and target is related to the magnitude of force required to accomplish each task, normalized to the maximal voluntary effort determined in each participant. B: schematic of the experimental setup showing the posture of both hands during testing. The left hand was always positioned in prone posture (palm down), whereas the right hand was positioned in prone or supine (palm up) posture. Then, when the right index finger performed ABD in the prone position the first dorsal interosseous (FDI) muscle was acting as an agonist to the task, whereas when the right index finger performed ABD in the supine position the FDI muscle was acting as an antagonist to the task.