Causal Mechanisms of Odor-Guided Behavior in Humans

Background: Little is known about how different regions of the brain responsible for the human sense of smell guide behaviors. In this study, researchers use a technique called transcranial ultrasound stimulation (TUS) to learn how odors affect the brain and behavior. Objective: To learn more about how the human sense of smell works. Eligibility: Healthy people aged 18 to 45 years who are right-handed. Design: Participants can volunteer for up to 2 different experiments. Each experiment requires 5 visits, each about 1 week apart. Food, alcohol, and caffeine may be limited before visits. At the start of each visit, participants will answer questions about their health and how well they slept. Their sense of smell will be assessed. Some visits may include tasks on a computer: While doing these tasks, participants may be asked to smell different odors, look at pictures, and listen to sounds. They will wear devices to track breathing, blood pressure, pulse, and other body responses to the tasks. Some visits may include TUS: TUS uses ultrasound waves to briefly change brain activity. A gel will be applied to the scalp and hair, and a device will be placed against the participant s head. Participants may feel a tapping, pulling, and/or warm sensation on the skin underneath the device. They may also feel a twitch in their face, neck, arm, or leg muscles. Participants will do tasks before and after TUS. Some visits will include functional magnetic resonance imaging (fMRI) scans. fMRI uses magnet and radio waves to capture images of the activity inside the brain. Participants will lie on a table that slides into a tube. They will perform tasks inside the scanner.