Imagine an optometrist giving you an eye exam. You're sitting in a chair looking through trial frames. The optometrist picks a lens, slots it into the frame and asks you to look at an eye chart. You decide whether your vision is better or worse with the new lens and the process repeats, potentially starting from a new baseline.
Now imagine a version of this exam that involves a "neurometrist", a neuroscientist adjusting your state of mind with a combination of drugs, transcranial stimulation and/or brain implants and then alternately showing you what the world feels like with and without the adjustment. If you consider your altered state of mind an improvement your neurometrist locks it permanently in place the process is repeated.
People make bad choices with the mind-altering technology available today, so we should generally be wary of incremental hill-climbing when it comes to our psychological state. For some people ([though surprisingly not everyone](http://smartdrugsmarts.com/episode-154-addiction-maia-szalavitz/)), taking heroin temporarily feels like an improvement. You could picture an evil neurometrist injecting people with heroin slowly leading them into a life of misery and addiction.
So, for the thought experience, assume that our neurometrist is not evil and in addition smart enough to avoid letting you slide into a local optimum. You can trust that the gains you make in the procedure will be permanent, and that that there are no states you'd be likely to find that are substantially more pleasurable or subjectively meaningful than the one you find yourself in after the procedure.
But while our neurometrist is not evil, he is also thoroughly agnostic about what constitutes a meaningful life. If you would truly prefer to be a brain in a vat having its pleasure centers stimulated rather than living a life of meaningful toil, than that's where you'll end up.
So the question is: How should you choose whether to accept a change that the neurometrist presents to you? Should you simply go with what feels better in each step, or reflect whether a given change aligns with your values and notions of a meaningful existence?
I would argue that you should go with what feels better and that you should not be concerned with whether the change aligns with your values. Your values may simply be parochial byproducts of human evolution. Our eternal values may simply be particular strategies for survival and reproduction. In this case, why should the loss of your values be any more meaningful than the loss of, say, the physical body, or the leaving behind of traditional social structures?
If on the other hand, some values are intrinsically meaningful in the sense that sustained meaning can only be derived by instantiating those values in your life, then the process the neurometrist would put you through should steer you towards those values.