Participation in this study will last approximately 3 months. Four groups of participants will be recruited: healthy controls and people with PD, GAD, or social phobia (SP). All participants will undergo functional magnetic resonance imaging (fMRI) scanning—a measure of brain functioning—at the first visit. During the fMRI scan, participants will be asked to perform computerized tasks that involve responding to images. This will be the only visit that the healthy controls and people with SP complete; their inclusion in the study establishes a comparison point for the brain scans of the other participants. People with PD and GAD will then be asked to complete 10 sessions of CBT over a 10- to 14-week period. After 3 months, these participants will again undergo fMRI scanning. At 3 and 6 months after the completion of CBT, these participants will be asked to complete follow-up questionnaires about their anxiety.