I'm learning about uncertainty.

I no longer have a reasonable medical explanation for my own experience. An extensive battery of medical tests gives no physical evidence of brain dysfunction. Laboratory results for many of the usual and unusual causes of cognitive impairment have been normal several times over. Two different MRIs of my brain have been negative for brain tumor, stroke or hydrocephalus. Two PET scans give no evidence of Alzheimer's disease or even dementia. And, most disturbing to me, recent neuropsychological testing shows no evidence of any cognitive impairment at all. So intensive medical examination that would be expected to explain my symptoms cannot.

There are no more tests to take. I must learn to live with the uncertainty.

In the past I've not liked uncertainty, but this time it hasn't been so bad. Whatever my impairment is, I've learned a lot over the past year about accepting uncertainty. Despite the uncertainty, I'm actually a lot happier than I was two years ago.

I can only wait and see what develops. Either my symptoms will get better, or they'll stay about the same, or they'll get worse.

If they get better, I don't think I'll really care much about what caused them. If they stay about the same, I'll probably never find out what's causing them, but I'm in good enough shape right now that life would be fine. If my symptoms get worse, the physicians will eventually find evidence of my impairment if not a cause.

So, I just have to wait.

I can partially explain my acceptance because—regardless of why my brain function is slowed—there's no treatment anyway. So the waiting becomes more of a spiritual discipline, a training period for living in the here-and-now and accepting the world as it is.

I'm learning to trust myself .

I'm a child of the Enlightenment, which accepts as definitive truth only things ultimately provable by physical evidence; according to that philosophy, just because I experience something doesn't mean it's real. It could be a mirage, a misunderstanding, a hoax, or all sorts of things that would make my own experience unreliable.

As a physician, I had too many patients whose story simply didn't match the evidence I had. True, for many of them their symptoms were psychosomatic: very real, but due to emotional (not physical) causes.

Some of those contradictions were later resolved by re-examining the lab or x-ray tests. But some were just mysterious.

Unlike most physicians, I suppose, I felt responsible to believe those mysterious stories, trusting my patients' experiences even if I couldn't explain them, yet.

Trusting my own experience in the face of contrary objective evidence, however, is new for me, and it's taking a little bit of practice to get used to it.

I know I'm experiencing cognitive impairment. I trust that it is real, despite the evidence. I'm choosing to trust myself more than the evidence.

This isn't easy for me. Even writing this I feel defensive, vaguely guilty. (Just for you who worry about me, I don't believe I'm guilty of anything; it just feels that way.) But this past year of living with uncertainty about my future has given me some small confidence to trust that I'm okay in the here-and-now.

When I live in the here-and-now, uncertainty about the future ceases to matter.

Editor's note: David's journey with Mild Cognitive Impairment was chronicled in "Fade to Blank: Life Inside Alzheimer's" an in-depth look at the real lives of families impacted by the Alzheimer's epidemic. His story continues on his personal blog on AgingCare.com.