It isn't so hard to conceive, provided that you don't make the assumption that your thinking process will remain stable after a long time. Most likely it won't.
Brain decay is relevant after you're about 25. Cortical thinning is a very real phenomenon and results in slower responses speeds in elder brains (except for certain types of stimuli, like episodic/experience based recall). There is also some truth in the mathematician's saying that if you didn't make a breakthrough before you're 30, most likely you never will.
Now, there are two counters to this. The first is the "good health" assumption. You can physically be in good health, but unless you stop learning new things and forming new experiences (which involves creating biases to make your judgments and reactions more efficient), your brain is bound to change. For better or worse is hard to say. If you were diagnosed with schizophrenia, for example, expect it to get worse. If you were bipolar, the amplitude of symptoms could worsen as well. (is this in violation of the "good health" assumption? Very likely not -- some of these dysfunctions are very important in creative people). In sum, the things you are currently capable of are a result of a delicate balance of things in your head. Any change in the future does not guarantee anything about your ability to sustain.
The other counter is the "engineering" kind of mentality, where you hedge on the idea that in the future, scientists will discover how to regenerate brain cells. This will probably come true, in some way or another, in this century, and you'd be able to regenerate fresh neurons and repair damaged structures in your brain. You might even be able to gain some unavailable abilities and become native at many many languages. But the flipside is that this flexibility always comes at a price. When you rebuild/repair your brain, the old structures don't remain untouched. This says nothing about your sense of self and its relationship with your current memories and how they shape your ideologies. In other words, if you can rebuild your brain, you could very well become an entirely different person. Now, is this the same person who initially decided to live a very long time?
If you take these ideas into account, living multiple lives is actually not that different from living a single life. Of course, nobody can tell for sure... but you asked.
Brain decay is relevant after you're about 25. Cortical thinning is a very real phenomenon and results in slower responses speeds in elder brains (except for certain types of stimuli, like episodic/experience based recall). There is also some truth in the mathematician's saying that if you didn't make a breakthrough before you're 30, most likely you never will.
Now, there are two counters to this. The first is the "good health" assumption. You can physically be in good health, but unless you stop learning new things and forming new experiences (which involves creating biases to make your judgments and reactions more efficient), your brain is bound to change. For better or worse is hard to say. If you were diagnosed with schizophrenia, for example, expect it to get worse. If you were bipolar, the amplitude of symptoms could worsen as well. (is this in violation of the "good health" assumption? Very likely not -- some of these dysfunctions are very important in creative people). In sum, the things you are currently capable of are a result of a delicate balance of things in your head. Any change in the future does not guarantee anything about your ability to sustain.
The other counter is the "engineering" kind of mentality, where you hedge on the idea that in the future, scientists will discover how to regenerate brain cells. This will probably come true, in some way or another, in this century, and you'd be able to regenerate fresh neurons and repair damaged structures in your brain. You might even be able to gain some unavailable abilities and become native at many many languages. But the flipside is that this flexibility always comes at a price. When you rebuild/repair your brain, the old structures don't remain untouched. This says nothing about your sense of self and its relationship with your current memories and how they shape your ideologies. In other words, if you can rebuild your brain, you could very well become an entirely different person. Now, is this the same person who initially decided to live a very long time?
If you take these ideas into account, living multiple lives is actually not that different from living a single life. Of course, nobody can tell for sure... but you asked.