Fig 1. Study design.

Panel A. Arm positions used for wrist extension and wrist flexion movements. Right wrist extension executed against gravity: The forearm was pronated and a foam wedge positioned the elbow flexed 30 deg. Right wrist flexion against gravity: The forearm was supinated, with the elbow positioned in 30 degrees of elbow flexion. Each repetition of the motor task was cued by the word “Go” appearing on the screen, and the movement end-point (e.g., full wrist extension) was instructed to be held for 1 sec, after which time the instruction on the screen changed to a fixation figure, and the participant lowered the hand to the start position. Panel B. Blocked data acquisition design, with each movement cued within a given block, for one run of the wrist movement task. The upper part of panel B shows the sequence of rest, instruction, and execution periods. The lower part of panel B shows a detailed subsample of a motor execution series on an expanded time scale. In this subsample, movement events are cued at pseudo-random intervals.