Dr. Allan Ropper speaks with residents and fellows as they do rounds at the neuroscience intensive care unit at Brigham and Women's Hospital in Boston. M. Scott Brauer for NPR hide caption

itoggle caption M. Scott Brauer for NPR

Kent Stephenson, a research participant at the University of Louisville's Kentucky Spinal Cord Injury Research Center, has his level of muscle activity and force measured by Katelyn Gurley. Courtesy of the University of Louisville hide caption

itoggle caption Courtesy of the University of Louisville

Deep brain stimulation eased Shari Finsilver's tremors, but didn't stop them entirely. Here she uses both hands to stabilize a glass of water. Marvin Shaouni for NPR hide caption

itoggle caption Marvin Shaouni for NPR

Could the images common in accounts of near-death experiences be explained by a rush of electrical activity in the brain? Odina/iStockphoto.com hide caption

itoggle caption Odina/iStockphoto.com

Dr. Jame Abraham used positron emission tomography, or PET, scans to understand differences in brain metabolism before and after chemotherapy. Dr. Jame Abraham hide caption

itoggle caption Dr. Jame Abraham

Pinwheels like these are often used to test nerve responses. iStockphoto.com hide caption

itoggle caption iStockphoto.com