Bridge clamp (was: Re: increase in electrode resistance)

Christian Wilms usenet at
Sun Mar 28 09:57:06 EST 2004

Matt Jones <jonesmat at> wrote:

> Yes, this is what the bridge balance is for. But I don't think it's a
> perfect compensation. I think one can "quite easily compensate the
> voltage drop" as long as that drop is not too high. If it is very
> high, and capacitance compensation is also being used, I believe that
> one runs into problems with oscillations in the bridge circuit that
> can become very large, and destroy the cell. In fact, my thesis
> advisor used to talk about deliberately "ringing" the compensation to
> help with impalements.

Well, my contact with sharps hasn't more than a glance either. In my own
lab work I've only patched so far and there ringing in bridge (current)
clamp doesn't appear to be much of a problem. Was that just luck so far,
or am I on the safe side of things as long as I don't get higher than
say 30 MOhms?

I'm curious on how much of a Rs a bridge will compensate, as combining
this with perforated patch recordings - while probably being quite
tedious - should offer many advantages (recording synaptic potentials
without dialysis of the cell interior ...).

I'm getting the feeling it's time to go look for our lab's edition of
the Axon Guide here ...

Cheers, Chris 

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