The one concept of Parkinsonian writing/Parkinsonian movement is that the tremor is only one part (and is often variable - as it is a rest tremor that actually disappears with intention or movement). There are some folks that do have shaky letters but others will not.<p>The other interesting part of it is that the spatial representation of the letters/hand/arm movements, and indeed of limb movements in space, is that it shrinks over time. The term is micrographia. I think the whole idea of how 3D space is represented in the brain is still far from clear, but whoever is able to come up with a good reproducible model would be really onto something<p>(*I would also bet that maybe it's different/distinct from the hippocampal "place" or "grid" cells that won the Mosers the Nobel)..