"A graying world will have more of the experience that comes with age. It will also be slower, fuzzier, more forgetful, and just a bit hard of hearing....With the global population of people over 80 expected to more than quadruple to nearly 400 million by 2050, the aging brain will become an increasingly big headache for humankind. Here are four cognitive systems that tend to decline as we age. Get used to these changes. You’ll be seeing a lot more of them in the future."