Seconded. Keeping in mind that our nerves themselves are operating
based on electricity, I suspect that the basic rule of thumb is:
there's no such thing as safe electrostimulation of sensory nerves.
Your stimulus can either be too weak for anything to be registered at
all, or too strong to be safe.
The margin between these two thresholds on stimulus strength is
probably too small to be safe for everyday usage other than in a
*very* closely controlled environment (say, within shouting distance
of an ICU, with trained medical personnel controlling the apparatus,
given a rather specific medical indication for doing it).
I recall from my bioengineering neuroscience class a
discussion of touch-sensing neurons becoming desensitized
from overstimulation. The classic example was the "glass harmonica"
player of (I think) late 1800s. The device was a series of disks of
different diameters and/or thicknesses that rotated on a shaft.
There may have been some mechanism to keep the rims wetted.
The performer played this by lightly touching the rims with his
fingertips, producing sound like you get from running a wet finger
around the rim of a wineglass. The story is that the real virtuoso
perfomers, who played a lot, eventually lost sensation in their
fingertips. This was apparently only due to overstimulation, since
there was no obvious tissue damage at the surface.
On a personal note, I used a "cheater" method of wood carving
many years ago. I would put a rotary file bit in a high-speed
die grinder (like a Dremel on steroids, or a long skinny router)
and carve away. This made carving a breeze, but after a half
hour or so of carving, I found my fingertips had a very strange
sensation. Even with everything turned off, there was still
a tingling. The strangest part was that if I tapped on something,
it felt like my fingers were little tuning forks... they seemed to
"ring" for a few seconds afterward.
Probably just as well I never made a career of this!
Best regards,
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com