Evolutionary expansion of the corticospinal system is linked to dexterity in Peromyscus mice

Furthermore, forest mice display greater manual dexterity than their prairie counterparts in a reach-to-grasp task, consistent with the idea that an increase in CSN number supports more dexterous behavior. High-throughput neural recordings during this task revealed a difference in the timing of neural activity between forest and prairie mice, specifically in M2: in forest mice, the peak of activity was shifted towards the grasping phase of the behavior.

Forest mice also outperform their prairie counterparts on an ecologically relevant climbing task, where they spend more time upright crossing a thin rod, move faster, and right themselves more quickly when they fall, suggesting a general difference in motor dexterity not restricted to hand use. Finally, we use F2 hybrid animals to show that CST size is correlated with climbing dexterity, providing support for the long-standing hypothesis that corticospinal system expansion supports the evolution of dexterity.

Together, our work establishes the forest-prairie deer mouse system as a model to investigate the role of neuron number expansion, and CSNs in particular, in dexterous movement.