I am putting the links here, so they do not get buried in that question and all the responses under the "Dopamine" question.
1. "Excitability of Spinal Flexor Reflex" ncbi.nlm.nih.gov/pubmed/107...
2. "Reflex Testing Reveals Circadian variation of Spinal Excitability in RLS Patients"
3. "Electrophysiology in RLS" mdvu.org/emove/article.asp?...
Those are 3 links to what I was saying about spinal chord excitability in people with RLS, which is found through reflex tests and sleep studies.
These will get you started. In my search engine I put "spinal chord excitability RLS ". All these links and many, many more will pop up. I have more, but on my old computer which is not accessible at this time.