Credits: Cat Scan, Southern Illinois University/Science Source; EEG, Science Source; MRI, Living Art Enterprises, LLC/Science Source; Person in MRI, Science Source; PET Scan, National Institute on Aging/Science Source; Syringe, Thinkstock; Horizontal cross-section of brain, Laboratory of Neuro Imaging at UCLA and Martinos Center for Biomedical Imaging at MGH, Consortium of the Human Connectome Project