Frontotemporal dementia -- or FTD -- is the most common and most devastating forms for dementia. As Bill Whitaker tells us, the cause of the illness, which effects many Americans under the age of 60, remains unclear. With Arctic permafrost thawing too quickly, scientists in Siberia are considering drastic measures. Scott Pelley reports. John Green, the best-selling author of books like "The Fault in Our Stars," opens up to Jon Wertheim about exploring his fears through his writing. See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.