There's no doubt among those 'in the know' that in the foreseeable future we will be able to access new drugs that will permit us to boost our brain functions. Drugs designed to halt or prevent the deterioration of Alzheimer's patients will likely equally be able to enhance the memory of people with brains like mine. My friends and colleagues know all too well that my memory has always been absolutely atrocious, and it is remarkably selective, too. I manage to remember most stuff to do with my work (most, but by no means all important things), yet on the odd occasion I forgot even my own birthday, not to talk about my long-suffering parents' birthdays. In fact, my dear sister has a habit of sending me little reminders that my Mom's or my Dad's birthday are about to come up. Yes, I know, I could, of course, simply set up a reminder in my on-line diary.
But, wouldn't it be nice, if I could simply pop a pill and manage to boost my memory to the point where my sister wouldn't have to remind me, and I wouldn't have to put every little appointment into my diary (incl a detailed description about what it's for etc). Such a drug would clearly enhance my cognitive functions. Now, it's a short step from there, of course, to boosting our regular brain function, too. There is no in principle reason, it seems, why the brain functions of people with lower intelligence could not also be improved over time. Other such drugs might permit people with bad memories (say a traumatic accident) to eliminate such memories altogether.
Now, the question is, of course, whether we should permit people who experience mental states not defined as an illness access to such drugs. Is it acceptable for someone who hasn't Alzheimer's to be given access to a drug that enhances her memory? I can't see why that should not be the case to be honest, because at the end of the day our definition of any given illness fundamentally look toward improving the human condition of someone who is suffering from that condition. Bad memory, traumatic experiences and lower intelligence, to name just a few, all contribute - all other things being equal - to a lower quality of life of those affected by them. There is no good reason to declare them 'not ill' and prevent them from access to such drugs. It is as simple as that, to my mind.