BioSemi.nl

Hello,

I have been running ABR experiments in my lab, and today I noticed that the external electrodes that we use for the ABR tiptrodes are giving us a large, unexpected waveform. Neither the other externals, nor any of the bundle electrodes seemed to be giving us any trouble. I do not know if this is relevant, but the tiptrodes also had very high DC Offsets (~150mV) for this subject. Any advice or pointers would be greatly appreciated. Please let me know if there is any more information I can provide.

Thank you,
Andrew

There is high 50/60 Hz mains interference on the tiptrode channels. How did you connect the tiptrode to the EX input ? If you used a long (more than a few cm) unshielded wire, then that explains the high interference level.

Higher offsets for the tiptrodes are normal (gold vs AgAgCl electrode material).

Best regards, Coen (BioSemi)

Hi Coen,

Thank you! Yes, we are using a long, unshielded wire (~5ft). What struck me as odd is that we have not experienced such high interference during previous ABRs sessions. In addition, is it strange that the other nearby external electrodes (EXG 1 & 2), with unshielded cables of similar length, are not experiencing any of that same interference?

Kind regards,
Andrew

I assume that EX1 and EX2 are active electrodes, and therefore they do not generate interference with unshielded cables. The (unshielded) length of cable between the tiptrode and active electrode circuit should not be more than a few inches.

Best regards, Coen (BioSemi)

Hi Coen,

Yes, EX1 and EX2 are active electrodes. Thank you for the advice, I will shield the cables moving forward.

I'm not sure if I should start a separate thread for this, but when using these same ABR inline cables, I got a different kind of interference (attached: this time the cables are plugged into EXG1 and EXG2). I am not sure what is causing the problem, but it appears most often when the cables are being moved. Could this be a short?

Thank you,
Andrew

Do not shield the cables (a suitable drive signal for the shields is not readily available), reduce the length to a few inches.

The spikes look like a contact problem (a short circuit would make the blue light blink).

Best regards, Coen (Biosemi)