Developing the means to repair the human brain is essential to engineered longevity - it's the one organ we can't just replace as a last resort. From Sentient Developments: "The human brain degrades quickly with advanced age and, as a result, represents the weakest link in the life extension chain; as far as I'm concerned it's full stop until we can meaningfully fix the cognitive problems associated with aging. Yes, age-associated diseases such as cancer and cardiovascular disease are clearly bad, but the most devastating of these involve the nervous system - diseases like Alzheimer's and Parkinson's. These diseases take a brutal toll on individuals and their families, often virtually killing the person well before they die. That we are facing a looming epidemic of neurological diseases shouldn't really come as a surprise to anyone. But what is surprising is that very few people are actively doing anything about it. And it's not that the writing isn't on the wall - it is. The time to act is now. ... Until we can meaningfully treat age-related cognitive decline, many of these other life extending advances are a moot point; what we're in danger of doing right now is extending lifespan, but not necessarily healthy life span." I disagree with this conclusion on the grounds that I think extending life without extending healthy life would be very hard to accomplish even if we were trying - aging is biological damage, and the outcome flows from the state of damage. Reduce the damage and you extend both life and healthy life. Neurodegeneration is driven in large part by the state of general health, perhaps through the mechanisms of blood vessel health, for example.