Here, we show that Ras-ERK signaling is increased in motor cortex following rotarod training in the MECP2-duplication syndrome mouse model of autism, and that the abnormal motor learning and excessive stabilization of clustered dendritic spines previously observed in MECP2-duplication mice can be rescued by pharmacological inhibition of Ras-ERK signaling. The gene discussed is MECP2; the disease is Down syndrome.