[Eeglablist] inconsistent electrode performance

[Miller, Carol Anne]

Dear EEGLab list,
My question is not about EEGLab, but about my electrode string.  I hope someone out there may have some advice for me!

I have actiCAPslim active electrodes (32 channels) by Brain Products.  We've been using them for several years, without problems, but recently have had difficulty in getting impedances down.  That is, at times the impedances simply won't budge from the highest, even off the charts, level.

I did the saline bath test for the electrodes, they are all functioning, including 2 separate ground electrodes.
The electrodes have been well cared for but definitely needed a thorough cleaning.  We polished them with orange sticks and wiped them with hydrogen peroxide.  Things are better, but performance is still inconsistent.  Recently we've had a) all impedances readily reduced below 10; b) impedances ranging from well below 10 to over 40 after working at it for 20 minutes or so; c) all impedances at max, then suddenly many of them dropped dramatically, but still, after 20 minutes or so, still a wide range of impedance values.  In most cases, the ground electrode will reach low impedance immediately.  It does not seem to be the limiting factor for the other electrodes.

We are prepping participants in the same way we always have--I can't identify a common factor among the "heads" that could explain the inconsistent behavior of the electrodes.

Do we need to clean them again, and if so, how?  Is emery paper an option?  It scares me a little bit.
Is there something else I can trouble-shoot?  I feel like I must be overlooking something.

Thank you,
Carol


Carol A. Miller, Ph.D.

Professor of Communication Sciences and Disorders and Linguistics

404K Ford Building

498 Allen Road

University Park, PA  16802

cam47 at psu.edu

Pronouns:  she/her

My work day may look different than your work day. Please do not feel any pressure to respond out of your normal working hours.