I'm not sure where you get that "become a shell" bit from. If anything, I require more and more sensory input as time goes on, but that could just be me being Aspie. I dunno. As for brain aging, consider uploading your mind then perhaps? A hippocampus prosthetic is already being developed, already in FDA animal testing! http://en.wikipedia.org/wiki/Hippocampal_prosthesis http://www.newscientist.com/article/dn3488-worlds-first-brain-prosthesis-revealed.html http://www.newscientist.com/article/dn6574-brain-prosthesis-passes-live-tissue-test.html
But as for how personality changes over time (i'm just guessing that psychological report is strictly psychological, not neurological) that has nothing to do with immortality.
Immortality does not include sensory deprivation, and if you really wanted to stimulate yourself you could go and do something, or if your an upload, simulate stimulation. You could simulate stimulation perfectly, and that would only be necessary for uploads that are just human brains in a computer. Why be that, when you could far exceed the capabilities and limitations of the brain?
Well, you can join me and at least 3 other furs here for the aspergers
1. Psychology is applied neurology, sir, to think that psychology and neurology are unrelated is incorrect
2. I do not consider growing new brains evidence for brains being immortal/only dying because the body dies. Evidence for brain transplants also does not state evidence of the brain being immortal/only dying because the body dies either.
3. Think of it this way, you get a lollypop, it's great the first time, try a lollipop a second time, it's still good, try it a third time, it's not as good, try it a fourth time, still not as good. The stimuli doesn't change, it's just your interpretation of the stimuli.
It can be explained by theory of relativity, to truly get the value of something we need to compare that thing to something else. We compare most things to ourselves for physical differences, oh look that elephant is big, because it's big to us. To a planet, the elephant is small, etc, to really get the true measurement or data of an object, we need to compare it to other things. So how sensory input come into this? Think of it as a graph of standard deviation, to put it in an easy example, if you always are surrounded by good things, you begin to compare. You only have good things to compare to though, so you can only say that these good things are "ok" because to you their true worth isn't very amazing because you are comparing them to everything else in your life, which was good. Good things seem less good, bad things seem more bad.
Have a burger at mcdonalds, doesn't seem so fantastic to you, because you always have burgers at mcdonalds or you have better food, you are comparing the burger to your normal food and it's not fantastic. A homeless person though would think the burger was amazing! Because his comparisons are much less than a burger. To think of it mathematically, it's a global derivative of a graph (y axis happiness, x axis time), it's only a sign on the gradient, which if you are always happy, will be straight. But what if you keep going from happy to sad? The derivitive of that would be all over the place and would never be straight. But then we start to ask, well, sometimes you get used to constant change (ie, the second derivitive may be straight). If you notice someone who has a very static life, is not used to change and will react more severely to someone who's life is always changing. It keeps on going, eventually, you get used to everything, any pattern of your emotional life becomes boring, useless. Nothing becomes interesting.
Remember, if your immortal, you have the chance to do everything feasible.