Scientists in Liverpool have analysed thousands of paintings from artists who have gone on to develop dementia and Parkinson's. Using a technique called fractal analysis they have detected changes in the painting style up to 20 years before diagnosis [1]. In contrast, painters such as Picasso who, as far as is known, didn't suffer from neurological problems had a constant fractal measure throughout their life.

I suspect that similar results would be found using samples over the years from people's:

- hand writing;

- photographs;

- audio, etc..

Analysis of historical records may be a way of finding out the exact date of onset of the disease. This, in turn, might be linked to potential etiological processes.

Reference:

[1] Art may reveal early signs of dementia - BBC News

John