The total time required for each participant is 4 visits, as outlined below:
Visit 1: Screening, Questionnaires, and Orientation: During this visit potential participants will learn about the study procedures, sign the informed consent documents, complete diagnostic evaluations and medical screening with study staff. Participants will also complete a series of forms that ask about demographic information, OCD symptoms, use of drugs and alcohol, and other aspects of physical and mental health.
Visit 2: Behavioral Tests: During this visit participants will complete several computer tasks. Study staff will measure reaction time and obtain psychophysiological information (e.g., skin conductance recordings). The tasks that the participant completes will involve viewing images within a virtual environment. An aversive stimulus (e.g., loud burst of noise, animated snake) may follow one image most of the time, while other images may never be followed by a noise or a snake. The participant will need to try to predict whether the aversive cue will occur or not based on which image is shown, and will be asked to repeatedly rate on a scale how likely they think it is that a noise/snake will occur after each image.
Visit 3: Behavioral Tests with Drug or Placebo and MRI scan: For safety reasons, participants will be asked not to take any drugs for at least 24 hours before this visit. They will also be asked not to use marijuana/cannabis for at least 2 weeks before participating. Participants will be required to test negative on a urine drug screen and breathalyzer before continuing with this visit; women must also have a negative pregnancy test. Participants will need to complete a field sobriety test at the end of this visit and will be asked not to drive or operate machinery for the following 24 hours; participants not traveling to the clinic by subway or taxi should arrange to have a friend or family member pick them up.
Two hours before beginning the Visit 3 tasks, participants will be asked to swallow a capsule containing either nabilone or placebo (sugar pill). Nabilone is a Food \& Drug Administration (FDA) approved medication, and the dose (1mg, one time) is unlikely to have any effects that last beyond the duration of the study visit. About every 30 minutes after taking the pill, the participant will fill out some questionnaires asking about how they are feeling at the moment. At the end of the session, they will also be asked to guess whether they received nabilone or placebo.
Participants will then complete a task that is similar to the one on the previous day (Visit 2), but will be completed in the MRI scanner. During the MRI scan, participants will view the same images as on the previous day (Visit 2), and may experience the same aversive stimulus as during Visit 2. They will again be asked to rate how much they expect to experience the aversive stimulus after each image and to self-report their level of anxiety on a scale from 0 to 100. Finally, they will be asked to relax with their eyes open while viewing a white fixation cross on a back background.
Participants will complete an additional task outside of the MRI scanner. Participants will be repeatedly asked to view and choose between different images (e.g., spaceships), which lead to a different set of images. They must select one image from this second set, with some choices leading to a small monetary reward.
Visit 4: Behavioral Tests and MRI scan: This visit will be very similar to Visit 3, except that participants will not receive any study medication. Participants will complete the same type of task inside the MRI scanner, while the study staff measures reaction time, psychophysiological response, and brain activation. Participants will view the same images as in Visits 2 and 3, and may experience the same aversive stimulus. Participants will again be asked to rate how much they expect to experience the aversive stimulus after each image and to report their level of anxiety on a scale from 0 to 100. Participants will again be asked to relax with their eyes open while viewing a white fixation cross on a black background. Finally, outside of the scanner, participants will complete another decision-making task similar to the one they completed the day before.
