[Neuroscience] Re: Brain impedance

Bill via neur-sci%40net.bio.net (by connelly.bill from gmail.com)
Tue Jun 19 23:39:51 EST 2007

Three answers.
1) If you want to stimulate using a known current, buy a constant
current stimulator. This is the only way to be certain. Electrode
resistances change over time due to electroplating, oxidation etc.
However there is nothing wrong with using a constant voltage
stimulator. None of us can know the resistance of your stimulating
electrode, I would not assume it is negligible, especially if it is
fine at the end.

2) Measure it! Next time someone culls an animal in your department,
see if you can use the brain. All you'll need is a $20 dollar
multimeter to get a pretty good idea of the resistance of your
electrode when it is implanted in brain.

3) 50-500uA? Do you actually -need- to be in that range? Surely you
can just work up from 5V up to 20-100V, until you get the result you
are looking for? Indeed, a nice input-output curve (stimulus vs
response) graph is a nice way to indicate your intervention is truly
due to your stimulus and not the implantation/surgery.

On Jun 18, 7:26 am, <Ana.Cervera-Fe... from uv.es> wrote:
> Hi all,
> I want to stimulate through bipolar teflon-coated steel electrodes in
> the tegmentum in rats with pulses of 50-500 uA. I need to know which is
> the average brain impedance in vivo to calculate the voltage needed. I
> suppose that the contribution of the electrode impedance is low but if I
> have to take it into account any advise is welcome.
> Thank you in advance!
> Ana

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