history of major systemic illness, including uncontrolled hypertension, diabetes, chronic renal insufficiency, autoimmune diseases or malignancies

history of neurological disorders which might affect sensation such as previous stroke or peripheral neuropathy

history of substance abuse (except painkillers)

heavy smokers (with a daily consumption \>20 cigarettes)

pregnancy or lactation

any contraindication for magnetic resonance imaging (MRI)

and any obvious infection or inflammation over a period of at least 1 month before the study.

Neurologic Signatures of Chronic Pain Disorders