To understand neuronal circuits concerning motor skill learning we built a wheel running system in which mice learn stepping-patterns. This motor learning system consists of a wheel turning at a constant speed with pegs on which mice run. The mice deprived of water in their home cages were trained to keep running on the pegs to drink water from a spout. When the peg-pattern was changed from a complicated pattern to another, the mice are required to adjust their stepping-pattern to the new peg-pattern. Using this system we reported that mice could learn these complicated stepping–patterns and c-Fos expression was increased in the motor cortices and the dorsolateral striatum on the day of stepping-pattern learning (264.8, 32nd SfN meeting, 2002). In this study, we investigated what type(s) of neuronal inputs to the striatum was activated by the peg-pattern change. We injected DiI into the dorsolateral striatum, and examined c-Fos expression in retrogradely labeled neurons. DiI labeled neurons were found in t...