Fig. 1: Paradigm and behavior.

a Three types of trials were pseudo-randomly interleaved in each session. In single-reach (SR) trials, monkeys had to perform memory-guided center-out reach. In double-reach (DR) trials, two targets (a square and a triangle) were presented simultaneously in the cue period, and then extinguished; the monkeys were required to hold the central target for a 400–800 ms memory period until it was turned off (GO signal). Next, monkeys finished reaching both targets in the sequence of the square to the triangle within 700–1200 ms. The triangles were located 120° from the squares in CW or CCW directions. Monkey cartoons were created by Miss Jiayue Li. b Hand trajectories in different conditions are grouped by their 1st/only reach direction from monkey C. Some trajectories are overlapped due to high similarity. No significant difference was found before the end of 1st/only reach (one-way ANOVA, p > 0.05). c Surface electromyography (sEMG) and speed in one typical session. The Pearson correlation coefficient of the speed profile until the first movement end between double reach and single reach was 0.99 ± 0.006 (mean ± sd), and of sEMG of extensor digitorum communis (EDC) was 0.99 ± 0.005 (mean ± sd) for monkey C.