I presume you are performing field recordings with a platinum electrode, which really acts as a capacitor, not as a resistor. Electrical activity of the hippocampal neurons is coupled capacitively through the electrodes to your amplifier system so that Ic= CdV/dt. In other words, current flows only when there is a sudden change in voltage, as in an action potential.

Generally, when doing field recordings there is little need to lower the impedance of wires recording hippocampal field potentials, simply because the HC field activity is so powerful. I usually just use freshly cut 25 or 40 micron tungsten wire. If you're trying to record HC units then you do want a lower impedance for your wires, in that case you want to use much smaller wires (~13-15microns) and gold plate the recording tips to an impedance between 100-200kOhms.

Hi James,

thanks for the information and we currently record from Hippocampal CA1 region and use stainless steel electrodes (monopolar ) and its impedance was 5 Mohm but we tried to reduce the impedance by electrolytic sharpening and i was looking for some alternate way.

thanks a lot for your answer

Hi Binu, Following some of the other answers, to get ride of problems with electrode resistance you have to use a high impedance headstage or field effect transistors. This is common in most electro settings anyway. Wihth high impedance coupling the resistance of the electrode is neglectable. You get near the same extracellular recordings using a metal macro or a sharp micropipette for intracellular recording of 60-100 megohms. Beyond that you have to estimate the lost voltage.

The problems may arise if you attempt to record on DC-coupled mode using metal electrodes, but I assume you don't. Using high impedance headstages also reduces the leak of current from amplifiers to the tissue (through your electrode) reducing other complicating problems.