Skilled forelimb movements and internal copy motor circuits

•Refinement of forelimb movement is thought to rely on forward model predictions.•Forward models use internal copies of motor commands to predict movement outcome.•Internal copy-based predictions can support online correction and adaptation of limb movements.•Mouse genetic tools are helping to resolve neural substrates of internal copy pathways.

Mammalian skilled forelimb movements are remarkable in their precision, a feature that emerges from the continuous adjustment of motor output. Here we discuss recent progress in bridging the gap between theory and neural implementation in understanding the basis of forelimb motor refinement. One influential theory is that feedback from internal copy motor pathways enables fast prediction, through a forward model of the limb, an idea supported by behavioral studies that have explored how forelimb movements are corrected online and can adapt to changing conditions. In parallel, neural substrates of forelimb internal copy pathways are coming into clearer focus, in part through the use of genetically tractable animal models to isolate spinal and cerebellar circuits and explore their contributions to movement.