[Neuroscience] Re: Minimizing stimulus artifacts

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Wed Feb 28 22:05:35 EST 2007

On 28 Feb 2007 18:39:08 -0800, "Bill" <connelly.bill from gmail.com> wrote:

>Another dull question: I need tips of minimizing stimulus artifacts. I
>know the best way is to use low stimulus amplitudes/durations and have
>the two poles of your stim. electrode very close together, but that is
>not possible.
>I am told that using a biphasic stimulating paradigm (i.e. the pulse
>changes polarity half way through) is helpful; though I can't find one
>to test that theory out. Has anyone tried that?
>Are there any other tips?
>(I'm running a Grass S88 with it's corresponding stimulus isolator,
>square pulse, constant voltage).

The biphasic vs. monophasic is important only if you have problems
with electrode polarization from running currents always in one
direction through the metal/solution interface.  If you have
reasonable chlorided silver wires, you shouldn't have a problem.

There are lots of different stimulus artifacts and eliminating them is
about as easy (i.e. not at all easy!!!) as eliminating line frequency
noise.  Is the artifact from a separate electrode or is it from
stimulating through the recording electrode?  Those are two very
different situations.  If you have problems with series electrode
resistance, you will definitely have problems passing current through
those electrodes.  "Automatic" compensation methods only work if the
electrode resistance is constant and linear.

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