Inclusion Criteria:

• Subject selections will be equitable among those individuals who meet the inclusion criteria. Every effort will be made to balance gender and race. In order to be eligible to participate in this study, an individual must meet all of the following criteria:
• * Ability of subject to understand and the willingness to sign a written informed consent document.
• * Males and females; Age 18 to 55.
• * Able to read and write in English to guarantee understanding of all written and spoken instructions, which are in English.

Exclusion Criteria:

• An individual who meets any of the following criteria will be excluded from participation in this study:
• For all experiments:
• * Unable to comply with study procedures or follow-up visits
• * Has any serious or unstable medical condition or history that in a clinician s assessment implies a cardiovascular, neurological, or physical risk from the study procedures performed to induce negative valence states. This may include chronic systemic disorders that could worsen due to stress (e.g. uncontrolled hypertension, coronary artery disease for example a history of myocardial infarction or stable or unstable angina, or diabetes)
• * Has any current psychiatric diagnosis (based on SCID) or no diagnosis but scores \>=29 on Beck Depression Inventory II or \>=26 on Beck Anxiety Inventory
• * Meets criteria for diagnosis of any substance-related or addictive disorder, or endorses any kind of problematic gambling behavior or problematic media-based addictive behavior (such as videogames, social-networking, online shopping, etc.)
• * Regular use of psychoactive medications or psychoactive substances
• * Regular use of corticosteroids
• * Is pregnant
• * NIMH employees and staff and their immediate family members
• For stress and pain induction:
• * Has a major medical condition or medical history that in a clinician s assessment could affect temperature sensitivity, pain thresholds, or ability to comply with study procedures. This may include cardiovascular, autonomic, neurological, psychiatric, or chronic systemic disorders (including but not limited to stroke, blindness, deafness, history of brain damage, neurodegenerative, neurotoxic or demyelinating disorder, or diabetes)
• * Has a medical condition that in a clinician s assessment might affect somatosensation (e.g., Raynaud s disease, peripheral neuropathy, or circulatory disorder)
• For pain induction:
• * Has a current chronic pain condition or has had chronic pain in the past (painful condition lasting more than six months)
• * Has a dermatological condition such as scars or burns, or has had a tattoo in the testing region within the previous 4 weeks that might influence cutaneous sensibility
• * Regular and recent use of prescription or over-the-counter medication that has a significant effect on pain or heat perception. These include medications such as centralacting agents such as opiates (morphine, tramadol), antidepressants (amitriptyline, duloxetine, milnacipran), anticonvulsants (gabapentin, pregabalin), anxiolytics (barbiturates, benzodiazepines), hypnotics (zolpidem, sodium oxybate), antipsychotics (valproate, lithium, olanzapine), antimigraine agents (sumatriptan, ergotamine), and muscle relaxants (cyclobenzaprine, carisoprodol). Use of analgesic medications, such as non-steroidal anti-inflammatories, salicylates, and acetaminophen, taken on an as needed basis is acceptable as long as the last dose taken was within 5 half-lives of testing.
• For craving induction:
• * Has a condition that in a clinician s assessment could preclude the ability to hold 4-6 hours of fasting or that is associated with a risk of hypoglycemia (such as diabetes, kidney disease, insulinoma, adrenal or pituitary tumors or disorders, or anorexia nervosa)
• * Is currently engaged in any kind of diet medically- or self-prescribed or endorses a very strong desire to start a diet that involves eliminating or decreasing carbohydrate consumption
• * Has a history of food allergies such as tree-nut or peanut allergy.
• For fMRI experiments:
• * Individuals with conditions that could pose a risk relating to the safety of the fMRI procedure but do not meet specific exclusion criteria for all experiments or for specific inductions will be excluded from the MRI portion of the protocol but may participate in the non-MRI sessions. Such conditions include:
• * Those with ferromagnetic metal in the cranial cavity or eye (e.g. aneurysm clip, implanted neural stimulator, cochlear implant, ocular foreign body)
• * Those with an abnormality on a structural MRI
• * Those with an implanted cardiac pacemaker or auto-defibrillator
• * Those with an insulin pump
• * Those with an irremovable body piercing
• * Pregnancy (based on urine test completed within 24 hours prior to scan)
• * Left-handed (only for fMRI experiments involving thermal pain stimulation)