Measurement of stretch-evoked brainstem function using fMRI

Sensorimotor feedback loops are selectively sensitive to reward

Although 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. 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 seven distinct sensorimotor feedback loops in humans. Only the fastest feedback loops were insensitive to reward, and the earliest reward-driven changes were consistently an increase in feedback gains, not a reduction in latency. Rather, a reduction of response latencies only tended to occur in slower feedback loops. These observations were similar across sensory modalities (vision and proprioception). Our results may have implications regarding feedback control performance in 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.

There is a topographic organization in human cortico-pontine connectivity

Of the three largest outputs of the cerebral cortex, two have been extensively studied and mapped. Topographic maps of cortico-thalamic and cortico-striatal functional connectivity in humans are well established. However, for the third largest cerebral output, to the pontine nuclei, which connect the cerebrum to the cerebellum, the existence of such an organized connectivity pattern in humans is unknown. Here, using high-resolution functional MRI and a large sample size, we found a topographically organized pattern of functional connectivity between the human cerebral cortex and pons. Our results indicate a rostral-caudal topography; rostral (frontal) cerebral cortex shows connectivity to the rostral pons, and the more caudal cortical areas (i.e. the sensorimotor cortices) show functional connectivity more caudally in the pons, with the occipital lobe connectivity being most caudal. While prefrontal, sensorimotor and occipital cortices have a connectivity to the medial pontine nuclei, posterior parietal cortex and temporal lobe correlate with lateral pontine nuclei. Topography is sufficiently detailed to identify distinct connectivity for leg, trunk, hand and face areas of the motor cortex. These findings reveal the existence of a topographic organization in human cortico-pontine connectivity and provide the topographic map for future studies of cortico-ponto-cerebellum pathway in a variety of disorders.