Central Pattern Generators are populations of neurons found in the spinal chord that assist in the creation of rhythmic movements. See "Human spinal locomotor control is based on flexibly organized burst generators" by Danner et al, for a recent publication on the topic. How does the brain-based motor system interact with these pattern generators? Do they operate mostly independently or is there some feedback being communicated? If there is feedback, what type of information is it transmitting?
Descending inputs onto the central pattern generating circuit provide stimulus in the form of neuromodulatory chemicals and synaptic currents (Marder 2012). The leech heartbeat pacemaker and the stomatogastric ganglion in crustaceans are well-studied model systems that show descending input from higher functions.
Specifically, in humans, we are not sure. This type of question is best answered in invertebrates for the time being. In invertebrate electrophysiology, the circuit can be "decentralized," by chemically or physically destroying the inputs from the ascending ganglia. In the stomatogastric ganglion, this results in a less-stable but still very robust central pattern (Hamood et al., 2015).