Figure 1.

Effort-benefit reaching task and modulation of monkeys’ performance. (A) Timeline of the standard instrumental paradigm. A visual instruction cue was presented briefly after the animal moved the hand-controlled cursor (+) to the start position. After random delays, a target was presented (second gray circle), and then the start position was extinguished (go signal), at which time the animal was required to move the cursor to the target position. At a random delay after successful target capture, reward was delivered. (B) The instruction cue presented on a single trial was selected pseudo-randomly from 9 possible visually distinct cues. The cues were associated with different levels of reward (3 quantities of food) and effort (3 different friction loads opposing movement). (C) Measures of performance were averaged (mean ± SEM) separately for each reward/effort combination across all recording sessions (81 and 26 sessions for monkeys C and H, respectively). Reaction times and movement accelerations were affected by both expected reward value (***P<0.001, two-way ANOVA) and force level (##P<0.01, ###P<0.001, two-way ANOVA). Gray lines show the reward-related effects.