Effects of a Cocoa Shot on the Human Brain

Inclusion Criteria: * Consume 200-600 mg caffeine daily * Willing and capable of signing the informed consent * Willing to attend 4 testing sessions that will take 4-6 hours each AND will be at least 7 days apart * Willing to abstain from caffeine for 24 hours before each testing session * Willing to and able to have MRIs Exclusion Criteria: * As determined from the medical screening session * active neurological dysfunction (such as a major Axis I psychopathology, Alzheimer's disease, Parkinson's disease, prior history of stroke, epilepsy, or serious central nervous system (CNS) trauma) * attention deficit hyperactivity disorder (ADHD) * migraines * hypertension * diabetes * peripheral vascular disease * taking vasoactive medications (such as anti-hypertensive medications) * depression that has not been on a stable medical treatment for at least 4 weeks * Pregnancy * Color blindness * Allergy to chocolate, peanuts, tree nuts, egg, soy, mike, wheat * Individuals who are or potentially may be cognitively or psychologically impaired, or who otherwise have a limited capacity to provide consent