6. Subjects who are currently taking oral medications known to affect muscarinic acetylcholine receptor binding in the central nervous system. Of note, some over-the counter-medications are known to affect muscarinic acetylcholine receptor binding. Subjects who use medications known to affect muscarinic acetylcholine receptor binding, such as first generation antihistamines for common cold and allergy symptoms and sleep aids for insomnia, occasionally on an as needed basis may be enrolled in this study. Furthermore, these as needed medications should be paused for at least 3 days before PET scanning. This three-day period is equivalent to about 4 to 5 half lives for these medications. In addition, subjects who use topical antimuscarinic medications, such as eye drops for glaucoma and inhalers, may be enrolled in this study because topical antimuscarinic medications have negligible systemic bioavailability. Subjects who have contraindications to MRI, ferromagnetic objects in their bodies (e.g., implanted stimulators including deep brain stimulation, aneurysm clips, prosthesis, artificial heart valves, etc.) that cannot be removed for the purpose of study participation.