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Minimum pulse widths.

Thomas Chimento chimento at neuron.arc.nasa.gov
Thu Feb 22 13:47:35 EST 1996


In article <4faqjc$4ak at castle.nando.net>, "Thomas D. Wason"
<wason at nando.net> wrote:

> Peter Robinson <Peter at oimsdnp.demon.co.uk> wrote:
> >I'm trying to find out what would be the minimum width of an electrical 
> >pulse applied to the skin surface, that would be felt by the person it 
> >was applied to.
> >
> >Alternatively, the minimum energy required before the pulse is felt.
> >
> >Any ideas or pointers to information sources would be appreciated.
> >
> >Peter
> >
> >Peter at oimsdnp.demon.co.uk
> >Peter.Robinson at oxinst.co.uk
> >

Look up human evoded potentials: somatosensory. Some of the references
given before (Buchthal and Rosenfalck) address this question directly. It is
also instructive to simply set up a stimulator with a probe and use youself as
a guinea pig. Apply the pulse to your wrist above the carpal tunnel or at the
elbow (funny bone). Clean the skin with soap and water followed by a good
scrubbing with an alcohol pad. These locations will provoke muscle responses
in the hand. If you want just sensory responses do the same prep on the finger 
tips. 

Below a certain duration, no amout of current will ellicit a response and
above a certain duration you asymptote to a rather low current requirement.
There is a chart that describes these two factors( called rheobase and
chronaxie). 
It plots the relationship between pulse duration and applied current; a
strength/
duration curve. Rheobase is the magnitude of current just sufficient to excite 
a given nerve or muscle. Chronaxie is the length of time a current twice 
rheobase intensity must be applied to produce a response. 

Thomas

-- 
Thomas Chimento                 chimento at neuron.arc.nasa.gov
                        Keep it simple, do it right.



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