[Neuroscience] Re: stimulation electrodes

jonesmat via neur-sci%40net.bio.net (by mathewjones from wisc.edu)
Fri Aug 5 13:58:14 EST 2011


On Jul 17, 10:57 am, daniela spitz <danielaspi... from googlemail.com>
wrote:
> Hi,
>
> I would like to know the difference between monopolar and bipolar
> stimulating electrodes. I can imagine that the strength and actual area
> being stimulated (in slices) could be changed with different sizes of
> bipolar electrodes. But, to select between mono and bipolar electrodes is
> bit puzzling for me. Anywhere I could get literature on this?
>
> thanks
> daniela
>
> ps: sorry, if this question could be a basic thing for you, but for me, not.


Hi,

In reality, all electrodes have to be bipolar in some sense, because
there always has to be a (+) and a (-) pole in order to pass any
current. But when people say monopolar, they usually mean that one
pole is the "electrode" which you stick into the tissue, and the other
pole is a "ground" wire sitting far away in the bath (usually *not*
the same as the ground for your recording amplifier). In contrast,
bipolar usually means a pair of wires that are close together, like a
fork, that you stick into the tissue next to each other. The idea is
that this "should" help to restrict the electric field and make it
more local so that you're not stimulating things you don't want to.
Also, there are at least two common kinds of bipolar: 1) a pair of
parallel wires, or 2) an inner wire as one pole, wrapped in an
insulating material, which is then coated with a second conductive
shell. These are called "concentric" electrodes.

Which type you use depends on your specific needs. In general, if you
want the most local stimulus, probably a bipolar electrode is better.
One can also make very small, very local stimulating electrodes by
using "theta" glass (i.e., double-barreled glass pipetes) that you
pull down to ~1um with a pipette puller. Then fill them with ACSF, and
run a wire down each barrel to connect to the stimulator.

Cheers,

Matt






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