Sensorimotor feedback loops are selectively sensitive to reward

While it is well established that motivational factors such as earning more money for performing well improve motor performance, how the motor system implements this improvement remains unclear. For instance, feedback-based control, which uses sensory feedback from the body to correct for errors in movement, improves with greater reward. But feedback control encompasses many feedback loops with diverse characteristics such as the brain regions involved and their response time. Which specific loops drive these performance improvements with reward is unknown, even though their diversity makes it unlikely that they are contributing uniformly. This lack of mechanistic insight leads to practical limitations in applications using reward, such as clinical rehabilitation, athletic coaching, and brain-inspired robotics. We systematically tested the effect of reward on the latency (how long for a corrective response to arise?) and gain (how large is the corrective response?) of eight distinct sensorimotor feedback loops in humans. Only the feedback responses known to rely on prefrontal associative cortices showed sensitivity to reward, while feedback responses that relied mainly on premotor and sensorimotor cortex did not show sensitivity to reward. Our results may have implications regarding feedback control performance in pathologies showing a cognitive decline, or on athletic coaching. For instance, coaching methodologies that rely on reinforcement or "reward shaping" may need to specifically target aspects of movement that rely on reward-sensitive feedback responses.