In June 2021, aducanumab, the first drug to target the cause of Alzheimer's disease, was approved in the US, making headlines worldwide. We look at the results of clinical trials involving over 3,000 participants from 20 countries, differences between the drug and conventional treatments, and the drug's limitations. We also focus on a preceding condition called mild cognitive impairment, or MCI. Japanese researchers developed a way to reverse cognitive decline in those with MCI, and a test to see whether someone is developing it.