Final answer:
The cerebellum is the part of the brain mice primarily use when learning to run on complex wheels, as it is responsible for balance and coordination. (option a is the correct answer).
Step-by-step explanation:
When mice are learning to run on complex wheels, they are primarily using their cerebellum. The cerebellum sits at the base of the brain on top of the brainstem and is responsible for controlling balance and aiding in coordinating movement and learning new motor tasks. This part of the brain is essential for activities requiring fine motor skills and coordination, like the precise movements needed to navigate a complex wheel.
The cerebellum is not responsible for language function, which is localized in the majority of people in the left cerebral hemisphere, nor is it part of the corticospinal pathway like the cerebellar deep white matter. The cerebellum also receives proprioceptive input from the spinal cord, particularly in the vermis region.