What part of the brain modifies the activity of upper motor neurons to produce voluntary movements and inhibit involuntary ones?

The part of the brain is known as the basal nuclei.

Explanation:

This structure is a set of subcortical nuceli, located on either side of the thalamus, around the same height as the temporal lobe.

They have different functions:

Planning, integration and execution of any voluntary movement, as well as the inhibition of any involuntary movements. Procedimental learning: learning an action and being able to carry it out without thinking too much about it, such as driving. Executive functions: planning, cognitive thinking, problem solving, amongst others. They play a role in motivational and emotional conduct.