[Neuroscience] Re: electrode resistance in field potentials

r norman via neur-sci%40net.bio.net (by r_s_norman At _comcast.net)
Sat Jan 27 18:58:26 EST 2007


On Sat, 27 Jan 2007 11:28:57 -0500, "Khaled Moussawi"
<khaledm8 At gmail.com> wrote:

>can anybody explain the effect of electrode resistance on the local field
>potential recorded? and what can be done to improve the sensitivity of this
>technique?
>
In any measurement of potential, the resistance of the electrode has
two effects.  First, if there is any input current drawn by (or
produced by) the amplifier inputs, it will cause IR potentials that
add to the signal.  So make sure you use an amplifier that has in
input impedance at least a couple orders of magnitude larger than your
electrode resistance (to eliminate input currents caused by the
signal, itself) as well as input currents small enough so that the IR
effect is negligible compared with the signal.

Second, random (brownian) movements of electrons in the electrode are,
in fact, currents and will produce electrode noise.  The noise
increases with the  square root of (input resistance times the
bandwidth) of the recording technique.  If you cannot control the
electrode resistance, then the only thing you can do is make sure to
use the smallest bandwidth necessary to record the signal detail.





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