Brain scans reveal how placebo cream eases pain

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Subject must be a volunteer with a minimum age of 18 years and must be able and willing to provide written informed consent. * If female, the subject must be non-lactating, not pregnant, and using a reliable contraception method. * Subject must be able to read and speak English. * Subject must be able to understand and follow the instructions of the investigator and understand all screening questionnaires. * Subject must have no current or recent history of pathological pain. * Subject must have abstained from alcohol and substance use for 48 hours. * Subject must pass all fMRI screening tests. Exclusion Criteria: * If female, pregnancy. * Inability to tolerate the scanning procedures (e.g., claustrophobia). * Metal in body or prior history working with metal fragments (e.g., as a machinist). * Inability to tolerate heat pain applied to the forearm. * Reporting temporary abnormal levels of pain. * Allergic response to the exfoliating cream. * Current presence of pain. * Current or past history of psychoactive substance abuse or dependence. * Dementias. * Movement disorders except familial tremor. * CNS infection. * CNS vasculitis. * Inflammatory disease or autoimmune disease. * CNS demyelinating disease (e.g. multiple sclerosis). * Space occupying lesions (mass lesions, tumors). * Congenital CNS abnormality (e.g. cerebral palsy). * Seizure disorder. * History of closed head trauma with loss of consciousness. * History of cerebrovascular disease (stroke, TIAs). * Abnormal MRI (except changes accounted for by technical factors or UBOs. * Neuroendocrine disorders (e.g., Cushings disease). * Uncorrected hypothyroidism or hyperthyroidism. * Current or past history of cancer. * Recent history (within two years) of myocardial infarction, severe cardiovascular disease, or currently active cardiovascular disease (e.g. angina, cardiomyopathy). * Uncontrolled hypertension or hypotension. * Chronic pain syndromes. * Chronic fatigue syndromes. * A history of neurologic disease or neuropathic pain. * Prior treatment within the last month with any of the following: antidepressants, mood stabilizers, glucocorticoids, opiates. * Prior treatment with any of the following: antipsychotics, isoniazid, centrally active antihypertensive drugs (e.g. clonidine, reserpine). * Any other contraindications for MRI examination (e.g., metallic implants such as pacemakers, surgical aneurysm clips, or known metal fragments embedded in the body). * Current treatment for psychiatric disorders including mood, anxiety, substance abuse, attention-deficit/hyperactivity disorder (ADHD), psychosis. * Neurological disorders (e.g., taking dopamine agonists for Parkinson's) Cardiovascular disease or medication (e.g., taking ACE (angiotensin-converting-enzyme) inhibitors for cardiac remodeling). * Frequent smoking (\> 5 cigarettes / day). * Frequent alcohol use (\> 14 drinks / week). * Frequent migraines (\> 5 / month on average).