Likes sitting in boxes
In whatever form immortality, or extended lifespan, may take, the development of artificially enhanced memory storage and retreival regimes may be helpful. Every other body system might work ok if we could just keep it patching it; for example, knees, nerves and digestion may work more-or-less the same if we can replace wornout parts. Even the parts of the brain that are not mostly about long-term memory may work fine if replaced, when worn out, with duplicates (...passing over the great difficulty of doing so....)
But memory is inherently cumulative, and eventually may bump up against some limit inherent to the lack-of-design of the original. That's not necessarily a terrible problem. So long as one retains enough memory to be able to access "extended memory", future immortals may be happy with their condition even though the result may be mental processes radically different from those we enjoy today. I'm sure plenty of SF authors have exploited this concept (I'm thinking of a short story decades ago about a future cop entitled something like "Jorge Changes His Mind") but it amuses me to see my photo collection taking the first primitive steps down that road.