Stress-induced Scratching in Healthy and AD

Inclusion Criteria: 1. Healthy subjects and AD patients between 18 and 59 years of age. 2. Healthy subjects: In general, good health without history of neurological and psychiatric diseases. 3. AD patients: An average itch rating of 3 out of 10 or greater in the past two weeks using a Numerical Rating Scale (NRS). 4. All patients will be required to cease use of oral antihistamines from the night before each study visit until the end of the experiment. The purpose is to avoid that participants fall asleep during MRI measurement due to side effect oral antihistamine (i.e., sedation). 5. Women of child bearing potential will be administered a pregnancy test to verify that they are not pregnant. 6. MRI Compatibility, criteria include having no major contraindication for MRI (pacemaker, vascular stents, metallic ear tubes, and absence of metal implants or braces) as assessed by MRI technologist using site approved screening form. 7. Participants have to be able to speak and read English fluently. 8. Participants must have signed a written informed consent before being enrolled in the study Exclusion Criteria: 1. Individuals under 18 or over 59 years of age. 2. Inability to complete the required measures. 3. Suffering from any disease state or physical condition, which would increase their health risk by study participation. 4. Currently enrolled in any investigational study in which the subject is receiving any type of drug, biological, or non-drug therapy. 5. Recent initiation (within last 3 months) of centrally acting agents such as antidepressants, neuroleptics or neuropathic medications. 6. Patients who use centrally acting agents only when they need. The purpose is to avoid a risk of acute effect of these agents on brain activity and perceived stress due to the stress task. 7. Current treatment with opioid analgesics. 8. Uncontrolled thyroid disease. 9. Use of illicit drugs or history of opiate addiction. 10. Diagnosis of a major psychiatric disorder such as schizophrenia, major depression or bipolar disorder that is active right now. 11. Any known diseases or disorders that may affect conducting the experiments (e.g., intracranial pathology, claustrophobia, severe respiratory or cardiovascular problems, active fibromyalgia) or diseases that have potential risks of infections (e.g., HIV, Hepatitis C, etc). 12. Inability to speak and read English. 13. Being pregnant. 14. Incarcerated.