What exactly does "skin conductance" measure??

John H. Casada casad at umich.edu
Mon May 19 15:38:02 EST 1997

Michael Duggan wrote:
> >"John H. Casada" <casad at umich.edu> wrote:
> > This seems to imply that skin conductance is actually measuring salt.
> > This is problematic since the gels used in the electrodes for this
> > contain isotonic saline.  The salt is already present at the electrode
> > site.  Also, skin conductance shows both increases and decreases in a
> > short time.  If it was only salt being measured, this would imply that
> > the skin takes up the salt again.
> >
> So it is not the salt in sweat but the moisture, dry salt is a very
> poor conductor. The water evaporates, explaining the decrease.
> Michael J. Duggan,
It seems that this is not the case.  These changes are occurring in a 
matter of seconds and the gel continues to have water as a base.  
There would be no appreciable evaporation in the time it takes the 
skin conductance to complete a phasic change.  For this reason, it 
seems that the change is not due to either the presence of water or of 
salt.  Another interesting fact concerning skin conductance is that it 
is very sensitive to breathing.  A single deep breath will cause a 
marked increase in skin conductance.

I agree with the previous post that stated that skin conductance 
measured sympathetic activity and arousal state.  This is a robust 
finding.  I do not know, however, what the proximate physiologic 
change is that changes skin conductance.

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